Expose whether a result was served from cache or fetched from the ser…

…ver (#176)

Closes #170.

Sources/Apollo/ApolloStore.swift

@@ -98,7 +98,7 @@ public final class ApolloStore {
 
       return try transaction.execute(selections: Query.Data.selections, onObjectWithKey: Query.rootCacheKey, variables: query.variables, accumulator: zip(mapper, dependencyTracker))
     }.map { (data: Query.Data, dependentKeys: Set<CacheKey>) in
-      GraphQLResult(data: data, errors: nil, dependentKeys: dependentKeys)
+      GraphQLResult(data: data, errors: nil, source:.cache, dependentKeys: dependentKeys)
     }
   }
 

Sources/Apollo/GraphQLResponse.swift

@@ -31,10 +31,10 @@ public final class GraphQLResponse<Operation: GraphQLOperation> {
       return firstly {
         try executor.execute(selections: Operation.Data.selections, on: dataEntry, withKey: Operation.rootCacheKey, variables: operation.variables, accumulator: zip(mapper, normalizer, dependencyTracker))
       }.map { (data, records, dependentKeys) in
-        (GraphQLResult(data: data, errors: errors, dependentKeys: dependentKeys), records)
+        (GraphQLResult(data: data, errors: errors, source: .server, dependentKeys: dependentKeys), records)
       }
     } else {
-      return Promise(fulfilled: (GraphQLResult(data: nil, errors: errors, dependentKeys: nil), nil))
+      return Promise(fulfilled: (GraphQLResult(data: nil, errors: errors, source: .server, dependentKeys: nil), nil))
     }
   }
 }

Sources/Apollo/GraphQLResult.swift

@@ -1,15 +1,24 @@
 /// Represents the result of a GraphQL operation.
 public struct GraphQLResult<Data> {
+    /// Represents source of data
+    public enum Source {
+        case cache
+        case server
+    }
+
   /// The typed result data, or `nil` if an error was encountered that prevented a valid response.
   public let data: Data?
   /// A list of errors, or `nil` if the operation completed without encountering any errors.
   public let errors: [GraphQLError]?
-
+  /// Source of data
+  public let source:Source
+
   let dependentKeys: Set<CacheKey>?
 
-  init(data: Data?, errors: [GraphQLError]?, dependentKeys: Set<CacheKey>?) {
+  init(data: Data?, errors: [GraphQLError]?, source:Source, dependentKeys: Set<CacheKey>?) {
     self.data = data
     self.errors = errors
-    self.dependentKeys = dependentKeys
+    self.dependentKeys = dependentKeys     
+    self.source = source
   }
 }