batch alter operations won't add server_default

[sqlalchemy-bot]

Migrated issue, originally created by Anthony Ryan (@anthonyryan1)

server_default doesn't seem to work on batch alter operations. Tested on sqlite3.

Minimal test case

Prepare test table

def upgrade():
    op.create_table(
      'test',
      sa.Column('integer', sa.Integer, nullable=False, primary_key=True),
      sa.Column('string', sa.Text, nullable=False),
    )

Set a column default value

def upgrade():
    with op.batch_alter_table('test') as batch_op:
        batch_op.alter_column('string', server_default='default')

Expected result

CREATE TABLE test (
        integer INTEGER NOT NULL, 
        string TEXT DEFAULT 'default' NOT NULL, 
        PRIMARY KEY (integer)
);

Actual result

CREATE TABLE test (
        integer INTEGER NOT NULL, 
        string TEXT NOT NULL, 
        PRIMARY KEY (integer)
);

[sqlalchemy-bot]

Changes by Anthony Ryan (@anthonyryan1):

• edited description

[sqlalchemy-bot]

Changes by Anthony Ryan (@anthonyryan1):

• edited description

[sqlalchemy-bot]

Changes by Anthony Ryan (@anthonyryan1):

• edited description

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

potential fix, if you care to test:

diff --git a/alembic/operations/batch.py b/alembic/operations/batch.py
index 769cd92..369d08d 100644
--- a/alembic/operations/batch.py
+++ b/alembic/operations/batch.py
@@ -265,7 +265,7 @@ class ApplyBatchImpl(object):
         if nullable is not None:
             existing.nullable = nullable
         if server_default is not False:
-            existing.server_default = server_default
+            sql_schema.DefaultClause(server_default)._set_parent(existing)
         if autoincrement is not None:
             existing.autoincrement = bool(autoincrement)
 

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• set milestone to "fasttrack"

[sqlalchemy-bot]

Anthony Ryan (@anthonyryan1) wrote:

Hello Mike,

Thank you for the very fast response. I can confirm that patch seems to resolve my issue.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

• Fixed bug where the server_default parameter of alter_column()
  would not function correctly in batch mode.
  fixes batch alter operations won't add server_default #338

→ 3105ed6

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• changed status to closed

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

great thanks for checking that !