Support batched queries (fix #1812)

docs/graphql/manual/api-reference/graphql-api/index.rst

@@ -28,9 +28,60 @@ The following types of requests can be made using the GraphQL API:
 - :doc:`Query / Subscription <query>`
 - :doc:`Mutation <mutation>`
 
+Batching operations
+-------------------
+
+The GraphQL API provides support for batched operations (which can be a combination of queries and mutations).
+The endpoint will accept an array of operations in place of a single operation, and return an array of corresponding 
+responses.
+
+**Example:** using a client which supports batching (such as Apollo Client), we can send two
+query operations in one request:
+
+.. graphiql::
+  :view_only:
+  :query:
+    query first {
+      author(where: {id: {_eq: 1}}) {
+        id
+        name
+      }
+    }
+    query second {
+      author(where: {id: {_eq: 2}}) {
+        id
+        name
+      }
+    }
+  :response:
+    [
+      {
+        "data": {
+          "author": [
+            {
+              "id": 1,
+              "name": "Justin"
+            }
+          ]
+        }
+      },
+      {
+        "data": {
+          "author": [
+            {
+              "id": 2,
+              "name": "Beltran"
+            }
+          ]
+        }
+      }
+    ]
+
+
 .. toctree::
   :maxdepth: 1
   :hidden:
 
   Query / Subscription <query>
   Mutation <mutation>
+  Batching operations <batching>

server/src-lib/Hasura/GraphQL/Transport/HTTP.hs

@@ -1,5 +1,6 @@
 module Hasura.GraphQL.Transport.HTTP
   ( runGQ
+  , runGQBatched
   ) where
 
 import qualified Network.HTTP.Types                     as N
@@ -24,7 +25,7 @@ runGQ
   => RequestId
   -> UserInfo
   -> [N.Header]
-  -> GQLReqUnparsed
+  -> GQLReq GQLQueryText
   -> m (HttpResponse EncJSON)
 runGQ reqId userInfo reqHdrs req = do
   E.ExecutionCtx _ sqlGenCtx pgExecCtx planCache sc scVer _ enableAL <- ask
@@ -36,6 +37,27 @@ runGQ reqId userInfo reqHdrs req = do
     E.GExPRemote rsi opDef  ->
       E.execRemoteGQ reqId userInfo reqHdrs req rsi opDef
 
+runGQBatched
+  :: ( MonadIO m
+     , MonadError QErr m
+     , MonadReader E.ExecutionCtx m
+     )
+  => RequestId
+  -> UserInfo
+  -> [N.Header]
+  -> GQLBatchedReqs GQLQueryText
+  -> m (HttpResponse EncJSON)
+runGQBatched reqId userInfo reqHdrs reqs =
+  case reqs of
+    GQLSingleRequest req ->
+      runGQ reqId userInfo reqHdrs req
+    GQLBatchedReqs batch -> do
+      -- It's unclear what we should do if we receive multiple
+      -- responses with distinct headers, so just do the simplest thing
+      -- in this case, and don't forward any.
+      let removeHeaders = flip HttpResponse Nothing . encJFromList . map _hrBody
+      removeHeaders <$> traverse (runGQ reqId userInfo reqHdrs) batch
+
 runHasuraGQ
   :: ( MonadIO m
      , MonadError QErr m

server/src-lib/Hasura/GraphQL/Transport/HTTP/Protocol.hs

@@ -1,5 +1,6 @@
 module Hasura.GraphQL.Transport.HTTP.Protocol
   ( GQLReq(..)
+  , GQLBatchedReqs(..)
   , GQLReqUnparsed
   , GQLReqParsed
   , toParsed
@@ -64,6 +65,24 @@ $(J.deriveJSON (J.aesonDrop 3 J.camelCase){J.omitNothingFields=True}
 
 instance (Hashable a) => Hashable (GQLReq a)
 
