1.5.6

Released: March 5, 2021

bug

• [bug] [mssql] [operations] Fixed bug where the "existing_type" parameter, which the MSSQL dialect
  requires in order to change the nullability of a column in the absence of
  also changing the column type, would cause an ALTER COLUMN operation to
  incorrectly render a second ALTER statement without the nullability if a
  new type were also present, as the MSSQL-specific contract did not
  anticipate all three of "nullability", "type_" and "existing_type" being
  sent at the same time.

  References: #812

misc

• [template] Add async template to Alembic to bootstrap environments that use
  async DBAPI. Updated the cookbook to include a migration guide
  on how to adapt an existing enviroment for use with DBAPI drivers.