Add check constraint support - needed a few Field changes

django/db/backends/__init__.py

@@ -435,6 +435,9 @@ class BaseDatabaseFeatures(object):
     # Does it support foreign keys?
     supports_foreign_keys = True
 
+    # Does it support CHECK constraints?
+    supports_check_constraints = True
+
     def __init__(self, connection):
         self.connection = connection
 

django/db/backends/creation.py

@@ -18,6 +18,7 @@ class BaseDatabaseCreation(object):
     destruction of test databases.
     """
     data_types = {}
+    data_type_check_constraints = {}
 
     def __init__(self, connection):
         self.connection = connection

django/db/backends/mysql/base.py

@@ -170,6 +170,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     requires_explicit_null_ordering_when_grouping = True
     allows_primary_key_0 = False
     uses_savepoints = True
+    supports_check_constraints = False
 
     def __init__(self, connection):
         super(DatabaseFeatures, self).__init__(connection)

django/db/backends/postgresql_psycopg2/creation.py

@@ -26,14 +26,19 @@ class DatabaseCreation(BaseDatabaseCreation):
         'GenericIPAddressField': 'inet',
         'NullBooleanField':  'boolean',
         'OneToOneField':     'integer',
-        'PositiveIntegerField': 'integer CHECK ("%(column)s" >= 0)',
-        'PositiveSmallIntegerField': 'smallint CHECK ("%(column)s" >= 0)',
+        'PositiveIntegerField': 'integer',
+        'PositiveSmallIntegerField': 'smallint',
         'SlugField':         'varchar(%(max_length)s)',
         'SmallIntegerField': 'smallint',
         'TextField':         'text',
         'TimeField':         'time',
     }
 
+    data_type_check_constraints = {
+        'PositiveIntegerField': '"%(column)s" >= 0',
+        'PositiveSmallIntegerField': '"%(column)s" >= 0',
+    }
+
     def sql_table_creation_suffix(self):
         assert self.connection.settings_dict['TEST_COLLATION'] is None, "PostgreSQL does not support collation setting at database creation time."
         if self.connection.settings_dict['TEST_CHARSET']:

django/db/backends/postgresql_psycopg2/introspection.py

@@ -137,7 +137,7 @@ def get_constraints(self, cursor, table_name):
                 kc.table_schema = %s AND
                 kc.table_name = %s
         """, ["public", table_name])
-        for constraint, column, kind in cursor.fetchall():
+        for constraint, column in cursor.fetchall():
             # If we're the first column, make the record
             if constraint not in constraints:
                 constraints[constraint] = {

django/db/backends/schema.py

@@ -19,9 +19,6 @@ class BaseDatabaseSchemaEditor(object):
     then the relevant actions, and then commit(). This is necessary to allow
     things like circular foreign key references - FKs will only be created once
     commit() is called.
-
-    TODO:
-        - Check constraints (PosIntField)
     """
 
     # Overrideable SQL templates
@@ -41,7 +38,7 @@ class BaseDatabaseSchemaEditor(object):
     sql_delete_column = "ALTER TABLE %(table)s DROP COLUMN %(column)s CASCADE"
     sql_rename_column = "ALTER TABLE %(table)s RENAME COLUMN %(old_column)s TO %(new_column)s"
 
-    sql_create_check = "ADD CONSTRAINT %(name)s CHECK (%(check)s)"
+    sql_create_check = "ALTER TABLE %(table)s ADD CONSTRAINT %(name)s CHECK (%(check)s)"
     sql_delete_check = "ALTER TABLE %(table)s DROP CONSTRAINT %(name)s"
 
