Fixed #18757, #14462, #21565 -- Reworked database-python type conversions

Complete rework of translating data values from database

Deprecation of SubfieldBase, removal of resolve_columns and
convert_values in favour of a more general converter based approach and
public API Field.from_db_value(). Now works seamlessly with aggregation,
.values() and raw queries.

Thanks to akaariai in particular for extensive advice and inspiration,
also to shaib, manfre and timograham for their reviews.

1 files changed, 6 insertions, 1 deletions

diff --git a/tests/custom_pk/fields.py b/tests/custom_pk/fields.py
index 2aa3bad963..1f3265952a 100644
--- a/tests/custom_pk/fields.py
+++ b/tests/custom_pk/fields.py
@@ -23,7 +23,7 @@ class MyWrapper(object):
         return self.value == other
 
 
-class MyAutoField(six.with_metaclass(models.SubfieldBase, models.CharField)):
+class MyAutoField(models.CharField):
 
     def __init__(self, *args, **kwargs):
         kwargs['max_length'] = 10
@@ -43,6 +43,11 @@ class MyAutoField(six.with_metaclass(models.SubfieldBase, models.CharField)):
             value = MyWrapper(value)
         return value
 
+    def from_db_value(self, value, connection):
+        if not value:
+            return
+        return MyWrapper(value)
+
     def get_db_prep_save(self, value, connection):
         if not value:
             return