How to map this JSON array to objects in RestKit 2

Question

I have a JSON structure like this:

[
    {
        "id" : "1",
        "name" : "Group 1"
    },
    {
        "id" : "2",
        "name" : "Group 2"
    },
    {
        "id" : "3",
        "name" : "Group 3"
    }
]

Please pay attention it begins with [ and ends with ]. How to map this-like JSON to array of Group objects using RestKit 2?

I tried with classic:

RKObjectMapping* groupMapping = [RKObjectMapping mappingForClass:[Group class]];
[groupMapping addAttributeMappingsFromDictionary:@{
        @"id" : @"groupID",
        @"name" : @"name"
}];
return groupMapping;

Then I'm using RKMappingTest to verify mapping, but I'm usually getting error:

restkit.object_mapping:RKMappingOperation.m:440 Failed transformation of value at keyPath 'id' to representation of type 'NSString': Error Domain=org.restkit.RKValueTransformers.ErrorDomain Code=3002 "Failed transformation of value...

After parsing of JSON with:

_parsedJSON = [RKTestFixture parsedObjectWithContentsOfFixture:@"groups.json"];

_parsedJSON is an array of dictionaries.

Does it work for real but not during test? I don't recall if there is a limitation with conversion of NSString to NSNumber... — Wain
– Wain, Commented Dec 18, 2013 at 15:48
The problem is not conversion of NSString to NSNumber, but with the JSON structure. If a JSON would be in format like {"":[ <array of objects> ]} (pay attention at enclosing brackets{}), everything goes well. — mixtly87
– mixtly87, Commented Dec 18, 2013 at 18:15

Wain · Accepted Answer · 2013-12-18 18:24:03Z

1

Failed transformation of value at keyPath 'id'

This is because it can't convert an array to a string.

The type of test your using cannot handle this JSON because it isn't a single mapping, it's multiple mappings, and the multiplicity is not handled by the mapping class.

When the mapping runs, it calls valueForKey: on an array and gets an array back. It expects to be calling on a dictionary and getting a string (or number).

So, basically, only test mapping individual objects.

answered Dec 18, 2013 at 18:24

Wain

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3 Comments

mixtly87 Over a year ago

But is there any way I can map this JSON to an array of objects? This is what I get from REST server and I can't change it. I am willing to try altering JSON just before mapping starts. Is there a hook in RestKit 2 where I can change the parsed JSON (ie, create a Dictionary which will hold an array)? Then I could map successfully.

Wain Over a year ago

We're talking about a test - make it appropriate. Mapping tests should only check the mapping itself. And that is a singular thing. It's possible that if you set destinationObject to a mutable array then RestKit might infer what you want, not sure on that though.

mixtly87 Over a year ago

It won't map to array in that case. But I decided to test single object mapping, not an array of objects, since that works automatically then.

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