1.4.0b1

Released: November 2, 2020

general

[general] [change] "python setup.py test" is no longer a test runner, as this is deprecated by
Pypa. Please use "tox" with no arguments for a basic test run.
References: #4789
[general] [bug] Refactored the internal conventions used to cross-import modules that have
mutual dependencies between them, such that the inspected arguments of
functions and methods are no longer modified. This allows tools like
pylint, Pycharm, other code linters, as well as hypothetical pep-484
implementations added in the future to function correctly as they no longer
see missing arguments to function calls. The new approach is also
simpler and more performant.
References: #4656, #4689

platform

[platform] [change] The importlib_metadata library is used to scan for setuptools
entrypoints rather than pkg_resources. as importlib_metadata is a small
library that is included as of Python 3.8, the compatibility library is
installed as a dependency for Python versions older than 3.8.
References: #5400
[platform] [change] Installation has been modernized to use setup.cfg for most package
metadata.
References: #5404
[platform] [removed] Dropped support for python 3.4 and 3.5 that has reached EOL. SQLAlchemy 1.4
series requires python 2.7 or 3.6+.
References: #5634
[platform] [removed] Removed all dialect code related to support for Jython and zxJDBC. Jython
has not been supported by SQLAlchemy for many years and it is not expected
that the current zxJDBC code is at all functional; for the moment it just
takes up space and adds confusion by showing up in documentation. At the
moment, it appears that Jython has achieved Python 2.7 support in its
releases but not Python 3. If Jython were to be supported again, the form
it should take is against the Python 3 version of Jython, and the various
zxJDBC stubs for various backends should be implemented as a third party
dialect.
References: #5094

