Stop writing data parsing code in your apps


Data parsing is one of most common tasks we need to do in our apps, yet still majority of people do this parsing by hand, always repeating the same code for each class they need to map.

I’ll show show you how you could simplify your code and make it more readable at the same time.

Usual parsing requires this steps:

  • make sure you translate NSNull to nil and not crash
  • gracefully handle optional params
  • do type conversions

Why Property Mapper?

There are libraries helping with that like Mantle, RESTKit and many more… But I wanted something that’s self contained, easy to change / remove and requires minimal amount of code.

I’ve created Property Mapper as part of working on Foldify, a simple self contained class that allows you to specify mapping between data you receive and data representation you have in your application. With some additional features.

I don’t like passing around JSON so I write parsing on top of native objects like NSDictionary/NSArray. If you get data as JSON just write a simple category that transforms JSON to native objects using NSJSONSerialization.

Example usage

Let’s assume you have object like this:

@interface KZPropertyTestObject : NSObject
@property(nonatomic, strong) NSURL *contentURL;
@property(nonatomic, strong) NSURL *videoURL;
@property(nonatomic, strong) NSNumber *type;
@property(nonatomic, strong) NSString *title;
@property(nonatomic, strong) NSString *uniqueID;

@end

and you receive data from server in this format:

@{
  @"videoURL" : @"http://test.com/video.mp4", 
	@"name" : @"Some Cool Video", 
	@"videoType" : [NSNull null], 
	@"sub_object" : @{
			@"title" : @616,
			@"arbitraryData" : @"data"
	}
}

this is the code you would write in your parsing code:

[KZPropertyMapper mapValuesFrom:dictionary toInstance:self usingMapping:@{
   @"videoURL" : @"@URL(contentURL)",
     @"name" : @"title",
     @"videoType" : @"type",
     @"sub_object" : @{
         @"title" : @"uniqueID"
     }
   }];

Quite obvious what it does but in case you are confused, it will translate videoURL string to contentURL NSURL object, it will also grab title from sub_object and assign it to uniqueID. It also handles NSNull.

Advanced usage

Let’s now change our mind and decide that we want our type property to be typedef enumeration, it’s quite easy with KZPropertyMapper, change type mapping to following and add following method:

@"videoType" : @"@Selector(videoTypeFromString:, type)",

//! implemented on instance you are parsing
- (NSUInteger)videoTypeFromString:(NSString *)type
{
  if ([type isEqualToString:@"shortVideo"]) {
    return VideoTypeShort;
  }

  return VideoTypeLong;
}

Done. Same approach will work for sub-object instances or anything that you can assign to property.

Referencing arrays items

If your data comes to you in ordered array instead of dictionaries you can reference that as well:

sourceData = @{@"sub_object_array" : @[@"test", @123]}

@{@"sub_object_array" : @{@1 : @"uniqueID"}

This will grab first item from sub_object_array and assign it to uniqueID. It also works recursively.

Expanding boxing capabilities

You can expand boxing capabilities across whole application easily, just add category on KZPropertyMapper that implements methods like this:

+ (id)boxValueAsType:(id)value
{
	//! your boxing
}

Now you can use @Type mapping everywhere in your code.

Conclusion

Unit tests should serve as documentation.

Github repo

Support my writing: PayPal Tip Jar or become a Patron