Restkit Dynamic Mapping for optional attribute

Question

I am getting a json document like this from a ws:

{
   ...
   error=true,
   errorMsg="xyz",
   errorCode="1234"
}

But these attributes are optional so sometimes they are present and sometime they are not.

I added a dynamic mapping for reading only error - only if error is set to true

either:

[dynamicMapping addMatcher:[RKObjectMappingMatcher matcherWithKeyPath:@"error" expectedValue:[NSNumber numberWithInt:1] objectMapping:errorMapping]];

or

[dynamicMapping setObjectMappingForRepresentationBlock:^RKObjectMapping *(id representation) {
        if ([[representation valueForKey:@"error"] isEqualToNumber:[NSNumber numberWithInt:1]]) {
            return errorMapping;
        } 

        return nil;
    }];

Everything is working fine if error=true but if the error attributes are missing I get a warning:

restkit.object_mapping:RKMapperOperation.m:98 Adding mapping error: Could not find an object mapping for keyPath: '<null>'

I just want to get rid of the warning. What is the best practice for this problem? How do I mark the attribute as optional?

Hi, yes I use the same mapping ("errorMapping") for server errors with status code RKStatusCodeClassServerError = 500. So if an error occurs on the server the server send the error msg in a json format. — cloudnaut
I mean how is your success scenario handled? Usually your dynamic mapping would check the status and then either return the error mapping or the success mapping. — Wain
A success would be if either error=false or no error attributes are specified. Error=false with a message would be a warning for which I may also add an object and add another dynamic mapping. — cloudnaut

Wain Wain · Accepted Answer · 2013-07-09T13:32:58

To remove the warning, you need to complete your mapping configuration, because currently you're only giving it information for half of the scenarios. The warning is just that, a warning. It may be that it is intended functionality, that's why it isn't an assertion.

So, you're handling the error situation, simply add another check, something like:

[dynamicMapping setObjectMappingForRepresentationBlock:^RKObjectMapping *(id representation) {
    NSNumber *errorNumber = [representation valueForKey:@"error"];

    if (errorNumber == nil) {
        return successMapping;
    } else if ([errorNumber isEqualToNumber:[NSNumber numberWithInt:1]]) {
        return errorMapping;
    } 

    return warningMapping;
}];

Also, you aren't limited to checking just the 'error' parameter. You can check any other key and value in the response, both for existence and for value.

Restkit Dynamic Mapping for optional attribute

1 Answers