Opened 2 years ago
Closed 2 years ago
#34027 closed Bug (fixed)
Changing CharField type referenced by ForeignKey crashes on PostgreSQL.
Reported by: | Chris | Owned by: | David Sanders |
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Component: | Migrations | Version: | 4.1 |
Severity: | Normal | Keywords: | PostgreSQL |
Cc: | Triage Stage: | Ready for checkin | |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
When a ForeignKey
points to CharField
, and the CharField
is then changed to e.g. an AutoField
, the migration fails with:
psycopg2.errors.DatatypeMismatch: operator class "varchar_pattern_ops" does not accept data type bigint
The reason seems to be that the original ForeignKey
column in the database was a varchar
, and Django created a varchar_pattern_ops
index for it (e.g. one of those ..._like
indexes). Changing the column type to bigint
is not accepted by this index.
Manually dropping the index before attempting to run the migrations results in the migration being performed successfully.
Performing the same set of migrations on SQLite and on MySQL does not result in an error, it only fails on PostgreSQL.
Test case:
- Use models.py:
class ModelA(models.Model): # Custom CharField primary key id = models.CharField(max_length=10, primary_key=True) class ModelB(models.Model): modela = models.ForeignKey(ModelA, on_delete=models.CASCADE)
- Run
makemigrations
andmigrate
commands - Alter
ModelA
:class ModelA(models.Model): # No more custom primary key pass
- Run
makemigrations
andmigrate
commands again - Observe error on PostgreSQL, success on SQLite and MySQL
- Manually
DROP
the<applabel>_modelb_modela_id_<...>_like
index in PostgreSQL - Again run the
migrate
command - Now the migration succeeds
The problem is apparently that the BaseDatabaseSchemaEditor._alter_field()
method simply calls _alter_column_type_sql()
or _alter_column_collation_sql()
to directly change the column type of relations pointing to the field. These methods do not generate any additional SQL related to indexes etc as the normal (PostgreSQL version of) _alter_field
method would under similar circumstances. Note that the ..._like
index for the primary key itself _is_ dropped.
Similarly also, if the primary key field is changed in the other direction, e.g. from AutoField
to CharField
, the ..._like
index is not added to the existing ForeignKey
, it is only added for the primary key field, as it normally is when an integer field is changed to a text field.
Possibly related issues: #27338 #27860
Reported for version 3.2 but also observed on 4.1.
Change History (6)
comment:1 by , 2 years ago
Owner: | changed from | to
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Status: | new → assigned |
Version: | 3.2 → 4.1 |
comment:3 by , 2 years ago
Has patch: | set |
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comment:4 by , 2 years ago
Summary: | When ForeignKey target field type is changed from CharField to IntegerField, varchar_pattern_ops index is not dropped on PostgreSQL and migration fails → Changing CharField type referenced by ForeignKey crashes on PostgreSQL. |
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Triage Stage: | Unreviewed → Accepted |
comment:5 by , 2 years ago
Triage Stage: | Accepted → Ready for checkin |
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PR: https://github.com/django/django/pull/16087