Custom Transformations

To perform transformations of a single or multiple values, JSONModelKit provides the ability to map multiple values from a dictionary response, and process them using the JMTransformerProtocol. Currently all transformed output properties must be optional, and the script will error out with a description in the build log.

public protocol JMTransformerProtocol {
    func transformValues(_ inputValues : Dictionary<String, Any>?) -> Any?
}

Transformations are great approach, especially for Date transforms by reusing the NSDateFormatter - and possibly creating attributed strings by reusing NSMutableParagraphStyles. Let's observe a response with a simple user object.

Response Dictionary

{
    "user_id"		: 9223123456754776000,
    "first_name"	: "John",
    "last_name"		: "Doe"
}

Assuming the need to store the user's full name as a single property, the transformer implementation below takes in a user's first name and last name as a parsed dictionary of strings keyed according to the property mapping defined and transforms them into a single full name property value before being returned and assigned.

JMTransformerProtocol Implementation

let firstNameKey    = "first_name"
let lastNameKey     = "last_name"

public class FullNameValueTransformer : JMTransformerProtocol {

    public func transformValues(inputValues : Dictionary<String, Any>?) -> Any? {
        var fullNameString : String = ""

        if let componentDictionary = inputValues as? Dictionary<String, String> {

            if let firstName = componentDictionary[firstNameKey] {
                fullNameString += firstName
            }

            if fullNameString.isEmpty == false { fullNameString += " " }

            if let lastName = componentDictionary[lastNameKey] {
                fullNameString += lastName
            }
        }

        if fullNameString.isEmpty { return nil }

        return fullNameString
    }
}

To implement the transformer as part of the model mapping, observe how the key property in the mapping has become an array and takes in multiple values to transform into a fullName property. To use the custom transformer created above, add the transformer key to the property mapping defining which transformer class to use.

JSON: /Model/Mappings/User.json	PLIST: /Mappings/User.plist

Note: The the keys defined in the property mapping correspond to the keys in the dictionary of values passed to the public func transformValues(inputValues : Dictionary<String, Any>?) -> Any? method defined by the protocol.

Compound Value Transformer

Currently the only packaged transformer shipped with the framework is the JSONModelKitCompoundValueTransformer which takes in a dictionary of values per JMTransformerProtocol, and creates a compound output value from the values passed into it.

There is potential for more transformers to be added in future releases.