orm

[orm] [feature] The ORM can now generate queries previously only available when using
_orm.Query using the _sql.select() construct directly.
A new system by which ORM "plugins" may establish themselves within a
Core _sql.Select allow the majority of query building logic
previously inside of _orm.Query to now take place within
a compilation-level extension for _sql.Select. Similar changes
have been made for the _sql.Update and _sql.Delete
constructs as well. The constructs when invoked using _orm.Session.execute()
now do ORM-related work within the method. For _sql.Select,
the _engine.Result object returned now contains ORM-level
entities and results.
References: #5159
[orm] [feature] Added the ability to add arbitrary criteria to the ON clause generated
by a relationship attribute in a query, which applies to methods such
as _query.Query.join() as well as loader options like
_orm.joinedload(). Additionally, a "global" version of the option
allows limiting criteria to be applied to particular entities in
a query globally.
References: #4472
[orm] [feature] The ORM Declarative system is now unified into the ORM itself, with new
import spaces under sqlalchemy.orm and new kinds of mappings. Support
for decorator-based mappings without using a base class, support for
classical style-mapper() calls that have access to the declarative class
registry for relationships, and full integration of Declarative with 3rd
party class attribute systems like dataclasses and attrs is now
supported.
References: #5508
[orm] [feature] Eager loaders, such as joined loading, SELECT IN loading, etc., when
configured on a mapper or via query options will now be invoked during
the refresh on an expired object; in the case of selectinload and
subqueryload, since the additional load is for a single object only,
the "immediateload" scheme is used in these cases which resembles the
single-parent query emitted by lazy loading.
References: #1763
[orm] [feature] Added support for direct mapping of Python classes that are defined using
the Python dataclasses decorator. Pull request courtesy Václav
Klusák. The new feature integrates into new support at the Declarative
level for systems such as dataclasses and attrs.
References: #5027
[orm] [feature] Added "raiseload" feature for ORM mapped columns via orm.defer.raiseload
parameter on defer() and deferred(). This provides
similar behavior for column-expression mapped attributes as the
raiseload() option does for relationship mapped attributes. The
change also includes some behavioral changes to deferred columns regarding
expiration; see the migration notes for details.
References: #4826
[orm] [usecase] The evaluator that takes place within the ORM bulk update and delete for
synchronize_session="evaluate" now supports the IN and NOT IN operators.
Tuple IN is also supported.
References: #1653
[orm] [usecase] Enhanced logic that tracks if relationships will be conflicting with each
other when they write to the same column to include simple cases of two
relationships that should have a "backref" between them. This means that
if two relationships are not viewonly, are not linked with back_populates
and are not otherwise in an inheriting sibling/overriding arrangement, and
will populate the same foreign key column, a warning is emitted at mapper
configuration time warning that a conflict may arise. A new parameter
_orm.relationship.overlaps is added to suit those very rare cases
where such an overlapping persistence arrangement may be unavoidable.
References: #5171
[orm] [usecase] The ORM bulk update and delete operations, historically available via the
_orm.Query.update() and _orm.Query.delete() methods as well as
via the _dml.Update and _dml.Delete constructs for
:term:2.0 style execution, will now automatically accommodate for the
additional WHERE criteria needed for a single-table inheritance
discriminator in order to limit the statement to rows referring to the
specific subtype requested. The new _orm.with_loader_criteria()
construct is also supported for with bulk update/delete operations.
Unknown interpreted text role "term".
References: #3903, #5018
[orm] [usecase] Update _orm.relationship.sync_backref flag in a relationship
to make it implicitly False in viewonly=True relationships,
preventing synchronization events.
References: #5237
[orm] [change] The condition where a pending object being flushed with an identity that
already exists in the identity map has been adjusted to emit a warning,
rather than throw a FlushError. The rationale is so that the
flush will proceed and raise a IntegrityError instead, in the
same way as if the existing object were not present in the identity map
already. This helps with schemes that are using the
IntegrityError as a means of catching whether or not a row
already exists in the table.
References: #4662
[orm] [change] [sql] A selection of Core and ORM query objects now perform much more of their
Python computational tasks within the compile step, rather than at
construction time. This is to support an upcoming caching model that will
provide for caching of the compiled statement structure based on a cache
key that is derived from the statement construct, which itself is expected
to be newly constructed in Python code each time it is used. This means
that the internal state of these objects may not be the same as it used to
be, as well as that some but not all error raise scenarios for various
kinds of argument validation will occur within the compilation / execution
phase, rather than at statement construction time. See the migration
notes linked below for complete details.
[orm] [change] The automatic uniquing of rows on the client side is turned off for the new
:term:2.0 style of ORM querying. This improves both clarity and
performance. However, uniquing of rows on the client side is generally
necessary when using joined eager loading for collections, as there
will be duplicates of the primary entity for each element in the
collection because a join was used. This uniquing must now be manually
enabled and can be achieved using the new
_engine.Result.unique() modifier. To avoid silent failure, the ORM
explicitly requires the method be called when the result of an ORM
query in 2.0 style makes use of joined load collections. The newer
_orm.selectinload() strategy is likely preferable for eager loading
of collections in any case.
Unknown interpreted text role "term".
References: #4395
[orm] [change] The ORM will now warn when asked to coerce a _expression.select() construct into
a subquery implicitly. This occurs within places such as the
_query.Query.select_entity_from() and _query.Query.select_from() methods
as well as within the with_polymorphic() function. When a
_expression.SelectBase (which is what's produced by _expression.select()) or
_query.Query object is passed directly to these functions and others,
the ORM is typically coercing them to be a subquery by calling the
_expression.SelectBase.alias() method automatically (which is now superseded by
the _expression.SelectBase.subquery() method). See the migration notes linked
below for further details.
References: #4617
[orm] [change] The "KeyedTuple" class returned by _query.Query is now replaced with the
Core Row class, which behaves in the same way as KeyedTuple.
In SQLAlchemy 2.0, both Core and ORM will return result rows using the same
Row object. In the interim, Core uses a backwards-compatibility
class LegacyRow that maintains the former mapping/tuple hybrid
behavior used by "RowProxy".
References: #4710
[orm] [performance] The bulk update and delete methods Query.update() and
Query.delete(), as well as their 2.0-style counterparts, now make
use of RETURNING when the "fetch" strategy is used in order to fetch the
list of affected primary key identites, rather than emitting a separate
SELECT, when the backend in use supports RETURNING. Additionally, the
"fetch" strategy will in ordinary cases not expire the attributes that have
been updated, and will instead apply the updated values directly in the
same way that the "evaluate" strategy does, to avoid having to refresh the
object. The "evaluate" strategy will also fall back to expiring
attributes that were updated to a SQL expression that was unevaluable in
Python.
[orm] [performance] [postgresql] Implemented support for the psycopg2 execute_values() extension
within the ORM flush process via the enhancements to Core made
in #5401, so that this extension is used
both as a strategy to batch INSERT statements together as well as
that RETURNING may now be used among multiple parameter sets to
retrieve primary key values back in batch. This allows nearly
all INSERT statements emitted by the ORM on behalf of PostgreSQL
to be submitted in batch and also via the execute_values()
extension which benches at five times faster than plain
executemany() for this particular backend.
References: #5263
[orm] [bug] A query that is against a mapped inheritance subclass which also uses
_query.Query.select_entity_from() or a similar technique in order to
provide an existing subquery to SELECT from, will now raise an error if the
given subquery returns entities that do not correspond to the given
subclass, that is, they are sibling or superclasses in the same hierarchy.
Previously, these would be returned without error. Additionally, if the
inheritance mapping is a single-inheritance mapping, the given subquery
must apply the appropriate filtering against the polymorphic discriminator
column in order to avoid this error; previously, the _query.Query would
add this criteria to the outside query however this interferes with some
kinds of query that return other kinds of entities as well.
References: #5122
[orm] [bug] The internal attribute symbols NO_VALUE and NEVER_SET have been unified, as