     sql_create_unique = "ALTER TABLE %(table)s ADD CONSTRAINT %(name)s UNIQUE (%(columns)s)"
@@ -105,7 +102,8 @@ def column_sql(self, model, field, include_default=False):
         The field must already have had set_attributes_from_name called.
         """
         # Get the column's type and use that as the basis of the SQL
-        sql = field.db_type(connection=self.connection)
+        db_params = field.db_parameters(connection=self.connection)
+        sql = db_params['type']
         params = []
         # Check for fields that aren't actually columns (e.g. M2M)
         if sql is None:
@@ -169,6 +167,11 @@ def create_model(self, model, force=False):
             definition, extra_params = self.column_sql(model, field)
             if definition is None:
                 continue
+            # Check constraints can go on the column SQL here
+            db_params = field.db_parameters(connection=self.connection)
+            if db_params['check']:
+                definition += " CHECK (%s)" % db_params['check']
+            # Add the SQL to our big list
             column_sqls.append("%s %s" % (
                 self.quote_name(field.column),
                 definition,
@@ -295,6 +298,10 @@ def create_field(self, model, field, keep_default=False):
         # It might not actually have a column behind it
         if definition is None:
             return
+        # Check constraints can go on the column SQL here
+        db_params = field.db_parameters(connection=self.connection)
+        if db_params['check']:
+            definition += " CHECK (%s)" % db_params['check']
         # Build the SQL and run it
         sql = self.sql_create_column % {
             "table": self.quote_name(model._meta.db_table),
@@ -358,8 +365,10 @@ def alter_field(self, model, old_field, new_field, strict=False):
         If strict is true, raises errors if the old column does not match old_field precisely.
         """
         # Ensure this field is even column-based
-        old_type = old_field.db_type(connection=self.connection)
-        new_type = self._type_for_alter(new_field)
+        old_db_params = old_field.db_parameters(connection=self.connection)
+        old_type = old_db_params['type']
+        new_db_params = new_field.db_parameters(connection=self.connection)
+        new_type = new_db_params['type']
         if old_type is None and new_type is None and (old_field.rel.through and new_field.rel.through and old_field.rel.through._meta.auto_created and new_field.rel.through._meta.auto_created):
             return self._alter_many_to_many(model, old_field, new_field, strict)
         elif old_type is None or new_type is None:
@@ -417,6 +426,22 @@ def alter_field(self, model, old_field, new_field, strict=False):
                         "name": fk_name,
                     }
                 )
+        # Change check constraints?
+        if old_db_params['check'] != new_db_params['check'] and old_db_params['check']:
+            constraint_names = self._constraint_names(model, [old_field.column], check=True)
+            if strict and len(constraint_names) != 1:
+                raise ValueError("Found wrong number (%s) of check constraints for %s.%s" % (
+                    len(constraint_names),
+                    model._meta.db_table,
+                    old_field.column,
+                ))
+            for constraint_name in constraint_names:
+                self.execute(
+                    self.sql_delete_check % {
+                        "table": self.quote_name(model._meta.db_table),
+                        "name": constraint_name,
+                    }
+                )
         # Have they renamed the column?
         if old_field.column != new_field.column:
             self.execute(self.sql_rename_column % {
@@ -543,6 +568,16 @@ def alter_field(self, model, old_field, new_field, strict=False):
                     "to_column": self.quote_name(new_field.rel.get_related_field().column),
                 }
             )
+        # Does it have check constraints we need to add?
+        if old_db_params['check'] != new_db_params['check'] and new_db_params['check']:
+            self.execute(
+                self.sql_create_check % {
+                    "table": self.quote_name(model._meta.db_table),
+                    "name": self._create_index_name(model, [new_field.column], suffix="_check"),
+                    "column": self.quote_name(new_field.column),
+                    "check": new_db_params['check'],
+                }
+            )
 
     def _alter_many_to_many(self, model, old_field, new_field, strict):
         "Alters M2Ms to repoint their to= endpoints."
@@ -555,14 +590,6 @@ def _alter_many_to_many(self, model, old_field, new_field, strict):
             new_field.rel.through._meta.get_field_by_name(new_field.m2m_reverse_field_name())[0],
         )
 
-    def _type_for_alter(self, field):
-        """
-        Returns a field's type suitable for ALTER COLUMN.
-        By default it just returns field.db_type().
-        To be overriden by backend specific subclasses
-        """
-        return field.db_type(connection=self.connection)
-
     def _create_index_name(self, model, column_names, suffix=""):
         "Generates a unique name for an index/unique constraint."
         # If there is just one column in the index, use a default algorithm from Django
@@ -581,7 +608,7 @@ def _create_index_name(self, model, column_names, suffix=""):
             index_name = '%s%s' % (table_name[:(self.connection.features.max_index_name_length - len(part))], part)
         return index_name
 
-    def _constraint_names(self, model, column_names=None, unique=None, primary_key=None, index=None, foreign_key=None):
+    def _constraint_names(self, model, column_names=None, unique=None, primary_key=None, index=None, foreign_key=None, check=None):
         "Returns all constraint names matching the columns and conditions"
         column_names = set(column_names) if column_names else None
         constraints = self.connection.introspection.get_constraints(self.connection.cursor(), model._meta.db_table)
@@ -594,6 +621,8 @@ def _constraint_names(self, model, column_names=None, unique=None, primary_key=N
                     continue
                 if index is not None and infodict['index'] != index:
                     continue
+                if check is not None and infodict['check'] != check:
+                    continue
                 if foreign_key is not None and not infodict['foreign_key']:
                     continue
                 result.append(name)

django/db/backends/sqlite3/base.py

@@ -97,6 +97,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     has_bulk_insert = True
     can_combine_inserts_with_and_without_auto_increment_pk = False
     supports_foreign_keys = False
+    supports_check_constraints = False
 
