Refs #12990 -- Moved CheckFieldDefaultMixin to the django.db.models.fields.mixins.

django/contrib/postgres/fields/array.py

@@ -5,11 +5,11 @@ from django.contrib.postgres.forms import SimpleArrayField
 from django.contrib.postgres.validators import ArrayMaxLengthValidator
 from django.core import checks, exceptions
 from django.db.models import Field, IntegerField, Transform
+from django.db.models.fields.mixins import CheckFieldDefaultMixin
 from django.db.models.lookups import Exact, In
 from django.utils.translation import gettext_lazy as _
 
 from ..utils import prefix_validation_error
-from .mixins import CheckFieldDefaultMixin
 from .utils import AttributeSetter
 
 __all__ = ['ArrayField']

django/contrib/postgres/fields/hstore.py

@@ -4,10 +4,9 @@ from django.contrib.postgres import forms, lookups
 from django.contrib.postgres.fields.array import ArrayField
 from django.core import exceptions
 from django.db.models import Field, TextField, Transform
+from django.db.models.fields.mixins import CheckFieldDefaultMixin
 from django.utils.translation import gettext_lazy as _
 
-from .mixins import CheckFieldDefaultMixin
-
 __all__ = ['HStoreField']
 
 

django/contrib/postgres/fields/jsonb.py

@@ -7,10 +7,9 @@ from django.core import exceptions
 from django.db.models import (
     Field, TextField, Transform, lookups as builtin_lookups,
 )
+from django.db.models.fields.mixins import CheckFieldDefaultMixin
 from django.utils.translation import gettext_lazy as _
 
-from .mixins import CheckFieldDefaultMixin
-
 __all__ = ['JSONField']
 
 

django/contrib/postgres/fields/mixins.py

@@ -1,29 +0,0 @@
-from django.core import checks
-
-
-class CheckFieldDefaultMixin:
-    _default_hint = ('<valid default>', '<invalid default>')
-
-    def _check_default(self):
-        if self.has_default() and self.default is not None and not callable(self.default):
-            return [
-                checks.Warning(
-                    "%s default should be a callable instead of an instance so "
-                    "that it's not shared between all field instances." % (
-                        self.__class__.__name__,
-                    ),
-                    hint=(
-                        'Use a callable instead, e.g., use `%s` instead of '
-                        '`%s`.' % self._default_hint
-                    ),
-                    obj=self,
-                    id='postgres.E003',
-                )
-            ]
-        else:
-            return []
-
-    def check(self, **kwargs):
-        errors = super().check(**kwargs)
-        errors.extend(self._check_default())
-        return errors

django/db/models/fields/mixins.py

@@ -1,3 +1,5 @@
+from django.core import checks
+
 NOT_PROVIDED = object()
 
 
@@ -24,3 +26,31 @@ class FieldCacheMixin:
 
     def delete_cached_value(self, instance):
         del instance._state.fields_cache[self.get_cache_name()]
+
+
+class CheckFieldDefaultMixin:
+    _default_hint = ('<valid default>', '<invalid default>')
+
+    def _check_default(self):
+        if self.has_default() and self.default is not None and not callable(self.default):
+            return [
+                checks.Warning(
+                    "%s default should be a callable instead of an instance "
+                    "so that it's not shared between all field instances." % (
+                        self.__class__.__name__,
+                    ),
+                    hint=(
+                        'Use a callable instead, e.g., use `%s` instead of '
+                        '`%s`.' % self._default_hint
+                    ),
+                    obj=self,
+                    id='fields.E010',
+                )
+            ]
+        else:
+            return []
+
+    def check(self, **kwargs):
+        errors = super().check(**kwargs)
+        errors.extend(self._check_default())
+        return errors

docs/ref/checks.txt

@@ -140,6 +140,8 @@ Model fields
 * **fields.E008**: All ``validators`` must be callable.
 * **fields.E009**: ``max_length`` is too small to fit the longest value in
   ``choices`` (``<count>`` characters).
+* **fields.E010**: ``<field>`` default should be a callable instead of an
+  instance so that it's not shared between all field instances.
 * **fields.E100**: ``AutoField``\s must set primary_key=True.
 * **fields.E110**: ``BooleanField``\s do not accept null values. *This check
   appeared before support for null values was added in Django 2.1.*
@@ -747,7 +749,8 @@ fields:
 * **postgres.E001**: Base field for array has errors: ...
 * **postgres.E002**: Base field for array cannot be a related field.
 * **postgres.E003**: ``<field>`` default should be a callable instead of an
-  instance so that it's not shared between all field instances.
+  instance so that it's not shared between all field instances. *This check was
+  changed to* ``fields.E010`` *in Django 3.1*.
 
 ``sites``
 ---------

tests/postgres_tests/test_array.py

@@ -551,7 +551,7 @@ class TestChecks(PostgreSQLSimpleTestCase):
                 ),
                 hint='Use a callable instead, e.g., use `list` instead of `[]`.',
                 obj=MyModel._meta.get_field('field'),
-                id='postgres.E003',
+                id='fields.E010',
             )
         ])
 

tests/postgres_tests/test_hstore.py

@@ -231,7 +231,7 @@ class TestChecks(PostgreSQLSimpleTestCase):
                 ),
                 hint='Use a callable instead, e.g., use `dict` instead of `{}`.',
                 obj=MyModel._meta.get_field('field'),
-                id='postgres.E003',
+                id='fields.E010',
             )
         ])
 

tests/postgres_tests/test_json.py

@@ -429,7 +429,7 @@ class TestChecks(PostgreSQLSimpleTestCase):
                 ),
                 hint='Use a callable instead, e.g., use `dict` instead of `{}`.',
                 obj=MyModel._meta.get_field('field'),
-                id='postgres.E003',
+                id='fields.E010',
             )
         ])