Dive into Objective-C runtime to flatten JSONModel

JSONModel is an iOS library, which allows rapid creation of smart data models. It can be used in iOS or OSX apps. JSONModel automatically introspects your model classes and the structure of your JSON input and reduces drastically the amount of code you have to write.

Upfront was the descripton from JSONModel Official Github page. In plain words (codes), if we have got such json input:

@{@“id”: @“123456”, @“name”: @“little”, @“model”: @{@“no”: @“model 1586”,  “desc”: @“a short description”}}

It can be directly mapped into the following class:

@interface Product : JSONModel
@property (copy, nonatomic) NSString *id;
@property (copy, nonatomic) NSString *name;
@property (copy, nonatomic) NSString *modelNo;
@property (copy, nonatomic) NSString *modelDesc;
@end

by overriding its keyMapper class function:

+(JSONKeyMapper*)keyMapper
{
    return [[JSONKeyMapper alloc] initWithDictionary:@{
    @“model.no”: @“modelNo”,
    @“model.desc”: @“modelDesc”
    }];
}

Specifying model.no rule in json format is mapped into modelNo property in the objc object. By setting these rule, we will get an Product object will its properties set to coresponding json inputs exactly.

However, by the time we have the reverse requirement, which is mapping modelNo key in json to model.no property in objc object, the JSONModel fails to do the mapping rule. That means, if we have such json input:

{@“id”: @“123456”, @“name”: @“little”, @“modelNo”: @“model 1586”,  @“modelDesc”: @“a short description”}

And the definition of JSONModel subclass:

@interface Model : JSONModel
@property (copy, nonatomic) NSString * no;
@property (copy, nonatomic) NSString * desc;
@end
@interface Product : JSONModel
@property (copy, nonatomic) NSString * id;
@property (copy, nonatomic) NSString * name;
@property (strong, nonatomic) Model * model;
@end

And overriding keyMapper:

+(JSONKeyMapper*)keyMapper
{
  return [[JSONKeyMapper alloc] initWithDictionary:@{
    @“modelNo”: @“model.no”,
    @“modelDesc”: @“model.desc”
  }];
}

We will not set the json values to our Product object as expected. How this can be done can be refered as my implementation.