#29391: Postgres array lookups need to call get_db_prep_value to adapt values to
their db representation (FieldGetDbPrepValueMixin)
--------------------------------------------+------------------------
               Reporter:  Gavin Wahl        |          Owner:  (none)
                   Type:  Uncategorized     |         Status:  new
              Component:  contrib.postgres  |        Version:  2.0
               Severity:  Normal            |       Keywords:
           Triage Stage:  Unreviewed        |      Has patch:  0
    Needs documentation:  0                 |    Needs tests:  0
Patch needs improvement:  0                 |  Easy pickings:  0
                  UI/UX:  0                 |
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 I have have a model that has an ArrayField of objects that need to be
 adapted to database values (EnumField from https://github.com/hzdg/django-
 enumfields).

 The custom array lookups in django.contrib.postgres.arrays are not
 correctly calling the base fields get_db_prep_value/get_prep_value before
 passing the objects to the db api.

 Repro:

 {{{#!python
 import enum

 from django.db import models
 from django.contrib.postgres.fields import ArrayField


 class TestEnum(enum.Enum):
     VALUE_1 = 'value_1'


 class EnumField(models.CharField):
     def get_prep_value(self, value):
         if value is None:
             return None
         else:
             return value.value


 class TestModel(models.Model):
     array_of_enums = ArrayField(EnumField(max_length=20))


 TestModel.objects.filter(array_of_enums__contains=[TestEnum.VALUE_1])
 }}}

 Currently this fails with:

 {{{
 Traceback (most recent call last):
   File "django/db/backends/utils.py", line 64, in execute
     return self.cursor.execute(sql, params)
 psycopg2.ProgrammingError: can't adapt type 'TestEnum'

 The above exception was the direct cause of the following exception:

 Traceback (most recent call last):
   File "<console>", line 1, in <module>
   File "django/db/models/query.py", line 226, in __repr__
     data = list(self[:REPR_OUTPUT_SIZE + 1])
   File "django/db/models/query.py", line 250, in __iter__
     self._fetch_all()
   File "django/db/models/query.py", line 1118, in _fetch_all
     self._result_cache = list(self._iterable_class(self))
   File "django/db/models/query.py", line 53, in __iter__
     results = compiler.execute_sql(chunked_fetch=self.chunked_fetch)
   File "django/db/models/sql/compiler.py", line 899, in execute_sql
     raise original_exception
   File "django/db/models/sql/compiler.py", line 889, in execute_sql
     cursor.execute(sql, params)
   File "django/db/backends/utils.py", line 79, in execute
     return super(CursorDebugWrapper, self).execute(sql, params)
   File "django/db/backends/utils.py", line 64, in execute
     return self.cursor.execute(sql, params)
   File "django/db/utils.py", line 94, in __exit__
     six.reraise(dj_exc_type, dj_exc_value, traceback)
   File "django/utils/six.py", line 685, in reraise
     raise value.with_traceback(tb)
   File "django/db/backends/utils.py", line 64, in execute
     return self.cursor.execute(sql, params)
 django.db.utils.ProgrammingError: can't adapt type 'TestEnum'
 }}}

 I expect it to succeed and generate a WHERE clause of `array_of_enums @>
 ARRAY['value_1']`.

 I think the fix is just to have the lookups inherit from
 `FieldGetDbPrepValueMixin`.

-- 
Ticket URL: <https://code.djangoproject.com/ticket/29391>
Django <https://code.djangoproject.com/>
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