there was no meaningful difference between these two symbols, other than a
few codepaths where they were differentiated in subtle and undocumented
ways, these have been fixed.
References: #4696
[orm] [bug] Fixed bug where a versioning column specified on a mapper against a
_expression.select() construct where the version_id_col itself were against the
underlying table would incur additional loads when accessed, even if the
value were locally persisted by the flush. The actual fix is a result of
the changes in #4617, by fact that a _expression.select() object no
longer has a .c attribute and therefore does not confuse the mapper
into thinking there's an unknown column value present.
References: #4194
[orm] [bug] An UnmappedInstanceError is now raised for InstrumentedAttribute
if an instance is an unmapped object. Prior to this an AttributeError
was raised. Pull request courtesy Ramon Williams.
References: #3858
[orm] [bug] The Session object no longer initiates a
SessionTransaction object immediately upon construction or after
the previous transaction is closed; instead, "autobegin" logic now
initiates the new SessionTransaction on demand when it is next
needed. Rationale includes to remove reference cycles from a
Session that has been closed out, as well as to remove the
overhead incurred by the creation of SessionTransaction objects
that are often discarded immediately. This change affects the behavior of
the SessionEvents.after_transaction_create() hook in that the event
will be emitted when the Session first requires a
SessionTransaction be present, rather than whenever the
Session were created or the previous SessionTransaction
were closed. Interactions with the _engine.Engine and the database
itself remain unaffected.
References: #5074
[orm] [bug] Added new entity-targeting capabilities to the ORM query context
help with the case where the Session is using a bind dictionary
against mapped classes, rather than a single bind, and the _query.Query
is against a Core statement that was ultimately generated from a method
such as _query.Query.subquery(). First implemented using a deep
search, the current approach leverages the unified _sql.select()
construct to keep track of the first mapper that is part of
the construct.
References: #4829
[orm] [bug] [inheritance] An ArgumentError is now raised if both the selectable and
flat parameters are set to True in orm.with_polymorphic(). The
selectable name is already aliased and applying flat=True overrides the
selectable name with an anonymous name that would've previously caused the
code to break. Pull request courtesy Ramon Williams.
References: #4212
[orm] [bug] Fixed issue in polymorphic loading internals which would fall back to a
more expensive, soon-to-be-deprecated form of result column lookup within
certain unexpiration scenarios in conjunction with the use of
"with_polymorphic".
References: #4718
[orm] [bug] An error is raised if any persistence-related "cascade" settings are made
on a _orm.relationship() that also sets up viewonly=True. The "cascade"
settings now default to non-persistence related settings only when viewonly
is also set. This is the continuation from #4993 where this
setting was changed to emit a warning in 1.3.
References: #4994
[orm] [bug] Improved declarative inheritance scanning to not get tripped up when the
same base class appears multiple times in the base inheritance list.
References: #4699
[orm] [bug] Fixed bug in ORM versioning feature where assignment of an explicit
version_id for a counter configured against a mapped selectable where
version_id_col is against the underlying table would fail if the previous
value were expired; this was due to the fact that the mapped attribute
would not be configured with active_history=True.
References: #4195
[orm] [bug] An exception is now raised if the ORM loads a row for a polymorphic
instance that has a primary key but the discriminator column is NULL, as
discriminator columns should not be null.
References: #4836
[orm] [bug] Accessing a collection-oriented attribute on a newly created object no
longer mutates __dict__, but still returns an empty collection as has
always been the case. This allows collection-oriented attributes to work
consistently in comparison to scalar attributes which return None, but
also don't mutate __dict__. In order to accommodate for the collection
being mutated, the same empty collection is returned each time once
initially created, and when it is mutated (e.g. an item appended, added,
etc.) it is then moved into __dict__. This removes the last of
mutating side-effects on read-only attribute access within the ORM.
References: #4519
[orm] [bug] The refresh of an expired object will now trigger an autoflush if the list
of expired attributes include one or more attributes that were explicitly
expired or refreshed using the Session.expire() or
Session.refresh() methods. This is an attempt to find a middle
ground between the normal unexpiry of attributes that can happen in many
cases where autoflush is not desirable, vs. the case where attributes are
being explicitly expired or refreshed and it is possible that these
attributes depend upon other pending state within the session that needs to
be flushed. The two methods now also gain a new flag
Session.expire.autoflush and
Session.refresh.autoflush, defaulting to True; when set to
False, this will disable the autoflush that occurs on unexpire for these
attributes.
References: #5226
[orm] [bug] The behavior of the _orm.relationship.cascade_backrefs flag
will be reversed in 2.0 and set to False unconditionally, such that
backrefs don't cascade save-update operations from a forwards-assignment to
a backwards assignment. A 2.0 deprecation warning is emitted when the
parameter is left at its default of True at the point at which such a
cascade operation actually takes place. The new behavior can be
established as always by setting the flag to False on a specific
_orm.relationship(), or more generally can be set up across the board
by setting the the _orm.Session.future flag to True.
References: #5150
[orm] [deprecated] The "slice index" feature used by _orm.Query as well as by the
dynamic relationship loader will no longer accept negative indexes in
SQLAlchemy 2.0. These operations do not work efficiently and load the
entire collection in, which is both surprising and undesirable. These
will warn in 1.4 unless the _orm.Session.future flag is set in
which case they will raise IndexError.
References: #5606
[orm] [deprecated] Calling the _query.Query.instances() method without passing a
QueryContext is deprecated. The original use case for this was
that a _query.Query could yield ORM objects when given only the entities
to be selected as well as a DBAPI cursor object. However, for this to work
correctly there is essential metadata that is passed from a SQLAlchemy
_engine.ResultProxy that is derived from the mapped column expressions,
which comes originally from the QueryContext. To retrieve ORM
results from arbitrary SELECT statements, the _query.Query.from_statement()
method should be used.
References: #4719
[orm] [deprecated] Using strings to represent relationship names in ORM operations such as
_orm.Query.join(), as well as strings for all ORM attribute names
in loader options like _orm.selectinload()
is deprecated and will be removed in SQLAlchemy 2.0. The class-bound
attribute should be passed instead. This provides much better specificity
to the given method, allows for modifiers such as of_type(), and
reduces internal complexity.
Additionally, the aliased and from_joinpoint parameters to
_orm.Query.join() are also deprecated. The _orm.aliased()
construct now provides for a great deal of flexibility and capability
and should be used directly.
References: #4705, #5202
[orm] [deprecated] Deprecated logic in _query.Query.distinct() that automatically adds
columns in the ORDER BY clause to the columns clause; this will be removed
in 2.0.
References: #5134
[orm] [deprecated] Passing keyword arguments to methods such as _orm.Session.execute()
to be passed into the _orm.Session.get_bind() method is deprecated;
the new _orm.Session.execute.bind_arguments dictionary should
be passed instead.
References: #5573
[orm] [deprecated] The eagerload() and relation() were old aliases and are
now deprecated. Use _orm.joinedload() and _orm.relationship()
respectively.
References: #5192
[orm] [removed] All long-deprecated "extension" classes have been removed, including
MapperExtension, SessionExtension, PoolListener, ConnectionProxy,
AttributeExtension. These classes have been deprecated since version 0.7
long superseded by the event listener system.
References: #4638
[orm] [removed] Remove the deprecated loader options joinedload_all, subqueryload_all,
lazyload_all, selectinload_all. The normal version with method chaining
should be used in their place.
References: #4642
[orm] [removed] Remove deprecated function comparable_property. Please refer to the
~sqlalchemy.ext.hybrid extension. This also removes the function
comparable_using in the declarative extension.
Remove deprecated function compile_mappers. Please use
configure_mappers()
Remove deprecated method collection.linker. Please refer to the
AttributeEvents.init_collection() and
AttributeEvents.dispose_collection() event handlers.
Remove deprecated method Session.prune and parameter
Session.weak_identity_map. See the recipe at
session_referencing_behavior for an event-based approach to
maintaining strong identity references.
This change also removes the class StrongInstanceDict.
Remove deprecated parameter mapper.order_by. Use _query.Query.order_by()
to determine the ordering of a result set.
Remove deprecated parameter Session._enable_transaction_accounting.
Remove deprecated parameter Session.is_modified.passive.
References: #4643

