Fixed #29517 -- Added support for SQLite column check constraints on positive integer fields.

django/db/backends/sqlite3/base.py

@@ -76,6 +76,10 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         'TimeField': 'time',
         'UUIDField': 'char(32)',
     }
+    data_type_check_constraints = {
+        'PositiveIntegerField': '"%(column)s" >= 0',
+        'PositiveSmallIntegerField': '"%(column)s" >= 0',
+    }
     data_types_suffix = {
         'AutoField': 'AUTOINCREMENT',
         'BigAutoField': 'AUTOINCREMENT',

django/db/backends/sqlite3/features.py

@@ -14,7 +14,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_timezones = False
     max_query_params = 999
     supports_mixed_date_datetime_comparisons = False
-    supports_column_check_constraints = False
     autocommits_when_autocommit_is_off = True
     can_introspect_decimal_field = False
     can_introspect_positive_integer_field = True

django/db/backends/sqlite3/introspection.py

@@ -231,6 +231,32 @@ class DatabaseIntrospection(BaseDatabaseIntrospection):
         one or more columns.
         """
         constraints = {}
+        # Find inline check constraints.
+        try:
+            table_schema = cursor.execute(
+                "SELECT sql FROM sqlite_master WHERE type='table' and name=%s" % (
+                    self.connection.ops.quote_name(table_name),
+                )
+            ).fetchone()[0]
+        except TypeError:
+            # table_name is a view.
+            pass
+        else:
+            fields_with_check_constraints = [
+                schema_row.strip().split(' ')[0][1:-1]
+                for schema_row in table_schema.split(',')
+                if schema_row.find('CHECK') >= 0
+            ]
+            for field_name in fields_with_check_constraints:
+                # An arbitrary made up name.
+                constraints['__check__%s' % field_name] = {
+                    'columns': [field_name],
+                    'primary_key': False,
+                    'unique': False,
+                    'foreign_key': False,
+                    'check': True,
+                    'index': False,
+                }
         # Get the index info
         cursor.execute("PRAGMA index_list(%s)" % self.connection.ops.quote_name(table_name))
         for row in cursor.fetchall():

docs/releases/2.2.txt

@@ -218,7 +218,10 @@ Database backend API
 Miscellaneous
 -------------
 
-* ...
+* On SQLite, ``PositiveIntegerField`` and ``PositiveSmallIntegerField`` now
+  include a check constraint to prevent negative values in the database. If you
+  have existing invalid data and run a migration that recreates a table, you'll
+  see ``CHECK constraint failed``.
 
 .. _deprecated-features-2.2: