Dev-iL opened a new pull request, #59739:
URL: https://github.com/apache/airflow/pull/59739
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Related: #59218
## Description:
This PR fixes a schema inconsistency that occurs on MySQL after running
database migrations.
## Problem
The `test_database_schema_and_sqlalchemy_model_are_in_sync` test fails on
MySQL with:
```none
Diff: [('modify_nullable', None, 'dag', 'is_stale', {'existing_type':
TINYINT(display_width=1), 'existing_server_default': False, 'existing_comment':
None}, True, False)]
```
The SQLAlchemy model defines `is_stale: Mapped[bool]` (non-nullable), but
after migration 0067 runs on MySQL, the column remains `nullable=True`.
## Root Cause
When using alembic's `batch_alter_table` with `alter_column` to rename a
column on MySQL, the nullability constraint is not properly preserved or set.
The original `is_active column` was created as `nullable=True` in the squashed
migration, and simply renaming it doesn't change that. With SQLAlchemy 2.0,
this behavior becomes more apparent as the schema comparison correctly detects
the mismatch between the database schema and the ORM model.
## Solution
Use raw `SQL ALTER TABLE ... CHANGE COLUMN` for MySQL to explicitly rename
the column and set `NOT NULL` in one atomic operation:
```sql
ALTER TABLE dag CHANGE COLUMN is_active is_stale TINYINT(1) NOT NULL
```
The fix also ensures any existing `NULL` values are handled before the
constraint is applied.
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