engine

[engine] [feature] Implemented an all-new _result.Result object that replaces the previous
ResultProxy object. As implemented in Core, the subclass
_result.CursorResult features a compatible calling interface with the
previous ResultProxy, and additionally adds a great amount of new
functionality that can be applied to Core result sets as well as ORM result
sets, which are now integrated into the same model. _result.Result
includes features such as column selection and rearrangement, improved
fetchmany patterns, uniquing, as well as a variety of implementations that
can be used to create database results from in-memory structures as well.
References: #4395, #4959, #5087
[engine] [feature] [orm] SQLAlchemy now includes support for Python asyncio within both Core and
ORM, using the included asyncio extension <asyncio_toplevel>. The
extension makes use of the greenlet library in order to adapt
SQLAlchemy's sync-oriented internals such that an asyncio interface that
ultimately interacts with an asyncio database adapter is now feasible. The
single driver supported at the moment is the
dialect-postgresql-asyncpg driver for PostgreSQL.
References: #3414
[engine] [feature] [alchemy2] Implemented the _sa.create_engine.future parameter which
enables forwards compatibility with SQLAlchemy 2. is used for forwards
compatibility with SQLAlchemy 2. This engine features
always-transactional behavior with autobegin.
References: #4644
[engine] [feature] [pyodbc] Reworked the "setinputsizes()" set of dialect hooks to be correctly
extensible for any arbirary DBAPI, by allowing dialects individual hooks
that may invoke cursor.setinputsizes() in the appropriate style for that
DBAPI. In particular this is intended to support pyodbc's style of usage
which is fundamentally different from that of cx_Oracle. Added support
for pyodbc.
References: #5649
[engine] [feature] Added new reflection method Inspector.get_sequence_names() which
returns all the sequences defined and Inspector.has_sequence() to
check if a particular sequence exits.
Support for this method has been added to the backend that support
Sequence: PostgreSQL, Oracle and MariaDB >= 10.3.
References: #2056
[engine] [feature] The _schema.Table.autoload_with parameter now accepts an _reflection.Inspector object
directly, as well as any _engine.Engine or _engine.Connection as was the case before.
References: #4755
[engine] [change] The RowProxy class is no longer a "proxy" object, and is instead
directly populated with the post-processed contents of the DBAPI row tuple
upon construction. Now named Row, the mechanics of how the
Python-level value processors have been simplified, particularly as it impacts the
format of the C code, so that a DBAPI row is processed into a result tuple
up front. The object returned by the _engine.ResultProxy is now the
LegacyRow subclass, which maintains mapping/tuple hybrid behavior,
however the base Row class now behaves more fully like a named
tuple.
References: #4710
[engine] [performance] The pool "pre-ping" feature has been refined to not invoke for a DBAPI
connection that was just opened in the same checkout operation. pre ping
only applies to a DBAPI connection that's been checked into the pool
and is being checked out again.
References: #4524
[engine] [performance] [change] [py3k] Disabled the "unicode returns" check that runs on dialect startup when
running under Python 3, which for many years has occurred in order to test
the current DBAPI's behavior for whether or not it returns Python Unicode
or Py2K strings for the VARCHAR and NVARCHAR datatypes. The check still
occurs by default under Python 2, however the mechanism to test the
behavior will be removed in SQLAlchemy 2.0 when Python 2 support is also
removed.
This logic was very effective when it was needed, however now that Python 3
is standard, all DBAPIs are expected to return Python 3 strings for
character datatypes. In the unlikely case that a third party DBAPI does
not support this, the conversion logic within String is still
available and the third party dialect may specify this in its upfront
dialect flags by setting the dialect level flag returns_unicode_strings
to one of String.RETURNS_CONDITIONAL or
String.RETURNS_BYTES, both of which will enable Unicode conversion
even under Python 3.
References: #5315
[engine] [bug] Revised the Connection.execution_options.schema_translate_map
feature such that the processing of the SQL statement to receive a specific
schema name occurs within the execution phase of the statement, rather than
at the compile phase. This is to support the statement being efficiently
cached. Previously, the current schema being rendered into the statement
for a particular run would be considered as part of the cache key itself,
meaning that for a run against hundreds of schemas, there would be hundreds
of cache keys, rendering the cache much less performant. The new behavior
is that the rendering is done in a similar manner as the "post compile"
rendering added in 1.4 as part of #4645, #4808.
References: #5004
[engine] [bug] The _engine.Connection object will now not clear a rolled-back
transaction until the outermost transaction is explicitly rolled back.
This is essentially the same behavior that the ORM Session has
had for a long time, where an explicit call to .rollback() on all
enclosing transactions is required for the transaction to logically clear,
even though the DBAPI-level transaction has already been rolled back.
The new behavior helps with situations such as the "ORM rollback test suite"
pattern where the test suite rolls the transaction back within the ORM
scope, but the test harness which seeks to control the scope of the
transaction externally does not expect a new transaction to start
implicitly.
References: #4712
[engine] [bug] Adjusted the dialect initialization process such that the
_engine.Dialect.on_connect() is not called a second time
on the first connection. The hook is called first, then the
_engine.Dialect.initialize() is called if that connection is the
first for that dialect, then no more events are called. This eliminates
the two calls to the "on_connect" function which can produce very
difficult debugging situations.
References: #5497
[engine] [deprecated] The _engine.URL object is now an immutable named tuple. To modify
a URL object, use the _engine.URL.set() method to produce a new URL
object.
References: #5526
[engine] [deprecated] The _schema.MetaData.bind argument as well as the overall
concept of "bound metadata" is deprecated in SQLAlchemy 1.4 and will be
removed in SQLAlchemy 2.0. The parameter as well as related functions now
emit a _exc.RemovedIn20Warning when deprecation_20_mode is
in use.
References: #4634
[engine] [deprecated] The server_side_cursors engine-wide parameter is deprecated and will be
removed in a future release. For unbuffered cursors, the
_engine.Connection.execution_options.stream_results execution
option should be used on a per-execution basis.
[engine] [deprecated] The _engine.Connection.connect() method is deprecated as is the concept of
"connection branching", which copies a _engine.Connection into a new one
that has a no-op ".close()" method. This pattern is oriented around the
"connectionless execution" concept which is also being removed in 2.0.
References: #5131
[engine] [deprecated] The case_sensitive flag on _sa.create_engine() is
deprecated; this flag was part of the transition of the result row object
to allow case sensitive column matching as the default, while providing
backwards compatibility for the former matching method. All string access
for a row should be assumed to be case sensitive just like any other Python
mapping.
References: #4878
[engine] [deprecated] "Implicit autocommit", which is the COMMIT that occurs when a DML or DDL
statement is emitted on a connection, is deprecated and won't be part of
SQLAlchemy 2.0. A 2.0-style warning is emitted when autocommit takes
effect, so that the calling code may be adjusted to use an explicit
transaction.
As part of this change, DDL methods such as
_schema.MetaData.create_all() when used against an
_engine.Engine will run the operation in a BEGIN block if one is
not started already.
References: #4846
[engine] [deprecated] Deprecated the behavior by which a _schema.Column can be used as the key
in a result set row lookup, when that _schema.Column is not part of the
SQL selectable that is being selected; that is, it is only matched on name.
A deprecation warning is now emitted for this case. Various ORM use
cases, such as those involving _expression.text() constructs, have been improved
so that this fallback logic is avoided in most cases.
References: #4877
[engine] [deprecated] Deprecated remaining engine-level introspection and utility methods
including _engine.Engine.run_callable(), _engine.Engine.transaction(),
_engine.Engine.table_names(), _engine.Engine.has_table(). The utility
methods are superseded by modern context-manager patterns, and the table
introspection tasks are suited by the _reflection.Inspector object.
References: #4755
[engine] [removed] Remove deprecated method get_primary_keys in the Dialect and
_reflection.Inspector classes. Please refer to the
Dialect.get_pk_constraint() and _reflection.Inspector.get_primary_keys()
methods.
Remove deprecated event dbapi_error and the method
ConnectionEvents.dbapi_error. Please refer to the
_events.ConnectionEvents.handle_error() event.
This change also removes the attributes ExecutionContext.is_disconnect
and ExecutionContext.exception.
References: #4643
[engine] [removed] The internal dialect method Dialect.reflecttable has been removed. A
review of third party dialects has not found any making use of this method,
as it was already documented as one that should not be used by external
dialects. Additionally, the private Engine._run_visitor method
is also removed.
References: #4755
[engine] [removed] The long-deprecated Inspector.get_table_names.order_by parameter has
been removed.
References: #4755
[engine] [renamed] The _reflection.Inspector.reflecttable() was renamed to
_reflection.Inspector.reflect_table().
References: #5244

sql

[sql] [feature] Added "from linting" as a built-in feature to the SQL compiler. This
allows the compiler to maintain graph of all the FROM clauses in a
particular SELECT statement, linked by criteria in either the WHERE
or in JOIN clauses that link these FROM clauses together. If any two
FROM clauses have no path between them, a warning is emitted that the
query may be producing a cartesian product. As the Core expression
language as well as the ORM are built on an "implicit FROMs" model where
a particular FROM clause is automatically added if any part of the query
refers to it, it is easy for this to happen inadvertently and it is
hoped that the new feature helps with this issue.
References: #4737
[sql] [feature] [mssql] [oracle] Added new "post compile parameters" feature. This feature allows a
bindparam() construct to have its value rendered into the SQL string
before being passed to the DBAPI driver, but after the compilation step,
using the "literal render" feature of the compiler. The immediate
rationale for this feature is to support LIMIT/OFFSET schemes that don't
work or perform well as bound parameters handled by the database driver,
while still allowing for SQLAlchemy SQL constructs to be cacheable in their
compiled form. The immediate targets for the new feature are the "TOP
N" clause used by SQL Server (and Sybase) which does not support a bound
parameter, as well as the "ROWNUM" and optional "FIRST_ROWS()" schemes used
by the Oracle dialect, the former of which has been known to perform better
without bound parameters and the latter of which does not support a bound
parameter. The feature builds upon the mechanisms first developed to
support "expanding" parameters for IN expressions. As part of this
feature, the Oracle use_binds_for_limits feature is turned on
unconditionally and this flag is now deprecated.
References: #4808

[sql] [feature] Add support for regular expression on supported backends.
Two operations have been defined:

-   `_sql.ColumnOperators.regexp_match()` implementing a regular
    expression match like function.

-   `_sql.ColumnOperators.regexp_replace()` implementing a regular
    expression string replace function.

Supported backends include SQLite, PostgreSQL, MySQL / MariaDB, and Oracle.

