Summary

Fix ChangeField failure with index+column type changes on MySQL.

Review Request #14922 — Created March 17, 2026 and updated June 4, 2026, 2:01 p.m.

Information

Owner

david

Repository

Django Evolution

Branch

master

Bugs

Depends On

Reviewers

Groups

django-evolution

People

Description

When a ChangeField mutation changes both the field type and
unique/db_index attributes, MySQL's MODIFY COLUMN runs before the
index is dropped. MySQL rejects this for TEXT or BLOB columns with
the error "BLOB/TEXT column used in key specification without a key
length".

This happened because ChangeField.mutate() returns early after
change_column_type() when change_column_type_sets_attrs is True
(MySQL), skipping the change_column_attrs() call that handles index
drops.

change_column_type() now processes db_index/unique changes from
new_attrs when change_column_type_sets_attrs is True, emitting
index drops as pre-SQL (before the MODIFY) and index adds as post-SQL
(after). The SQLite3 backend also calls the new helper to keep in-memory
database state in sync.

Testing Done


Ran unit tests without the fix and verified that the new tests failed with

  the same issue I saw in the wild.
Ran unit tests with the fix and verified that it was now fixed.
Ran dbtests for mysql, sqlite, and postgresql.
Verified that this fixes the upgrade issue I was running into.

Commits

Summary	ID
Fix ChangeField failure with index+column type changes on MySQL. When a `ChangeField` mutation changes both the field type and `unique`/`db_index` attributes, MySQL's `MODIFY COLUMN` runs before the index is dropped. MySQL rejects this for `TEXT` or `BLOB` columns with the error "BLOB/TEXT column used in key specification without a key length". This happened because `ChangeField.mutate()` returns early after `change_column_type()` when `change_column_type_sets_attrs` is `True` (MySQL), skipping the `change_column_attrs()` call that handles index drops. `change_column_type()` now processes `db_index`/`unique` changes from `new_attrs` when `change_column_type_sets_attrs` is `True`, emitting index drops as pre-SQL (before the `MODIFY`) and index adds as post-SQL (after). The SQLite3 backend also calls the new helper to keep in-memory database state in sync. Testing Done: - Ran unit tests without the fix and verified that the new tests failed with the same issue I saw in the wild. - Ran unit tests with the fix and verified that it was now fixed. - Ran dbtests for mysql, sqlite, and postgresql. - Verified that this fixes the upgrade issue I was running into.	qnonyqrrwwqqowzwqpqlwpvvslzxpvum

Summary

Fix ChangeField failure with index+column type changes on MySQL.

When a `ChangeField` mutation changes both the field type and `unique`/`db_index` attributes, MySQL's `MODIFY COLUMN` runs before the index is dropped. MySQL rejects this for `TEXT` or `BLOB` columns with the error "BLOB/TEXT column used in key specification without a key length". This happened because `ChangeField.mutate()` returns early after `change_column_type()` when `change_column_type_sets_attrs` is `True` (MySQL), skipping the `change_column_attrs()` call that handles index drops. `change_column_type()` now processes `db_index`/`unique` changes from `new_attrs` when `change_column_type_sets_attrs` is `True`, emitting index drops as pre-SQL (before the `MODIFY`) and index adds as post-SQL (after). The SQLite3 backend also calls the new helper to keep in-memory database state in sync. Testing Done: - Ran unit tests without the fix and verified that the new tests failed with the same issue I saw in the wild. - Ran unit tests with the fix and verified that it was now fixed. - Ran dbtests for mysql, sqlite, and postgresql. - Verified that this fixes the upgrade issue I was running into.

qnonyqrrwwqqowzwqpqlwpvvslzxpvum

Issues

Description	From	Last Updated
Testing doesn't say, but I assume this also fixed the issue found in the wild?	chipx86	June 4, 2026, 9:19 a.m.
continuation line over-indented for visual indent Column: 48 Error code: E127	reviewbot	March 17, 2026, 4:45 p.m.
Versions are listed in descending order.	chipx86	June 4, 2026, 9:20 a.m.
Mind breaking the "This is necessary" into a new paragraph? There's a lot to process in this paragraph.	chipx86	June 4, 2026, 9:20 a.m.
This function has the following possible states: Old column New column Result Unique Unique No change Unique Indexed Remove unique, …	chipx86	June 4, 2026, 1:52 p.m.
Can we pull database_state out? This is used multiple times.	chipx86	June 4, 2026, 9:21 a.m.
Can you use keyword arguments here?	chipx86	June 4, 2026, 9:21 a.m.
Can you use keyword arguments here? I have no idea what True or None relate to.	chipx86	June 4, 2026, 9:21 a.m.

flake8 failed.

