mutation is also cached, with SplayTreeMap (#7)

Author: truongsinh

lib/src/core/query_manager.dart

@@ -119,11 +119,8 @@ class QueryManager {
       ).first;
 
       // save the data from fetchResult to the cache
-      if (
-          // should never cache a mutation
-          !(options is MutationOptions) &&
-              fetchResult.data != null &&
-              options.fetchPolicy != FetchPolicy.noCache) {
+      if (fetchResult.data != null &&
+          options.fetchPolicy != FetchPolicy.noCache) {
         cache.write(
           operation.toKey(),
           fetchResult.data,

lib/src/link/operation.dart

@@ -1,21 +1,36 @@
-import 'dart:convert';
+import 'dart:collection' show SplayTreeMap;
+import 'dart:convert' show json;
+import 'dart:io' show File;
 
 class Operation {
-  Operation({
+  factory Operation({
+    String document,
+    Map<String, dynamic> variables,
+    String operationName,
+    Map<String, dynamic> extensions,
+  }) =>
+      Operation._(
+        document: document,
+        variables: SplayTreeMap<String, dynamic>.of(variables),
+        operationName: operationName,
+        extensions: extensions,
+      );
+
+  Operation._({
     this.document,
     this.variables,
     this.operationName,
     this.extensions,
   });
 
   final String document;
-  final Map<String, dynamic> variables;
+  final SplayTreeMap<String, dynamic> variables;
   final String operationName;
   final Map<String, dynamic> extensions;
 
   final Map<String, dynamic> _context = <String, dynamic>{};
 
-  /// Sets the context of an opration by merging the new context with the old one.
+  /// Sets the context of an operation by merging the new context with the old one.
   void setContext(Map<String, dynamic> next) {
     _context.addAll(next);
   }
@@ -28,9 +43,14 @@ class Operation {
   }
 
   String toKey() {
-    /// XXX we're assuming here that variables will be serialized in the same order.
-    /// that might not always be true
-    final String encodedVariables = json.encode(variables);
+    /// SplayTreeMap is always sorted
+    final String encodedVariables =
+        json.encode(variables, toEncodable: (dynamic object) {
+      if (object is File) {
+        return object.path;
+      }
+      return object;
+    });
 
     return '$document|$encodedVariables|$operationName';
   }