References: #1390

[sql] [feature] The _expression.select() construct and related constructs now allow for
duplication of column labels and columns themselves in the columns clause,
mirroring exactly how column expressions were passed in. This allows
the tuples returned by an executed result to match what was SELECTed
for in the first place, which is how the ORM _query.Query works, so
this establishes better cross-compatibility between the two constructs.
Additionally, it allows column-positioning-sensitive structures such as
UNIONs (i.e. _selectable.CompoundSelect) to be more intuitively constructed
in those cases where a particular column might appear in more than one
place. To support this change, the _expression.ColumnCollection has been
revised to support duplicate columns as well as to allow integer index
access.
References: #4753
[sql] [feature] Enhanced the disambiguating labels feature of the
_expression.select() construct such that when a select statement
is used in a subquery, repeated column names from different tables are now
automatically labeled with a unique label name, without the need to use the
full "apply_labels()" feature that combines tablename plus column name.
The disambiguated labels are available as plain string keys in the .c
collection of the subquery, and most importantly the feature allows an ORM
_orm.aliased() construct against the combination of an entity and an
arbitrary subquery to work correctly, targeting the correct columns despite
same-named columns in the source tables, without the need for an "apply
labels" warning.
References: #5221
[sql] [feature] The "expanding IN" feature, which generates IN expressions at query
execution time which are based on the particular parameters associated with
the statement execution, is now used for all IN expressions made against
lists of literal values. This allows IN expressions to be fully cacheable
independently of the list of values being passed, and also includes support
for empty lists. For any scenario where the IN expression contains
non-literal SQL expressions, the old behavior of pre-rendering for each
position in the IN is maintained. The change also completes support for
expanding IN with tuples, where previously type-specific bind processors
weren't taking effect.
References: #4645
[sql] [feature] Along with the new transparent statement caching feature introduced as part
of #4369, a new feature intended to decrease the Python overhead
of creating statements is added, allowing lambdas to be used when
indicating arguments being passed to a statement object such as select(),
Query(), update(), etc., as well as allowing the construction of full
statements within lambdas in a similar manner as that of the "baked query"
system. The rationale of using lambdas is adapted from that of the "baked
query" approach which uses lambdas to encapsulate any amount of Python code
into a callable that only needs to be called when the statement is first
constructed into a string. The new feature however is more sophisticated
in that Python literal values that would be passed as parameters are
automatically extracted, so that there is no longer a need to use
bindparam() objects with such queries. Use of the feature is optional and
can be used to as small or as great a degree as is desired, while still
allowing statements to be fully cacheable.
References: #5380
[sql] [usecase] The Index.create() and Index.drop() methods now have a
parameter Index.create.checkfirst, in the same way as that of
_schema.Table and Sequence, which when enabled will cause the
operation to detect if the index exists (or not) before performing a create
or drop operation.
References: #527
[sql] [usecase] The true() and false() operators may now be applied as the
"onclause" of a _expression.join() on a backend that does not support
"native boolean" expressions, e.g. Oracle or SQL Server, and the expression
will render as "1=1" for true and "1=0" false. This is the behavior that
was introduced many years ago in #2804 for and/or expressions.
[sql] [usecase] Change the method __str of ColumnCollection to avoid
confusing it with a python list of string.
References: #5191
[sql] [usecase] Add support to FETCH {FIRST | NEXT} [ count ] {ROW | ROWS} {ONLY | WITH TIES} in the select for the supported
backends, currently PostgreSQL, Oracle and MSSQL.
References: #5576
[sql] [usecase] Additional logic has been added such that certain SQL expressions which
typically wrap a single database column will use the name of that column as
their "anonymous label" name within a SELECT statement, potentially making
key-based lookups in result tuples more intuitive. The primary example of
this is that of a CAST expression, e.g. CAST(table.colname AS INTEGER),
which will export its default name as "colname", rather than the usual
"anon_1" label, that is, CAST(table.colname AS INTEGER) AS colname.
If the inner expression doesn't have a name, then the previous "anonymous
label" logic is used. When using SELECT statements that make use of
_expression.Select.apply_labels(), such as those emitted by the ORM, the
labeling logic will produce <tablename>_<inner column name> in the same
was as if the column were named alone. The logic applies right now to the
cast() and type_coerce() constructs as well as some
single-element boolean expressions.
References: #4449
[sql] [change] The "clause coercion" system, which is SQLAlchemy Core's system of receiving
arguments and resolving them into _expression.ClauseElement structures in order
to build up SQL expression objects, has been rewritten from a series of
ad-hoc functions to a fully consistent class-based system. This change
is internal and should have no impact on end users other than more specific
error messages when the wrong kind of argument is passed to an expression
object, however the change is part of a larger set of changes involving
the role and behavior of _expression.select() objects.
References: #4617
[sql] [change] Added a core Values object that enables a VALUES construct
to be used in the FROM clause of an SQL statement for databases that
support it (mainly PostgreSQL and SQL Server).
References: #4868
[sql] [change] The _expression.select() construct is moving towards a new calling
form that is select(col1, col2, col3, ..), with all other keyword
arguments removed, as these are all suited using generative methods. The
single list of column or table arguments passed to select() is still
accepted, however is no longer necessary if expressions are passed in a
simple positional style. Other keyword arguments are disallowed when this
form is used.
References: #5284
[sql] [change] As part of the SQLAlchemy 2.0 migration project, a conceptual change has
been made to the role of the _expression.SelectBase class hierarchy,
which is the root of all "SELECT" statement constructs, in that they no
longer serve directly as FROM clauses, that is, they no longer subclass
_expression.FromClause. For end users, the change mostly means that any
placement of a _expression.select() construct in the FROM clause of another
_expression.select() requires first that it be wrapped in a subquery first,
which historically is through the use of the _expression.SelectBase.alias()
method, and is now also available through the use of
_expression.SelectBase.subquery(). This was usually a requirement in any
case since several databases don't accept unnamed SELECT subqueries
in their FROM clause in any case.
References: #4617
[sql] [change] Added a new Core class Subquery, which takes the place of
_expression.Alias when creating named subqueries against a _expression.SelectBase
object. Subquery acts in the same way as _expression.Alias
and is produced from the _expression.SelectBase.subquery() method; for
ease of use and backwards compatibility, the _expression.SelectBase.alias()
method is synonymous with this new method.
References: #4617
[sql] [performance] An all-encompassing reorganization and refactoring of Core and ORM
internals now allows all Core and ORM statements within the areas of
DQL (e.g. SELECTs) and DML (e.g. INSERT, UPDATE, DELETE) to allow their
SQL compilation as well as the construction of result-fetching metadata
to be fully cached in most cases. This effectively provides a transparent
and generalized version of what the "Baked Query" extension has offered
for the ORM in past versions. The new feature can calculate the
cache key for any given SQL construction based on the string that
it would ultimately produce for a given dialect, allowing functions that
compose the equivalent select(), Query(), insert(), update() or delete()
object each time to have that statement cached after it's generated
the first time.
The feature is enabled transparently but includes some new programming
paradigms that may be employed to make the caching even more efficient.
References: #4639
[sql] [bug] Fixed issue where when constructing constraints from ORM-bound columns,
primarily _schema.ForeignKey objects but also UniqueConstraint,
CheckConstraint and others, the ORM-level
