Remove PUT restriction for all columns/single row

Fixes https://github.com/PostgREST/postgrest/issues/1452.

The single row restriction can be lifted because the
PUT will consider only the first object of the array.

src/PostgREST/ApiRequest.hs

@@ -191,11 +191,10 @@ userApiRequest confSchemas rootSpec req reqBody
       (CTOther "application/x-www-form-urlencoded", _) ->
         let json = M.fromList . map (toS *** JSON.String . toS) . parseSimpleQuery $ toS reqBody
             keys = S.fromList $ M.keys json in
-        Right $ ProcessedJSON (JSON.encode json) PJObject keys
+        Right $ ProcessedJSON (JSON.encode json) keys
       (ct, _) ->
         Left $ toS $ "Content-Type not acceptable: " <> toMime ct
-  rpcPrmsToJson = ProcessedJSON (JSON.encode $ M.fromList $ second JSON.toJSON <$> rpcQParams)
-                  PJObject (S.fromList $ fst <$> rpcQParams)
+  rpcPrmsToJson = ProcessedJSON (JSON.encode $ M.fromList $ second JSON.toJSON <$> rpcQParams) (S.fromList $ fst <$> rpcQParams)
   topLevelRange = fromMaybe allRange $ M.lookup "limit" ranges -- if no limit is specified, get all the request rows
   action =
     case method of
@@ -334,14 +333,14 @@ payloadAttributes raw json =
                 JSON.Object x -> S.fromList (M.keys x) == canonicalKeys
                 _ -> False) arr in
           if areKeysUniform
-            then Just $ ProcessedJSON raw (PJArray $ V.length arr) canonicalKeys
+            then Just $ ProcessedJSON raw canonicalKeys
             else Nothing
         Just _ -> Nothing
         Nothing -> Just emptyPJArray
 
-    JSON.Object o -> Just $ ProcessedJSON raw PJObject (S.fromList $ M.keys o)
+    JSON.Object o -> Just $ ProcessedJSON raw (S.fromList $ M.keys o)
 
     -- truncate everything else to an empty array.
     _ -> Just emptyPJArray
   where
-    emptyPJArray = ProcessedJSON (JSON.encode emptyArray) (PJArray 0) S.empty
+    emptyPJArray = ProcessedJSON (JSON.encode emptyArray) S.empty