+-- | Batched queries are sent as a JSON array of
+-- 'GQLReq' records. This newtype exists to support
+-- the unusual JSON encoding.
+--
+-- See <https://github.com/hasura/graphql-engine/issues/1812>.
+data GQLBatchedReqs a
+  = GQLSingleRequest (GQLReq a)
+  | GQLBatchedReqs [GQLReq a]
+  deriving (Show, Eq, Generic)
+
+instance J.ToJSON a => J.ToJSON (GQLBatchedReqs a) where
+  toJSON (GQLSingleRequest q) = J.toJSON q
+  toJSON (GQLBatchedReqs qs) = J.toJSON qs
+
+instance J.FromJSON a => J.FromJSON (GQLBatchedReqs a) where
+  parseJSON arr@J.Array{} = GQLBatchedReqs <$> J.parseJSON arr
+  parseJSON other = GQLSingleRequest <$> J.parseJSON other
+
 newtype GQLQueryText
   = GQLQueryText
   { _unGQLQueryText :: Text

server/src-lib/Hasura/Server/App.hs

@@ -297,7 +297,7 @@ v1QueryHandler query = do
       instanceId <- scInstanceId . hcServerCtx <$> ask
       runQuery pgExecCtx instanceId userInfo schemaCache httpMgr sqlGenCtx (SystemDefined False) query
 
-v1Alpha1GQHandler :: (MonadIO m) => GH.GQLReqUnparsed -> Handler m (HttpResponse EncJSON)
+v1Alpha1GQHandler :: (MonadIO m) => GH.GQLBatchedReqs GH.GQLQueryText -> Handler m (HttpResponse EncJSON)
 v1Alpha1GQHandler query = do
   userInfo <- asks hcUser
   reqHeaders <- asks hcReqHeaders
@@ -312,11 +312,11 @@ v1Alpha1GQHandler query = do
   requestId <- asks hcRequestId
   let execCtx = E.ExecutionCtx logger sqlGenCtx pgExecCtx planCache
                 sc scVer manager enableAL
-  flip runReaderT execCtx $ GH.runGQ requestId userInfo reqHeaders query
+  flip runReaderT execCtx $ GH.runGQBatched requestId userInfo reqHeaders query
 
 v1GQHandler
   :: (MonadIO m)
-  => GH.GQLReqUnparsed
+  => GH.GQLBatchedReqs GH.GQLQueryText
   -> Handler m (HttpResponse EncJSON)
 v1GQHandler = v1Alpha1GQHandler
 

server/src-lib/Hasura/Server/Context.hs

@@ -17,4 +17,4 @@ data HttpResponse a
   = HttpResponse
   { _hrBody    :: !a
   , _hrHeaders :: !(Maybe Headers)
-  }
+  } deriving (Functor, Foldable, Traversable)

server/tests-py/queries/graphql_query/basic/select_query_batching.yaml

@@ -0,0 +1,25 @@
+description: GraphQL query to test batching in the style of Apollo
+url: /v1/graphql
+status: 200
+response:
+  - data:
+      user:
+      - id: '1'
+      - id: '2'
+  - data:
+      author:
+      - id: 1
+      - id: 2
+query:
+  - query: |
+      query {
+        user {
+          id
+        }
+      }
+  - query: |
+      query {
+        author {
+          id
+        }
+      }

server/tests-py/test_graphql_queries.py

@@ -60,6 +60,10 @@ def test_select_query_invalid_escape_sequence(self, hge_ctx, transport):
         transport = 'http'
         check_query_f(hge_ctx, self.dir() + "/select_query_invalid_escape_sequence.yaml", transport)
 
+    def test_select_query_batching(self, hge_ctx, transport):
+        transport = 'http'
+        check_query_f(hge_ctx, self.dir() + "/select_query_batching.yaml", transport)
+
     @classmethod
     def dir(cls):
         return 'queries/graphql_query/basic'

server/tests-py/validate.py

@@ -387,7 +387,8 @@ def go(result_node, selset):
 # Copy-pasta from: https://stackoverflow.com/q/12734517/176841 
 def stringify_keys(d):
  """Convert a dict's keys to strings if they are not."""
- for key in d.keys():
+ if isinstance(d, dict):
+   for key in d.keys():
      # check inner dict
      if isinstance(d[key], dict):
          value = stringify_keys(d[key])