Refs #25415 -- Made MySQL backend skip field validation of unsupported models.

django/db/backends/mysql/validation.py

@@ -32,25 +32,33 @@ class DatabaseValidation(BaseDatabaseValidation):
         No character (varchar) fields can have a length exceeding 255
         characters if they have a unique index on them.
         """
-        from django.db import connection
-
         errors = super(DatabaseValidation, self).check_field(field, **kwargs)
 
         # Ignore any related fields.
-        if getattr(field, 'remote_field', None) is None:
+        if getattr(field, 'remote_field', None):
-            field_type = field.db_type(connection)
+            return errors
 
-            # Ignore any non-concrete fields
+        # Ignore fields with unsupported features.
-            if field_type is None:
+        db_supports_all_required_features = all(
-                return errors
+            getattr(self.connection.features, feature, False)
+            for feature in field.model._meta.required_db_features
+        )
+        if not db_supports_all_required_features:
+            return errors
 
-            if (field_type.startswith('varchar') and field.unique and
+        field_type = field.db_type(self.connection)
-                    (field.max_length is None or int(field.max_length) > 255)):
+
-                errors.append(
+        # Ignore non-concrete fields.
-                    checks.Error(
+        if field_type is None:
-                        'MySQL does not allow unique CharFields to have a max_length > 255.',
+            return errors
-                        obj=field,
+
-                        id='mysql.E001',
+        if (field_type.startswith('varchar') and field.unique and
-                    )
+                (field.max_length is None or int(field.max_length) > 255)):
+            errors.append(
+                checks.Error(
+                    'MySQL does not allow unique CharFields to have a max_length > 255.',
+                    obj=field,
+                    id='mysql.E001',
                 )
+            )
         return errors

tests/invalid_models_tests/test_ordinary_fields.py

@@ -217,7 +217,7 @@ class CharFieldTests(TestCase):
             field = models.CharField(unique=True, max_length=256)
 
         field = Model._meta.get_field('field')
-        validator = DatabaseValidation(connection=None)
+        validator = DatabaseValidation(connection=connection)
         errors = validator.check_field(field)
         expected = [
             Error(