Add docs and improve merging of records from WebSockets into cache. (#…

…1892)

* Add docs and improve merging of records from WebSockets into cache.

* Fix compiler bug issue

Sources/Apollo/ApolloStore.swift

@@ -64,6 +64,13 @@ public final class ApolloStore {
     }
   }
 
+  /// Merges a `RecordSet` into the normalized cache.
+  /// - Parameters:
+  ///   - records: The records to be merged into the cache.
+  ///   - identifier: [optional] A unique identifier for the request that kicked off this change,
+  ///                 to assist in de-duping cache hits for watchers.
+  ///   - callbackQueue: The queue to call the completion block on. Defaults to `DispatchQueue.main`.
+  ///   - completion: [optional] A completion block to be called after records are merged into the cache.
   public func publish(records: RecordSet, identifier: UUID? = nil, callbackQueue: DispatchQueue = .main, completion: ((Result<Void, Error>) -> Void)? = nil) {
     queue.async(flags: .barrier) {
       do {

Sources/Apollo/GraphQLResponse.swift

@@ -19,6 +19,11 @@ public final class GraphQLResponse<Data: GraphQLSelectionSet> {
     self.variables = operation.variables
   }
 
+  /// Parses a response into a `GraphQLResult` and a `RecordSet`.
+  /// The result can be sent to a completion block for a request.
+  /// The `RecordSet` can be merged into a local cache.
+  /// - Parameter cacheKeyForObject: See `CacheKeyForObject`
+  /// - Returns: A `GraphQLResult` and a `RecordSet`.
   public func parseResult(cacheKeyForObject: CacheKeyForObject? = nil) throws -> (GraphQLResult<Data>, RecordSet?) {
     let errors: [GraphQLError]?
 

Sources/ApolloWebSocket/WebSocketTransport.swift

@@ -79,6 +79,7 @@ public class WebSocketTransport {
   ///
   /// - Parameters:
   ///   - websocket: The websocket client to use for creating a websocket connection.
+  ///   - store: [optional] The `ApolloStore` used as a local cache. Defaults to `nil`.
   ///   - clientName: The client name to use for this client. Defaults to `Self.defaultClientName`
   ///   - clientVersion: The client version to use for this client. Defaults to `Self.defaultClientVersion`.
   ///   - sendOperationIdentifiers: Whether or not to send operation identifiers with operations. Defaults to false.
@@ -362,24 +363,36 @@ extension WebSocketTransport: NetworkTransport {
       return EmptyCancellable()
     }
 
-    return WebSocketTask(self, operation) { [store] result in
+    return WebSocketTask(self, operation) { [weak store, contextIdentifier, callbackQueue] result in
       switch result {
       case .success(let jsonBody):
-        let response = GraphQLResponse(operation: operation, body: jsonBody)
-        if let store = store {
-          do {
-            let (_, records) = try response.parseResult(cacheKeyForObject: store.cacheKeyForObject)
-            if let records = records {
-              store.publish(records: records, identifier: nil)
+        do {
+          let response = GraphQLResponse(operation: operation, body: jsonBody)
+
+          if let store = store {
+            let (graphQLResult, parsedRecords) = try response.parseResult(cacheKeyForObject: store.cacheKeyForObject)
+            guard let records = parsedRecords else {
+              callCompletion(with: .success(graphQLResult))
+              return
+            }
+
+            store.publish(records: records,
+                          identifier: contextIdentifier,
+                          callbackQueue: callbackQueue) { result in
+              switch result {
+              case .success:
+                completionHandler(.success(graphQLResult))
+
+              case let .failure(error):
+                callCompletion(with: .failure(error))
+              }
             }
-          } catch {
-            callCompletion(with: .failure(error))
+
+          } else {
+            let graphQLResult = try response.parseResultFast()
+            callCompletion(with: .success(graphQLResult))
           }
-        }
-
-        do {
-          let graphQLResult = try response.parseResultFast()
-          callCompletion(with: .success(graphQLResult))
+
         } catch {
           callCompletion(with: .failure(error))
         }