Fixed #25143 -- Added ArrayField.from_db_value().

Thanks Karan Lyons for contributing to the patch.

django/contrib/postgres/fields/array.py

@@ -28,6 +28,10 @@ class ArrayField(Field):
         if self.size:
             self.default_validators = self.default_validators[:]
             self.default_validators.append(ArrayMaxLengthValidator(self.size))
+        # For performance, only add a from_db_value() method if the base field
+        # implements it.
+        if hasattr(self.base_field, 'from_db_value'):
+            self.from_db_value = self._from_db_value
         super(ArrayField, self).__init__(**kwargs)
 
     @property
@@ -100,6 +104,14 @@ class ArrayField(Field):
             value = [self.base_field.to_python(val) for val in vals]
         return value
 
+    def _from_db_value(self, value, expression, connection, context):
+        if value is None:
+            return value
+        return [
+            self.base_field.from_db_value(item, expression, connection, context)
+            for item in value
+        ]
+
     def value_to_string(self, obj):
         values = []
         vals = self.value_from_object(obj)

tests/postgres_tests/migrations/0002_create_test_models.py

@@ -4,6 +4,7 @@ from __future__ import unicode_literals
 from django.db import migrations, models
 
 from ..fields import *  # NOQA
+from ..models import TagField
 
 
 class Migration(migrations.Migration):
@@ -55,6 +56,7 @@ class Migration(migrations.Migration):
                 ('ips', ArrayField(models.GenericIPAddressField(), size=None)),
                 ('uuids', ArrayField(models.UUIDField(), size=None)),
                 ('decimals', ArrayField(models.DecimalField(max_digits=5, decimal_places=2), size=None)),
+                ('tags', ArrayField(TagField(), blank=True, null=True, size=None)),
             ],
             options={
                 'required_db_vendor': 'postgresql',

tests/postgres_tests/models.py

@@ -6,6 +6,35 @@ from .fields import (
 )
 
 
+class Tag(object):
+    def __init__(self, tag_id):
+        self.tag_id = tag_id
+
+    def __eq__(self, other):
+        return isinstance(other, Tag) and self.tag_id == other.tag_id
+
+
+class TagField(models.SmallIntegerField):
+
+    def from_db_value(self, value, expression, connection, context):
+        if value is None:
+            return value
+        return Tag(int(value))
+
+    def to_python(self, value):
+        if isinstance(value, Tag):
+            return value
+        if value is None:
+            return value
+        return Tag(int(value))
+
+    def get_prep_value(self, value):
+        return value.tag_id
+
+    def get_db_prep_value(self, value, connection, prepared=False):
+        return self.get_prep_value(value)
+
+
 class PostgreSQLModel(models.Model):
     class Meta:
         abstract = True
@@ -38,6 +67,7 @@ class OtherTypesArrayModel(PostgreSQLModel):
     ips = ArrayField(models.GenericIPAddressField())
     uuids = ArrayField(models.UUIDField())
     decimals = ArrayField(models.DecimalField(max_digits=5, decimal_places=2))
+    tags = ArrayField(TagField(), blank=True, null=True)
 
 
 class HStoreModel(PostgreSQLModel):

tests/postgres_tests/test_array.py

@@ -15,7 +15,7 @@ from . import PostgreSQLTestCase
 from .models import (
     ArrayFieldSubclass, CharArrayModel, DateTimeArrayModel, IntegerArrayModel,
     NestedIntegerArrayModel, NullableIntegerArrayModel, OtherTypesArrayModel,
-    PostgreSQLModel,
+    PostgreSQLModel, Tag,
 )
 
 try:
@@ -92,12 +92,24 @@ class TestSaveLoad(PostgreSQLTestCase):
             ips=['192.168.0.1', '::1'],
             uuids=[uuid.uuid4()],
             decimals=[decimal.Decimal(1.25), 1.75],
+            tags=[Tag(1), Tag(2), Tag(3)],
         )
         instance.save()
         loaded = OtherTypesArrayModel.objects.get()
         self.assertEqual(instance.ips, loaded.ips)
         self.assertEqual(instance.uuids, loaded.uuids)
         self.assertEqual(instance.decimals, loaded.decimals)
+        self.assertEqual(instance.tags, loaded.tags)
+
+    def test_null_from_db_value_handling(self):
+        instance = OtherTypesArrayModel.objects.create(
+            ips=['192.168.0.1', '::1'],
+            uuids=[uuid.uuid4()],
+            decimals=[decimal.Decimal(1.25), 1.75],
+            tags=None,
+        )
+        instance.refresh_from_db()
+        self.assertIsNone(instance.tags)
 
     def test_model_set_on_base_field(self):
         instance = IntegerArrayModel()
@@ -306,11 +318,13 @@ class TestOtherTypesExactQuerying(PostgreSQLTestCase):
         self.ips = ['192.168.0.1', '::1']
         self.uuids = [uuid.uuid4()]
         self.decimals = [decimal.Decimal(1.25), 1.75]
+        self.tags = [Tag(1), Tag(2), Tag(3)]
         self.objs = [
             OtherTypesArrayModel.objects.create(
                 ips=self.ips,
                 uuids=self.uuids,
                 decimals=self.decimals,
+                tags=self.tags,
             )
         ]
 
@@ -332,6 +346,12 @@ class TestOtherTypesExactQuerying(PostgreSQLTestCase):
             self.objs
         )
 
+    def test_exact_tags(self):
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(tags=self.tags),
+            self.objs
+        )
+
 
 @isolate_apps('postgres_tests')
 class TestChecks(PostgreSQLTestCase):