JSHint passed.

flake8

django_evolution/db/common.py (Diff revision 1)
The issue has been dropped. Show all issues
```
continuation line over-indented for visual indent

Column: 48
Error code: E127
```

Commits:

	Summary	ID
	Fix ChangeField failure with index+column type changes on MySQL. When a `ChangeField` mutation changes both the field type and `unique`/`db_index` attributes, MySQL's `MODIFY COLUMN` runs before the index is dropped. MySQL rejects this for `TEXT` or `BLOB` columns with the error "BLOB/TEXT column used in key specification without a key length". This happened because `ChangeField.mutate()` returns early after `change_column_type()` when `change_column_type_sets_attrs` is `True` (MySQL), skipping the `change_column_attrs()` call that handles index drops. `change_column_type()` now processes `db_index`/`unique` changes from `new_attrs` when `change_column_type_sets_attrs` is `True`, emitting index drops as pre-SQL (before the `MODIFY`) and index adds as post-SQL (after). The SQLite3 backend also calls the new helper to keep in-memory database state in sync. Testing Done: - Ran unit tests without the fix and verified that the new tests failed with the same issue I saw in the wild. - Ran unit tests with the fix and verified that it was now fixed. - Ran dbtests for mysql, sqlite, and postgresql.	qnonyqrrwwqqowzwqpqlwpvvslzxpvum
	Fix ChangeField failure with index+column type changes on MySQL. When a `ChangeField` mutation changes both the field type and `unique`/`db_index` attributes, MySQL's `MODIFY COLUMN` runs before the index is dropped. MySQL rejects this for `TEXT` or `BLOB` columns with the error "BLOB/TEXT column used in key specification without a key length". This happened because `ChangeField.mutate()` returns early after `change_column_type()` when `change_column_type_sets_attrs` is `True` (MySQL), skipping the `change_column_attrs()` call that handles index drops. `change_column_type()` now processes `db_index`/`unique` changes from `new_attrs` when `change_column_type_sets_attrs` is `True`, emitting index drops as pre-SQL (before the `MODIFY`) and index adds as post-SQL (after). The SQLite3 backend also calls the new helper to keep in-memory database state in sync. Testing Done: - Ran unit tests without the fix and verified that the new tests failed with the same issue I saw in the wild. - Ran unit tests with the fix and verified that it was now fixed. - Ran dbtests for mysql, sqlite, and postgresql.	qnonyqrrwwqqowzwqpqlwpvvslzxpvum

Diff:

Revision 2 (+712)

Show changes

	django_evolution/db/common.py
	django_evolution/db/sqlite3.py
	django_evolution/tests/test_change_field.py
	django_evolution/tests/db/mysql.py
	django_evolution/tests/db/postgresql.py
	django_evolution/tests/db/sqlite3.py

Checks run (2 succeeded)

flake8 passed.

JSHint passed.

This seems like the right approach. Went through the logic carefully and have some notes mostly to help ensure no future issues.

The issue has been resolved. Show all issues

Testing doesn't say, but I assume this also fixed the issue found in the wild?

david

June 4, 2026, 2:01 p.m.
```
Correct.
```

django_evolution/db/common.py (Diff revision 2)
The issue has been resolved. Show all issues
```
Versions are listed in descending order.
```

django_evolution/db/common.py (Diff revision 2)

The issue has been resolved. Show all issues

Mind breaking the "This is necessary" into a new paragraph? There's a lot to process in this paragraph.

django_evolution/db/common.py (Diff revision 2)

The issue has been resolved. Show all issues

This function has the following possible states:

Old column	New column	Result
Unique	Unique	No change
Unique	Indexed	Remove unique, add index
Unique	Non-indexed/unique	Remove unique
Unique (missing index)	Unique	No change
Unique (missing index)	Indexed	Create index
Unique (missing index)	Non-indexed/unique	No change
Indexed	Unique	Drop index, add unique
Indexed	Indexed	No change
Indexed	Non-indexed/unique	Drop index
Non-indexed/unique	Unique	Add unique
Non-indexed/unique	Indexed	Add index
Non-indexed/unique	Non-indexed/unique	No change

I think I have that right.

