Change default cascade action to NO ACTION

persistent/Database/Persist/Quasi.hs

@@ -423,8 +423,9 @@ AnotherVeryLongTableName
 These options affects how a referring record behaves when the target record is changed.
 There are several options:
 
-* 'Restrict' - This is the default. It prevents the action from occurring.
-* 'Cascade' - this copies the change to the child record. If a parent record is deleted, then the child record will be deleted too.
+* 'NoAction' - This is the default since 2.15.0.0. It checks constraints at the end of the transaction, aborting it if a violation is found.
+* 'Restrict' - This is the default prior to 2.15.0.0. It immediately checks constraints, aborting the transaction if a violation is found.
+* 'Cascade' - This copies the change to the child record. If a parent record is deleted, then the child record will be deleted too.
 * 'SetNull' - If the parent record is modified, then this sets the reference to @NULL@. This only works on @Maybe@ foreign keys.
 * 'SetDefault' - This will set the column's value to the @default@ for the column, if specified.
 

persistent/Database/Persist/Sql/Internal.hs

@@ -167,12 +167,12 @@ mkColumns allDefs t overrides =
         $ ref (fieldDB fd) (fieldReference fd) (fieldAttrs fd)
 
     -- a 'Nothing' in the definition means that the QQ migration doesn't
-    -- specify behavior. the default is RESTRICT. setting this here
+    -- specify behavior. the default is NO ACTION. setting this here
     -- explicitly makes migrations run smoother.
     overrideNothings (FieldCascade { fcOnUpdate = upd, fcOnDelete = del }) =
         FieldCascade
-            { fcOnUpdate = upd <|> Just Restrict
-            , fcOnDelete = del <|> Just Restrict
+            { fcOnUpdate = upd <|> Just NoAction
+            , fcOnDelete = del <|> Just NoAction
             }
 
     ref :: FieldNameDB

persistent/Database/Persist/Types/Base.hs

@@ -555,7 +555,10 @@ data ForeignDef = ForeignDef
 -- This type is used in both parsing the model definitions and performing
 -- migrations. A 'Nothing' in either of the field values means that the
 -- user has not specified a 'CascadeAction'. An unspecified 'CascadeAction'
--- is defaulted to 'Restrict' when doing migrations.
+-- is defaulted to:
+--
+-- * 'NoAction' in versions @>=2.15.0.0@
+-- * 'Restrict' in versions @<2.15.0.0@
 --
 -- @since 2.11.0
 data FieldCascade = FieldCascade
@@ -585,7 +588,12 @@ renderFieldCascade (FieldCascade onUpdate onDelete) =
 -- change.
 --
 -- @since 2.11.0
-data CascadeAction = Cascade | Restrict | SetNull | SetDefault
+data CascadeAction
+    = Cascade
+    | NoAction -- ^ @since 2.15.0.0
+    | Restrict
+    | SetNull
+    | SetDefault
     deriving (Show, Eq, Read, Ord, Lift)
 
 -- | Render a 'CascadeAction' to 'Text' such that it can be used in a SQL
@@ -595,6 +603,7 @@ data CascadeAction = Cascade | Restrict | SetNull | SetDefault
 renderCascadeAction :: CascadeAction -> Text
 renderCascadeAction action = case action of
   Cascade    -> "CASCADE"
+  NoAction   -> "NO ACTION"
   Restrict   -> "RESTRICT"
   SetNull    -> "SET NULL"
   SetDefault -> "SET DEFAULT"