     @cached_property
     def supports_stddev(self):

django/db/backends/sqlite3/schema.py

@@ -99,8 +99,10 @@ def delete_field(self, model, field):
 
     def alter_field(self, model, old_field, new_field, strict=False):
         # Ensure this field is even column-based
-        old_type = old_field.db_type(connection=self.connection)
-        new_type = self._type_for_alter(new_field)
+        old_db_params = old_field.db_parameters(connection=self.connection)
+        old_type = old_db_params['type']
+        new_db_params = new_field.db_parameters(connection=self.connection)
+        new_type = new_db_params['type']
         if old_type is None and new_type is None and (old_field.rel.through and new_field.rel.through and old_field.rel.through._meta.auto_created and new_field.rel.through._meta.auto_created):
             return self._alter_many_to_many(model, old_field, new_field, strict)
         elif old_type is None or new_type is None:

django/db/models/fields/__init__.py

@@ -232,12 +232,32 @@ def db_type(self, connection):
         # mapped to one of the built-in Django field types. In this case, you
         # can implement db_type() instead of get_internal_type() to specify
         # exactly which wacky database column type you want to use.
+        params = self.db_parameters(connection)
+        if params['type']:
+            if params['check']:
+                return "%s CHECK (%s)" % (params['type'], params['check'])
+            else:
+                return params['type']
+        return None
+
+    def db_parameters(self, connection):
+        """
+        Replacement for db_type, providing a range of different return
+        values (type, checks)
+        """
         data = DictWrapper(self.__dict__, connection.ops.quote_name, "qn_")
         try:
-            return (connection.creation.data_types[self.get_internal_type()]
-                    % data)
+            type_string = connection.creation.data_types[self.get_internal_type()] % data
         except KeyError:
-            return None
+            type_string = None
+        try:
+            check_string = connection.creation.data_type_check_constraints[self.get_internal_type()] % data
+        except KeyError:
+            check_string = None
+        return {
+            "type": type_string,
+            "check": check_string,
+        }
 
     @property
     def unique(self):

django/db/models/fields/related.py

@@ -1050,6 +1050,9 @@ def db_type(self, connection):
             return IntegerField().db_type(connection=connection)
         return rel_field.db_type(connection=connection)
 
+    def db_parameters(self, connection):
+        return {"type": self.db_type(connection), "check": []}
+
 class OneToOneField(ForeignKey):
     """
     A OneToOneField is essentially the same as a ForeignKey, with the exception
@@ -1292,3 +1295,6 @@ def db_type(self, connection):
         # A ManyToManyField is not represented by a single column,
         # so return None.
         return None
+
+    def db_parameters(self, connection):
+        return {"type": None, "check": None}

tests/modeltests/schema/models.py

@@ -7,6 +7,7 @@
 
 class Author(models.Model):
     name = models.CharField(max_length=255)
+    height = models.PositiveIntegerField(null=True, blank=True)
 
     class Meta:
         managed = False

tests/modeltests/schema/tests.py

@@ -347,6 +347,56 @@ def test_m2m_repoint(self):
             else:
                 self.fail("No FK constraint for tag_id found")
 
+    @skipUnless(connection.features.supports_check_constraints, "No check constraints")
+    def test_check_constraints(self):
+        """
+        Tests creating/deleting CHECK constraints
+        """
+        # Create the tables
+        editor = connection.schema_editor()
+        editor.start()
+        editor.create_model(Author)
+        editor.commit()
+        # Ensure the constraint exists
+        constraints = connection.introspection.get_constraints(connection.cursor(), Author._meta.db_table)
+        for name, details in constraints.items():
+            if details['columns'] == set(["height"]) and details['check']:
+                break
+        else:
+            self.fail("No check constraint for height found")
+        # Alter the column to remove it
+        new_field = IntegerField(null=True, blank=True)
+        new_field.set_attributes_from_name("height")
+        editor = connection.schema_editor()
+        editor.start()
+        editor.alter_field(
+            Author,
+            Author._meta.get_field_by_name("height")[0],
+            new_field,
+            strict = True,
+        )
+        editor.commit()
+        constraints = connection.introspection.get_constraints(connection.cursor(), Author._meta.db_table)
+        for name, details in constraints.items():
+            if details['columns'] == set(["height"]) and details['check']:
+                self.fail("Check constraint for height found")
+        # Alter the column to re-add it
+        editor = connection.schema_editor()
+        editor.start()
+        editor.alter_field(
+            Author,
+            new_field,
+            Author._meta.get_field_by_name("height")[0],
+            strict = True,
+        )
+        editor.commit()
+        constraints = connection.introspection.get_constraints(connection.cursor(), Author._meta.db_table)
+        for name, details in constraints.items():
+            if details['columns'] == set(["height"]) and details['check']:
+                break
+        else:
+            self.fail("No check constraint for height found")
+
     def test_unique(self):
         """
         Tests removing and adding unique constraints to a single column.