InstrumentedAttribute is discarded entirely, and all ORM-level
annotations from the columns are removed; this is so that the constraints
are still fully pickleable without the ORM-level entities being pulled in.
These annotations are not necessary to be present at the schema/metadata
level.
References: #5001
[sql] [bug] Registered function names based on GenericFunction are now
retrieved in a case-insensitive fashion in all cases, removing the
deprecation logic from 1.3 which temporarily allowed multiple
GenericFunction objects to exist with differing cases. A
GenericFunction that replaces another on the same name whether or
not it's case sensitive emits a warning before replacing the object.
References: #4569, #4649
[sql] [bug] Creating an and_() or or_() construct with no arguments or
empty *args will now emit a deprecation warning, as the SQL produced is
a no-op (i.e. it renders as a blank string). This behavior is considered to
be non-intuitive, so for empty or possibly empty and_() or
or_() constructs, an appropriate default boolean should be included,
such as and_(True, *args) or or_(False, *args). As has been the
case for many major versions of SQLAlchemy, these particular boolean
values will not render if the *args portion is non-empty.
References: #5054
[sql] [bug] Improved the _sql.tuple_() construct such that it behaves predictably
when used in a columns-clause context. The SQL tuple is not supported as a
"SELECT" columns clause element on most backends; on those that do
(PostgreSQL, not surprisingly), the Python DBAPI does not have a "nested
type" concept so there are still challenges in fetching rows for such an
object. Use of _sql.tuple_() in a _sql.select() or
_orm.Query will now raise a _exc.CompileError at the
point at which the _sql.tuple_() object is seen as presenting itself
for fetching rows (i.e., if the tuple is in the columns clause of a
subquery, no error is raised). For ORM use,the _orm.Bundle object
is an explicit directive that a series of columns should be returned as a
sub-tuple per row and is suggested by the error message. Additionally ,the
tuple will now render with parenthesis in all contexts. Previously, the
parenthesization would not render in a columns context leading to
non-defined behavior.
References: #5127
[sql] [bug] [postgresql] Improved support for column names that contain percent signs in the string,
including repaired issues involving anoymous labels that also embedded a
column name with a percent sign in it, as well as re-established support
for bound parameter names with percent signs embedded on the psycopg2
dialect, using a late-escaping process similar to that used by the
cx_Oracle dialect.
References: #5653
[sql] [bug] Custom functions that are created as subclasses of
FunctionElement will now generate an "anonymous label" based on
the "name" of the function just like any other Function object,
e.g. "SELECT myfunc() AS myfunc_1". While SELECT statements no longer
require labels in order for the result proxy object to function, the ORM
still targets columns in rows by using objects as mapping keys, which works
more reliably when the column expressions have distinct names. In any
case, the behavior is now made consistent between functions generated by
func and those generated as custom FunctionElement
objects.
References: #4887
[sql] [bug] Reworked the _expression.ClauseElement.compare() methods in terms of a new
visitor-based approach, and additionally added test coverage ensuring that
all _expression.ClauseElement subclasses can be accurately compared
against each other in terms of structure. Structural comparison
capability is used to a small degree within the ORM currently, however
it also may form the basis for new caching features.
References: #4336
[sql] [bug] Deprecate usage of DISTINCT ON in dialect other than PostgreSQL.
Deprecate old usage of string distinct in MySQL dialect
References: #4002
[sql] [bug] The ORDER BY clause of a _selectable.CompoundSelect, e.g. UNION, EXCEPT, etc.
will not render the table name associated with a given column when applying
_selectable.CompoundSelect.order_by() in terms of a _schema.Table - bound
column. Most databases require that the names in the ORDER BY clause be
expressed as label names only which are matched to names in the first
SELECT statement. The change is related to #4617 in that a
previous workaround was to refer to the .c attribute of the
_selectable.CompoundSelect in order to get at a column that has no table
name. As the subquery is now named, this change allows both the workaround
to continue to work, as well as allows table-bound columns as well as the
_selectable.CompoundSelect.selected_columns collections to be usable in the
_selectable.CompoundSelect.order_by() method.
References: #4617
[sql] [bug] The _expression.Join construct no longer considers the "onclause" as a source
of additional FROM objects to be omitted from the FROM list of an enclosing
_expression.Select object as standalone FROM objects. This applies to an ON
clause that includes a reference to another FROM object outside the JOIN;
while this is usually not correct from a SQL perspective, it's also
incorrect for it to be omitted, and the behavioral change makes the
_expression.Select / _expression.Join behave a bit more intuitively.
References: #4621
[sql] [deprecated] The _sql.Join.alias() method is deprecated and will be removed in
SQLAlchemy 2.0. An explicit select + subquery, or aliasing of the inner
tables, should be used instead.
References: #5010
[sql] [deprecated] The _schema.Table class now raises a deprecation warning
when columns with the same name are defined. To replace a column a new
parameter _schema.Table.append_column.replace_existing was
added to the _schema.Table.append_column() method.
The _expression.ColumnCollection.contains_column() will now
raises an error when called with a string, suggesting the caller
to use in instead.
[sql] [removed] The "threadlocal" execution strategy, deprecated in 1.3, has been
removed for 1.4, as well as the concept of "engine strategies" and the
Engine.contextual_connect method. The "strategy='mock'" keyword
argument is still accepted for now with a deprecation warning; use
create_mock_engine() instead for this use case.
References: #4632
[sql] [removed] Removed the sqlalchemy.sql.visitors.iterate_depthfirst and
sqlalchemy.sql.visitors.traverse_depthfirst functions. These functions
were unused by any part of SQLAlchemy. The
_sa.sql.visitors.iterate() and _sa.sql.visitors.traverse()
functions are commonly used for these functions. Also removed unused
options from the remaining functions including "column_collections",
"schema_visitor".
[sql] [removed] Removed the concept of a bound engine from the Compiler object,
and removed the .execute() and .scalar() methods from
Compiler. These were essentially forgotten methods from over a
decade ago and had no practical use, and it's not appropriate for the
Compiler object itself to be maintaining a reference to an
_engine.Engine.
[sql] [removed] Remove deprecated methods Compiled.compile, ClauseElement.__and__ and
ClauseElement.__or__ and attribute Over.func.
Remove deprecated FromClause.count method. Please use the
_functions.count function available from the
func namespace.
References: #4643
[sql] [removed] Remove deprecated parameters text.bindparams and text.typemap.
Please refer to the _expression.TextClause.bindparams() and
_expression.TextClause.columns() methods.
Remove deprecated parameter Table.useexisting. Please use
_schema.Table.extend_existing.
References: #4643
[sql] [renamed] _schema.Table parameter mustexist has been renamed
to _schema.Table.must_exist and will now warn when used.
[sql] [renamed] The _expression.SelectBase.as_scalar() and _query.Query.as_scalar() methods have
been renamed to _expression.SelectBase.scalar_subquery() and
_query.Query.scalar_subquery(), respectively. The old names continue to
exist within 1.4 series with a deprecation warning. In addition, the
implicit coercion of _expression.SelectBase, _expression.Alias, and other
SELECT oriented objects into scalar subqueries when evaluated in a column
context is also deprecated, and emits a warning that the
_expression.SelectBase.scalar_subquery() method should be called explicitly.
This warning will in a later major release become an error, however the
message will always be clear when _expression.SelectBase.scalar_subquery() needs
to be invoked. The latter part of the change is for clarity and to reduce
the implicit decisionmaking by the query coercion system. The
Subquery.as_scalar() method, which was previously
Alias.as_scalar, is also deprecated; .scalar_subquery() should be
invoked directly from _expression.select()object or_query.Query` object.
This change is part of the larger change to convert _expression.select() objects
to no longer be directly part of the "from clause" class hierarchy, which
also includes an overhaul of the clause coercion system.
References: #4617

[sql] [renamed] Several operators are renamed to achieve more consistent naming across
SQLAlchemy.

