Stop repeating your data parsing code in iOS 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.

Usual parsing requires this steps:

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

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 solution that allows you to specify mapping between data you receive and data representation you have in your application... with some additional features, like type boxing, validation.

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 TestObject : 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" : KZBox(URL, contentURL),
     @"name" : KZProperty(title),
     @"videoType" : KZProperty(type),
     @"sub_object" : @{
         @"title" : KZProperty(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" : KZCall(videoTypeFromString:, type),

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

  return @(VideoTypeLong);
}

If you need property name being passed while using selectors, just pass two-argument selector in KZCall. Second argument will be property name passed as NSString.

@"video" : KZCall(objectFromDictionary:forPropertyName:, type),

//! implemented on instance you are parsing
- (id)objectFromDictionary:(NSDictionary *)dictionary forPropertyName:(NSString *)propertyName
{
  Class objectClass = [self classForProperty:propertyName];
  id object = [objectClass new];
  [object updateFromDictionary:dictionary];
  return object;
}

Done. KVC should also take care of escaping NSNumber into int if your property uses primitive type. Same approach will work for sub-object instances or anything that you can assign to property.

Validations

You can also validate your server data before mapping it:

[KZPropertyMapper mapValuesFrom:dictionary toInstance:self usingMapping:@{
    @"videoURL" : KZBox(URL, contentURL).isRequired().min(10),
    @"name" : KZProperty(title).lengthRange(5, 12),
    @"videoType" : KZProperty(type),
    @"sub_object" : @{
      @"title" : KZProperty(uniqueID),
    },
  }];

Validators can be chained together, you can specify as many as you wish for each field, validation happens on source data before mapping happens.

If validation fails mapValues will return NO as a result, and you can use expanded method to get list of validation errors.

Any validation errors will prevent mapping, as data might be corrupted and we don't want partially updated data.

Built-in validations

Strings

• isRequired
• matchesRegEx
• length
• minLength
• maxLength
• lengthRange
• oneOf
• equalTo

Numbers

• min
• max
• range

If you want more you can add validations as categories on KZPropertyDescriptor, check sample code to see how it's done, it's extremely simple.

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 : KZProperty(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.

Changelog

2.5.0

• Added KZList that allows you to map single source property into multiple target ones.
• Added type checking while parsing, if mismatched type is found a property will be ignored and a warning will be generated.
• Fixed few minor bugs when working with unexpected server responses.

@{
  	@"videoURL" : KZList(
				KZBoxT(object, URL, contentURL),
				KZPropertyT(object, uniqueID),
				KZCallT(object, passthroughMethod:, type)
			)
}

Contributed by Marek Cirkos

2.0

• New property syntax (old one still works) that allows you to get compile errors when you misspell property names.
• Introduced concept of validators, chain-able.

Time to implement this changes was sponsored by The App Business.

Installing

• Using CocoaPods: Add the following line to your Podfile:

  pod "KZPropertyMapper"

• Using Carthage: Add the following to your Cartfile:

  github "krzysztofzablocki/KZPropertyMapper" "master"

• Or just add the KZPropertyMapper/ folder to your project, making sure you enable ARC on these files.

Final note

Unit tests should serve as documentation. Default boxing types include @URL and @Date.

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