Add support for a USING clause when altering a column's type in PostgreSQL

[sqlalchemy-bot]

Migrated issue, originally created by Wouter Bolsterlee (@wbolster)

When changing a column's type, it is sometimes necessary to specify how to convert the existing value into a value of the new type. This is done using the USING clause of the SET DATA TYPE clause of the ALTER TABLE statement. See http://www.postgresql.org/docs/9.4/static/sql-altertable.html for details.

Currently it seems impossible to specify the USING clause using Alembic's op. alter_column(). It would be great if something like alter_column(using="convert_from(data, 'utf-8')::jsonb") would work.

[sqlalchemy-bot]

Changes by Wouter Bolsterlee (@wbolster):

• changed title from "Add support for a ALTER COLUMN USING ... in Postgr" to "Add support for a USING clause when altering a col"

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

it would be called postgresql_using. I can accept this as a PR which would alter the alembic/ddl/postgresql.py dialect to support this flag, in a similar way as something like "mssql_drop_foreign" in alembic/ddl/mssql.py.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

Support USING for Postgresql ALTER COLUMN.

Added support for the USING clause to the ALTER COLUMN operation
for Postgresql. Support is via the
:paramref:.op.alter_column.postgresql_using
parameter.

Fixes: #292
Change-Id: I8b1d418df0b6b731a68614dbffd7a9fb13de4de5
Pull-request: zzzeek/alembic#27

→ 84b9298

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• changed status to closed

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

Issue #39 was marked as a duplicate of this issue.