Serialize and Deserialize Objective-C objects into JSON

Question

I need to serialize and deserialize objective-c objects into JSON to store in CouchDB. Do people have any example code for best practice for a general solution? I looked at a few JSON framework and they are stopped at the NSDictionary/NSArray level. i.e. A lot of framework will serialize and deserialize NSDictionary/NSArray into JSON. But I still have to do the work to convert NSDictionary into Objective-C objects.

To make things more complex, my Object A can have reference to an NSArray/NSDictionary of Object Bs.

My question is very similar to this question with addition of the collection requirement.

Instantiating Custom Class from NSDictionary

Solution 1

It sounds like you're looking for a serialization library that can let you convert objects of your own custom classes into JSON, and then reconstitute them back. Serialization of property-list types (NSArray, NSNumber, etc.) already exists in 3rd party libraries, and is even built into OS X 10.7 and iOS 5.

So, I think the answer is basically "no". I asked this exact question a month or two ago on the cocoa-dev mailing list, and the closest I got to a hit was from Mike Abdullah, pointing to an experimental library he'd written:

https://github.com/mikeabdullah/KSPropertyListEncoder

This archives objects to in-memory property lists, but as I said there are already APIs for converting those into JSON.

There's also a commercial app called Objectify that claims to be able to do something similar:

http://tigerbears.com/objectify/

It's possible I'll end up implementing what you're asking for as part of my CouchCocoa library, but I haven't dived into that task yet.

https://github.com/couchbaselabs/CouchCocoa

Solution 2

Finally we can solve this problem easily using JSONModel. This is the best method so far. JSONModel is a library that generically serialize/deserialize your object based on Class. You can even use non-nsobject based for property like int, short and float. It can also cater nested-complex JSON.

Considering this JSON example:

{ "accounting" : [{ "firstName" : "John",  
                    "lastName"  : "Doe",
                    "age"       : 23 },

                  { "firstName" : "Mary",  
                    "lastName"  : "Smith",
                    "age"       : 32 }
                              ],                            
  "sales"      : [{ "firstName" : "Sally", 
                    "lastName"  : "Green",
                    "age"       : 27 },

                  { "firstName" : "Jim",   
                    "lastName"  : "Galley",
                    "age"       : 41 }
                  ]}

1) Deserialize example. in header file:

#import "JSONModel.h"

@interface Person : JSONModel 
@property (nonatomic, strong) NSString *firstName;
@property (nonatomic, strong) NSString *lastName;
@property (nonatomic, strong) NSNumber *age;
@end

@protocol Person;

@interface Department : JSONModel
@property (nonatomic, strong) NSMutableArray<Person> *accounting;
@property (nonatomic, strong) NSMutableArray<Person> *sales;
@end

in implementation file:

#import "JSONModelLib.h"
#import "myJSONClass.h"

NSString *responseJSON = /*from example*/;
Department *department = [[Department alloc] initWithString:responseJSON error:&err];
if (!err)
{
    for (Person *person in department.accounting) {

        NSLog(@"%@", person.firstName);
        NSLog(@"%@", person.lastName);
        NSLog(@"%@", person.age);         
    }

    for (Person *person in department.sales) {

        NSLog(@"%@", person.firstName);
        NSLog(@"%@", person.lastName);
        NSLog(@"%@", person.age);         
    }
}

2) Serialize Example. In implementation file:

#import "JSONModelLib.h"
#import "myJSONClass.h"

Department *department = [[Department alloc] init];

Person *personAcc1 = [[Person alloc] init];
personAcc1.firstName = @"Uee";
personAcc1.lastName = @"Bae";
personAcc1.age = [NSNumber numberWithInt:22];
[department.accounting addOject:personAcc1];

Person *personSales1 = [[Person alloc] init];
personSales1.firstName = @"Sara";
personSales1.lastName = @"Jung";
personSales1.age = [NSNumber numberWithInt:20];
[department.sales addOject:personSales1];

NSLog(@"%@", [department toJSONString]);

And this is NSLog result from Serialize example:

{ "accounting" : [{ "firstName" : "Uee",  
                    "lastName"  : "Bae",
                    "age"       : 22 }
                 ],                            
  "sales"      : [{ "firstName" : "Sara", 
                    "lastName"  : "Jung",
                    "age"       : 20 }
                  ]}

Solution 3

You can easily add JSON capability to NSObject class with the help of NSDictionary,NSArray and NSJSONSerialization

Serialization:

Just see the example it will be very easy to understand.

Adding JSON Capability to NSObject Class:-

@interface JsonClassEmp : NSObject

@property(strong,nonatomic)NSString *EmpName,*EmpCode;

-(NSDictionary*)GetJsonDict;

@end

@implementation JsonClassEmp

@synthesize EmpName,EmpCode;

//Add all the properties of the class in it.
-(NSDictionary*)GetJsonDict
{
    return [NSDictionary dictionaryWithObjectsAndKeys:EmpName,@"EmpName",EmpCode,@"EmpCode", nil];
}

@end

JSON String Generator:-

In iOS 5, Apple introduced NSJSONSerialization, for parsing JSON strings so by using that we will generate JSON string.

-(NSString*)GetJSON:(id)object
{
    NSError *writeError = nil;

    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:object options:NSJSONWritingPrettyPrinted error:&writeError];

    NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];

    return jsonString;
}

Moving towards Apple’s implementation is always safer to use since you have the guarantee that it will be maintained and kept up to date.

Way to use:-

- (void)viewDidLoad
{
    [super viewDidLoad];

    JsonClassEmp *emp1=[[JsonClassEmp alloc]init];

    [emp1 setEmpName:@"Name1"];

    [emp1 setEmpCode:@"1"];

    JsonClassEmp *emp2=[[JsonClassEmp alloc]init];

    [emp2 setEmpName:@"Name2"];

    [emp2 setEmpCode:@"2"];

    //Add the NSDictionaries of the instances in NSArray
    NSArray *arrEmps_Json=@[emp1.GetJsonDict,emp2.GetJsonDict];

    NSLog(@"JSON Output: %@", [self GetJSON:arrEmps_Json]);

}

Reference

Deserialization:

It's usual way of getting the deserialized data into NSDictionary or NSArray then assign it to class properties.

I am sure using the methods and ideas used above you can serialize & deserialize complex json easily.

Solution 4

You may want to try JTObjectMapping. Their description:

JTObjectMapping - Inspired by RestKit. A very simple objective-c framework that maps a JSON response from NSDictionary or NSArray to NSObject subclasses for iOS.

It's very small (unlike RestKit) and works great.

Solution 5

This is possible using the RestKit library's object mapping system.

http://restkit.org/

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