The operator changes are:

-   `isfalse` is now `is_false`

-   `isnot_distinct_from` is now `is_not_distinct_from`

-   `istrue` is now `is_true`

-   `notbetween` is now `not_between`

-   `notcontains` is now `not_contains`

-   `notendswith` is now `not_endswith`

-   `notilike` is now `not_ilike`

-   `notlike` is now `not_like`

-   `notmatch` is now `not_match`

-   `notstartswith` is now `not_startswith`

-   `nullsfirst` is now `nulls_first`

-   `nullslast` is now `nulls_last`

-   `isnot` is now `is_not`

-   `not_in_` is now `not_in`

Because these are core operators, the internal migration strategy for this
change is to support legacy terms for an extended period of time -- if not
indefinitely -- but update all documentation, tutorials, and internal usage
to the new terms. The new terms are used to define the functions, and
the legacy terms have been deprecated into aliases of the new terms.

References: #5429, #5435

[sql] [postgresql] Allow specifying the data type when creating a Sequence in
PostgreSQL by using the parameter Sequence.data_type.
References: #5498
[sql] [reflection] The "NO ACTION" keyword for foreign key "ON UPDATE" is now considered to be
the default cascade for a foreign key on all supporting backends (SQlite,
MySQL, PostgreSQL) and when detected is not included in the reflection
dictionary; this is already the behavior for PostgreSQL and MySQL for all
previous SQLAlchemy versions in any case. The "RESTRICT" keyword is
positively stored when detected; PostgreSQL does report on this keyword,
and MySQL as of version 8.0 does as well. On earlier MySQL versions, it is
not reported by the database.
References: #4741
[sql] [reflection] Added support for reflecting "identity" columns, which are now returned
as part of the structure returned by _reflection.Inspector.get_columns().
When reflecting full _schema.Table objects, identity columns will
be represented using the _schema.Identity construct.
Currently the supported backends are
PostgreSQL >= 10, Oracle >= 12 and MSSQL (with different syntax
and a subset of functionalities).
References: #5324, #5527

schema

[schema] [change] The Enum.create_constraint and
Boolean.create_constraint parameters now default to False,
indicating when a so-called "non-native" version of these two datatypes is
created, a CHECK constraint will not be generated by default. These CHECK
constraints present schema-management maintenance complexities that should
be opted in to, rather than being turned on by default.
References: #5367
[schema] [bug] Cleaned up the internal str() for datatypes so that all types produce a
string representation without any dialect present, including that it works
for third-party dialect types without that dialect being present. The
string representation defaults to being the UPPERCASE name of that type
with nothing else.
References: #4262
[schema] [removed] Remove deprecated class Binary. Please use LargeBinary.
References: #4643
[schema] [renamed] Renamed the _schema.Table.tometadata() method to
_schema.Table.to_metadata(). The previous name remains with a
deprecation warning.
References: #5413
[schema] [sql] Added the _schema.Identity construct that can be used to
configure identity columns rendered with GENERATED { ALWAYS |
BY DEFAULT } AS IDENTITY. Currently the supported backends are
PostgreSQL >= 10, Oracle >= 12 and MSSQL (with different syntax
and a subset of functionalities).
References: #5324, #5360, #5362

extensions

[extensions] [usecase] Custom compiler constructs created using the sqlalchemy.ext.compiled
extension will automatically add contextual information to the compiler
when a custom construct is interpreted as an element in the columns
clause of a SELECT statement, such that the custom element will be
targetable as a key in result row mappings, which is the kind of targeting
that the ORM uses in order to match column elements into result tuples.
References: #4887
[extensions] [change] Added new parameter _automap.AutomapBase.prepare.autoload_with
which supersedes _automap.AutomapBase.prepare.reflect
and _automap.AutomapBase.prepare.engine.
References: #5142

postgresql

[postgresql] [usecase] Added support for PostgreSQL "readonly" and "deferrable" flags for all of
psycopg2, asyncpg and pg8000 dialects. This takes advantage of a newly
generalized version of the "isolation level" API to support other kinds of
session attributes set via execution options that are reliably reset
when connections are returned to the connection pool.
References: #5549
[postgresql] [usecase] The maximum buffer size for the BufferedRowResultProxy, which
is used by dialects such as PostgreSQL when stream_results=True, can
now be set to a number greater than 1000 and the buffer will grow to
that size. Previously, the buffer would not go beyond 1000 even if the
value were set larger. The growth of the buffer is also now based
on a simple multiplying factor currently set to 5. Pull request courtesy
Soumaya Mauthoor.
References: #4914
[postgresql] [change] When using the psycopg2 dialect for PostgreSQL, psycopg2 minimum version is
set at 2.7. The psycopg2 dialect relies upon many features of psycopg2
released in the past few years, so to simplify the dialect, version 2.7,
released in March, 2017 is now the minimum version required.
[postgresql] [performance] The psycopg2 dialect now defaults to using the very performant
execute_values() psycopg2 extension for compiled INSERT statements,
and also implements RETURNING support when this extension is used. This
allows INSERT statements that even include an autoincremented SERIAL
or IDENTITY value to run very fast while still being able to return the
newly generated primary key values. The ORM will then integrate this
new feature in a separate change.
References: #5401

[postgresql] [bug] The pg8000 dialect has been revised and modernized for the most recent
version of the pg8000 driver for PostgreSQL. Changes to the dialect
include:

-   All data types are now sent as text rather than binary.

-   Using adapters, custom types can be plugged in to pg8000.

-   Previously, named prepared statements were used for all statements.
    Now unnamed prepared statements are used by default, and named
    prepared statements can be used explicitly by calling the
    Connection.prepare() method, which returns a PreparedStatement
    object.

Pull request courtesy Tony Locke.

