Fix 1-to-many relationships serialization according to JSON API v1.0 specification

Author: RafaelKayumov

Classes/JSONAPIResourceParser.m

@@ -121,8 +121,8 @@ + (NSDictionary*)dictionaryFor:(NSObject <JSONAPIResource>*)resource {
                             [dictionaryArray addObject:[self link:valueElement from:resource withKey:[property jsonName]]];
                         }
 
-                        [linkage setValue:dictionaryArray forKey:[property jsonName]];
-                        
+                        NSDictionary *dataDictionary = @{@"data" : dictionaryArray};
+                        [linkage setValue:dataDictionary forKey:[property jsonName]];
                     } else {
                         NSFormatter *format = [property formatter];
 
@@ -366,10 +366,15 @@ + (NSDictionary*)link:(NSObject <JSONAPIResource>*)resource from:(NSObject <JSON
     }
 
     if (resource.ID) {
-        [reference setValue:@{
-                              @"type" : descriptor.type,
-                              @"id"   : resource.ID
-                              } forKey:@"data"];
+        NSDictionary *referenceObject = @{
+                                          @"type" : descriptor.type,
+                                          @"id"   : resource.ID
+                                          };
+        if ([[owner valueForKey:key] isKindOfClass:[NSArray class]]) {
+            reference = referenceObject.mutableCopy;
+        } else {
+            [reference setValue:referenceObject forKey:@"data"];
+        }
     }
 
     return reference;