RestKit 0.20 NSArray serialization problems

Question

I'm trying to serialize an NSArray of objects.

The object serializes as:

{"age":1,"name":"Foo"}

If I have an NSArray Containing these objects, it should serialize as:

[{"age":1,"name":"Bob"},{"age":4,"name":"Sally"},{"age":2,"name":"Jill"}]

However, when I serialize it directly via RestKit, I get the following:

{"age":[1,3,2],"name":["Sally","Jack","Bob"]}

When I inspect the RKMIMETypeSerialization, I see the following: (which would match the json output)

Parameters: {
    age =     (
        1,
        3,
        2
    );
    name =     (
        Sally,
        Jack,
        Bob
    );
}

I'm sure that I'm just doing something really silly, I have been playing with it can't figure it out.

Here is my mapping logic

+ (RKObjectMapping *)mapping {
    RKObjectMapping *mapping = [RKObjectMapping mappingForClass:[Item class]];
    [mapping addAttributeMappingsFromDictionary:@{
            @"name" : @"name",
            @"age" : @"age"
    }];

    return mapping;
}

And here is the logic doing the array serialization:

+ (NSString *)JSONStringFromArray:(NSArray *)array {
    RKObjectMapping *mapping = [Item mapping];
    RKRequestDescriptor *requestDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:mapping.inverseMapping objectClass:[Item class] rootKeyPath:nil];
    NSError *error;
    NSDictionary *parameters = [RKObjectParameterization parametersWithObject:array requestDescriptor:requestDescriptor error:&error];

// Serialize the object to JSON
    NSData *JSON = [RKMIMETypeSerialization dataFromObject:parameters MIMEType:RKMIMETypeJSON error:&error];

    NSString *jsonString = [[NSString alloc] initWithBytes:[JSON bytes]
                                                    length:[JSON length] encoding:NSUTF8StringEncoding];
    return jsonString;
}

Here are test classes: Item.h

#import <Foundation/Foundation.h>

@interface Item : NSObject
@property(nonatomic, strong) NSString *name;
@property(nonatomic) int age;

+ (void)testJsonSerialization;

+ (void)testJsonArraySerialization;

+ (Item *)itemWithName:(NSString *)string age:(int)age;
@end

Item.m

#import "Item.h"
#import <RestKit.h>

@implementation Item
+ (RKObjectMapping *)mapping {
    RKObjectMapping *mapping = [RKObjectMapping mappingForClass:[Item class]];
    [mapping addAttributeMappingsFromDictionary:@{
            @"name" : @"name",
            @"age" : @"age"
    }];

    return mapping;
}

- (NSString *)JSONString {
    RKObjectMapping *mapping = [Item mapping];
    RKRequestDescriptor *requestDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:mapping.inverseMapping objectClass:[Item class] rootKeyPath:nil];
    NSError *error;
    NSDictionary *parameters = [RKObjectParameterization parametersWithObject:self requestDescriptor:requestDescriptor error:&error];

// Serialize the object to JSON
    NSData *JSON = [RKMIMETypeSerialization dataFromObject:parameters MIMEType:RKMIMETypeJSON error:&error];

    NSString *jsonString = [[NSString alloc] initWithBytes:[JSON bytes]
                                                    length:[JSON length] encoding:NSUTF8StringEncoding];
    return jsonString;
}

+ (NSString *)JSONStringFromArray:(NSArray *)array {
    RKObjectMapping *mapping = [Item mapping];
    RKRequestDescriptor *requestDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:mapping.inverseMapping objectClass:[Item class] rootKeyPath:nil];
    NSError *error;
    NSDictionary *parameters = [RKObjectParameterization parametersWithObject:array requestDescriptor:requestDescriptor error:&error];

// Serialize the object to JSON
    NSData *JSON = [RKMIMETypeSerialization dataFromObject:parameters MIMEType:RKMIMETypeJSON error:&error];

    NSString *jsonString = [[NSString alloc] initWithBytes:[JSON bytes]
                                                    length:[JSON length] encoding:NSUTF8StringEncoding];
    return jsonString;
}

+ (void)testJsonSerialization {
    Item *item = [Item itemWithName:@"Foo" age:1];
    NSString *itemJSON = [item JSONString];
    NSLog(@"ItemJSON:\n%@\n\n", itemJSON);
}

+ (void)testJsonArraySerialization {
    NSArray *items = @[[Item itemWithName:@"Sally" age:1], [Item itemWithName:@"Jack" age:3], [Item itemWithName:@"Bob" age:2]];
    NSString *itemJSON = [Item JSONStringFromArray:items];
    NSLog(@"ItemArrayJSON:\n%@\n\n", itemJSON);
}

+ (Item *)itemWithName:(NSString *)name age:(int)age {
    Item *item = [[Item alloc] init];
    item.name = name;
    item.age = age;
    return item;
}
@end

To execute Have RestKit pod installed and then issue the following:

    [Item testJsonSerialization];
    [Item testJsonArraySerialization];

Note, maybe I'm not configuring the mapping correctly for the array serialization. Though this mapper works perfectly for deserializing the targeted json text up above.

Answer 1

RKObjectParameterization is expected to be used to serialise individual instances of the target of your object mapping and it statically serialises the instance into an NSMutableDictionary. You can't write a mapping to use with RKObjectParameterization that will serialise an array of objects to an array of dictionaries. You would need to do this yourself by looping over your array.