[postgresql] [deprecated] The pygresql and py-postgresql dialects are deprecated.
References: #5189
[postgresql] [removed] Remove support for deprecated engine URLs of the form postgres://;
this has emitted a warning for many years and projects should be
using postgresql://.
References: #4643

mysql

[mysql] [feature] Added support for MariaDB Connector/Python to the mysql dialect. Original
pull request courtesy Georg Richter.
References: #5459
[mysql] [usecase] Added a new dialect token "mariadb" that may be used in place of "mysql" in
the _sa.create_engine() URL. This will deliver a MariaDB dialect
subclass of the MySQLDialect in use that forces the "is_mariadb" flag to
True. The dialect will raise an error if a server version string that does
not indicate MariaDB in use is received. This is useful for
MariaDB-specific testing scenarios as well as to support applications that
are hardcoding to MariaDB-only concepts. As MariaDB and MySQL featuresets
and usage patterns continue to diverge, this pattern may become more
prominent.
References: #5496
[mysql] [usecase] Added support for use of the Sequence construct with MariaDB 10.3
and greater, as this is now supported by this database. The construct
integrates with the _schema.Table object in the same way that it does for
other databases like PostgreSQL and Oracle; if is present on the integer
primary key "autoincrement" column, it is used to generate defaults. For
backwards compatibility, to support a _schema.Table that has a
Sequence on it to support sequence only databases like Oracle,
while still not having the sequence fire off for MariaDB, the optional=True
flag should be set, which indicates the sequence should only be used to
generate the primary key if the target database offers no other option.
References: #4976
[mysql] [bug] The MySQL and MariaDB dialects now query from the information_schema.tables
system view in order to determine if a particular table exists or not.
Previously, the "DESCRIBE" command was used with an exception catch to
detect non-existent, which would have the undesirable effect of emitting a
ROLLBACK on the connection. There appeared to be legacy encoding issues
which prevented the use of "SHOW TABLES", for this, but as MySQL support is
now at 5.0.2 or above due to #4189, the information_schema tables
are now available in all cases.
[mysql] [bug] The "skip_locked" keyword used with with_for_update() will render "SKIP
LOCKED" on all MySQL backends, meaning it will fail for MySQL less than
version 8 and on current MariaDB backends. This is because those backends
do not support "SKIP LOCKED" or any equivalent, so this error should not be
silently ignored. This is upgraded from a warning in the 1.3 series.
References: #5568
[mysql] [bug] MySQL dialect's server_version_info tuple is now all numeric. String
tokens like "MariaDB" are no longer present so that numeric comparison
works in all cases. The .is_mariadb flag on the dialect should be
consulted for whether or not mariadb was detected. Additionally removed
structures meant to support extremely old MySQL versions 3.x and 4.x;
the minimum MySQL version supported is now version 5.0.2.
References: #4189
[mysql] [deprecated] The OurSQL dialect is deprecated.
References: #5189
[mysql] [removed] Remove deprecated dialect mysql+gaerdbms that has been deprecated
since version 1.0. Use the MySQLdb dialect directly.
Remove deprecated parameter quoting from mysql.ENUM
and mysql.SET in the mysql dialect. The values passed to the
enum or the set are quoted by SQLAlchemy when needed automatically.
References: #4643

sqlite

[sqlite] [change] Dropped support for right-nested join rewriting to support old SQLite
versions prior to 3.7.16, released in 2013. It is expected that
all modern Python versions among those now supported should all include
much newer versions of SQLite.
References: #4895

mssql

[mssql] [feature] [sql] Added support for the _types.JSON datatype on the SQL Server
dialect using the _mssql.JSON implementation, which implements SQL
Server's JSON functionality against the NVARCHAR(max) datatype as per
SQL Server documentation. Implementation courtesy Gord Thompson.
References: #4384
[mssql] [feature] Added support for "CREATE SEQUENCE" and full Sequence support for
Microsoft SQL Server. This removes the deprecated feature of using
Sequence objects to manipulate IDENTITY characteristics which
should now be performed using mssql_identity_start and
mssql_identity_increment as documented at mssql_identity. The
change includes a new parameter Sequence.data_type to
accommodate SQL Server's choice of datatype, which for that backend
includes INTEGER, BIGINT, and DECIMAL(n, 0). The default starting value
for SQL Server's version of Sequence has been set at 1; this
default is now emitted within the CREATE SEQUENCE DDL for all backends.
References: #4235, #4633
[mssql] [usecase] [postgresql] [reflection] [schema] Improved support for covering indexes (with INCLUDE columns). Added the
ability for postgresql to render CREATE INDEX statements with an INCLUDE
clause from Core. Index reflection also report INCLUDE columns separately
for both mssql and postgresql (11+).
References: #4458
[mssql] [usecase] [postgresql] Added support for inspection / reflection of partial indexes / filtered
indexes, i.e. those which use the mssql_where or postgresql_where
parameters, with _schema.Index. The entry is both part of the
dictionary returned by Inspector.get_indexes() as well as part of a
reflected _schema.Index construct that was reflected. Pull
request courtesy Ramon Williams.
References: #4966
[mssql] [usecase] [reflection] Added support for reflection of temporary tables with the SQL Server dialect.
Table names that are prefixed by a pound sign "#" are now introspected from
the MSSQL "tempdb" system catalog.
References: #5506
[mssql] [change] SQL Server OFFSET and FETCH keywords are now used for limit/offset, rather
than using a window function, for SQL Server versions 11 and higher. TOP is
still used for a query that features only LIMIT. Pull request courtesy
Elkin.
References: #5084
[mssql] [bug] [schema] Fixed an issue where _reflection.has_table() always returned
False for temporary tables.
References: #5597
[mssql] [bug] Fixed the base class of the _mssql.DATETIMEOFFSET datatype to
be based on the DateTime class hierarchy, as this is a
datetime-holding datatype.
References: #4980
[mssql] [deprecated] The adodbapi and mxODBC dialects are deprecated.
References: #5189
[mssql] The mssql dialect will assume that at least MSSQL 2005 is used.
There is no hard exception raised if a previous version is detected,
but operations may fail for older versions.
[mssql] [reflection] As part of the support for reflecting _schema.Identity objects,
the method _reflection.Inspector.get_columns() no longer returns
mssql_identity_start and mssql_identity_increment as part of the
dialect_options. Use the information in the identity key instead.
References: #5527
[mssql] [engine] Deprecated the legacy_schema_aliasing parameter to
_sa.create_engine(). This is a long-outdated parameter that has
defaulted to False since version 1.1.
References: #4809

oracle

[oracle] [usecase] The max_identifier_length for the Oracle dialect is now 128 characters by
default, unless compatibility version less than 12.2 upon first connect, in
which case the legacy length of 30 characters is used. This is a
continuation of the issue as committed to the 1.3 series which adds max
identifier length detection upon first connect as well as warns for the
change in Oracle server.
References: #4857
[oracle] [change] The LIMIT / OFFSET scheme used in Oracle now makes use of named subqueries
rather than unnamed subqueries when it transparently rewrites a SELECT
statement to one that uses a subquery that includes ROWNUM. The change is
part of a larger change where unnamed subqueries are no longer directly
supported by Core, as well as to modernize the internal use of the select()
construct within the Oracle dialect.
[oracle] [bug] Correctly render _schema.Sequence and _schema.Identity
column options nominvalue and nomaxvalue as NOMAXVALUE and
``NOMINVALUE` on oracle database.
[oracle] [bug] The _oracle.INTERVAL class of the Oracle dialect is now correctly
a subclass of the abstract version of Interval as well as the
correct "emulated" base class, which allows for correct behavior under both
native and non-native modes; previously it was only based on
TypeEngine.
References: #4971

firebird

[firebird] [deprecated] The Firebird dialect is deprecated, as there is now a 3rd party
dialect that supports this database.
References: #5189

misc

[misc] [deprecated] The Sybase dialect is deprecated.
References: #5189

sqlalchemy/sqlalchemy rel_1_4_0b1 1.4.0b1 on GitHub