Add function keyE.

Give a value, keyE lifts the Key for that value into the query expression.

    keyE :: Esqueleto query expr backend =>
            Value (Key entity) -> expr (Value (Key entity))

src/Database/Esqueleto.hs

@@ -81,6 +81,7 @@ module Database.Esqueleto
 
     -- * Helpers
   , valkey
+  , keyE
 
     -- * Re-exports
     -- $reexports
@@ -376,6 +377,16 @@ valkey :: Esqueleto query expr backend =>
 valkey = val . Key . PersistInt64
 
 
+-- | Given a value, lift the Key for that value into the query expression.
+keyE :: Esqueleto query expr backend =>
+        Value (Key entity) -> expr (Value (Key entity))
+keyE v =
+  valkey $
+    case (unKey . unValue) v of
+      PersistInt64 x -> x
+      _ -> error "Esqueleto.keyE: Impossible!"
+
+
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