Add inMany

Closes #404

Closes #602

src/Opaleye/Operators.hs

@@ -58,6 +58,7 @@ module Opaleye.Operators
  , sqlLength
  -- * Containment operators
  , in_
+ , inMany
  , inSelect
  -- * JSON operators
  , SqlIsJson
@@ -297,6 +298,19 @@ in_ fcas (Column a) = case NEL.nonEmpty (F.toList fcas) of
  Nothing -> T.sqlBool False
  Just xs -> Column $ HPQ.BinExpr HPQ.OpIn a (HPQ.ListExpr (fmap C.unColumn xs))
 
+-- | @inMany@ is a generalization of 'in_' to values with multiple
+-- fields. It is designed to be used in prefix form.
+--
+-- @inMany validUsers user@ checks whether @user@ is a valid user.
+-- @inMany validUsers@ is a function which checks whether a user is a
+-- valid user.
+inMany ::
+ (F.Foldable f, D.Default O.EqPP fields fields) =>
+ f fields ->
+ fields ->
+ F.Field T.SqlBool
+inMany xs x = ors (fmap (.=== x) xs)
+
 -- | True if the first argument occurs amongst the rows of the second,
 -- false otherwise.
 --