Some of these are implicitly covered by other tests, but we should ensure we have tests covering all combinations of unique/indexed states so there are no surprises now or as code evolves.

It would also be great to have a truth table like this in the code showing the expectations for future us.

Notable above, the "Unique (missing index) -> Unique" does nothing, which is probably right, but perhaps worth calling out because it won't result in a database index being installed.

django_evolution/db/common.py (Diff revision 2)
The issue has been resolved. Show all issues
```
Can we pull database_state out? This is used multiple times.
```
django_evolution/db/common.py (Diff revision 2)
The issue has been resolved. Show all issues
```
Can you use keyword arguments here?
```

django_evolution/db/common.py (Diff revision 2)

The issue has been resolved. Show all issues

Can you use keyword arguments here? I have no idea what True or None relate to.

Testing Done:

		Ran unit tests without the fix and verified that the new tests failed with the same issue I saw in the wild.
		Ran unit tests with the fix and verified that it was now fixed.
		Ran dbtests for mysql, sqlite, and postgresql.
	+	Verified that this fixes the upgrade issue I was running into.

Commits:

	Summary	ID
	Fix ChangeField failure with index+column type changes on MySQL. When a `ChangeField` mutation changes both the field type and `unique`/`db_index` attributes, MySQL's `MODIFY COLUMN` runs before the index is dropped. MySQL rejects this for `TEXT` or `BLOB` columns with the error "BLOB/TEXT column used in key specification without a key length". This happened because `ChangeField.mutate()` returns early after `change_column_type()` when `change_column_type_sets_attrs` is `True` (MySQL), skipping the `change_column_attrs()` call that handles index drops. `change_column_type()` now processes `db_index`/`unique` changes from `new_attrs` when `change_column_type_sets_attrs` is `True`, emitting index drops as pre-SQL (before the `MODIFY`) and index adds as post-SQL (after). The SQLite3 backend also calls the new helper to keep in-memory database state in sync. Testing Done: - Ran unit tests without the fix and verified that the new tests failed with the same issue I saw in the wild. - Ran unit tests with the fix and verified that it was now fixed. - Ran dbtests for mysql, sqlite, and postgresql.	qnonyqrrwwqqowzwqpqlwpvvslzxpvum
	Fix ChangeField failure with index+column type changes on MySQL. When a `ChangeField` mutation changes both the field type and `unique`/`db_index` attributes, MySQL's `MODIFY COLUMN` runs before the index is dropped. MySQL rejects this for `TEXT` or `BLOB` columns with the error "BLOB/TEXT column used in key specification without a key length". This happened because `ChangeField.mutate()` returns early after `change_column_type()` when `change_column_type_sets_attrs` is `True` (MySQL), skipping the `change_column_attrs()` call that handles index drops. `change_column_type()` now processes `db_index`/`unique` changes from `new_attrs` when `change_column_type_sets_attrs` is `True`, emitting index drops as pre-SQL (before the `MODIFY`) and index adds as post-SQL (after). The SQLite3 backend also calls the new helper to keep in-memory database state in sync. Testing Done: - Ran unit tests without the fix and verified that the new tests failed with the same issue I saw in the wild. - Ran unit tests with the fix and verified that it was now fixed. - Ran dbtests for mysql, sqlite, and postgresql. - Verified that this fixes the upgrade issue I was running into.	qnonyqrrwwqqowzwqpqlwpvvslzxpvum

Diff:

Revision 3 (+2962 -2)

Show changes

	django_evolution/db/common.py
	django_evolution/db/sqlite3.py
	django_evolution/tests/test_change_field.py
	django_evolution/tests/db/mysql.py
	django_evolution/tests/db/postgresql.py
	django_evolution/tests/db/sqlite3.py

Checks run (2 succeeded)

flake8 passed.

JSHint passed.