New SqlEntity constraint synonym.

src/Database/Esqueleto.hs

@@ -38,6 +38,7 @@ module Database.Esqueleto
     -- * SQL backend
   , SqlQuery
   , SqlExpr
+  , SqlEntity
   , select
   , selectDistinct
   , selectSource

src/Database/Esqueleto/Internal/Sql.hs

@@ -14,6 +14,7 @@ module Database.Esqueleto.Internal.Sql
   ( -- * The pretty face
     SqlQuery
   , SqlExpr
+  , SqlEntity
   , select
   , selectSource
   , selectDistinct
@@ -74,6 +75,11 @@ instance Applicative SqlQuery where
   (<*>) = ap
 
 
+-- | Constraint synonym for @persistent@ entities whose backend
+-- is 'SqlPersist'.
+type SqlEntity ent = (PersistEntity ent, PersistEntityBackend ent ~ SqlPersist)
+
+
 ----------------------------------------------------------------------
 
 
@@ -498,8 +504,7 @@ delete = rawExecute DELETE
 -- @
 update :: ( MonadLogger m
           , MonadResourceBase m
-          , PersistEntity val
+          , SqlEntity val )
-          , PersistEntityBackend val ~ SqlPersist )
        => (SqlExpr (Entity val) -> SqlQuery ())
        -> SqlPersist m ()
 update = rawExecute UPDATE . from