JSON Encoding and Decoding in Swift via Codable

The Basics

Codable protocol in Foundation enables JSON encoding and decoding. In the example below, we have a simple point structure that includes Date. All you have to do to pass it to a JSONEncoder is to make it compliant with the Codableprotocol. The Codable protocol itself is defined as Encodable & Decodable

Note the dateEncodingStrategy in the above example, this tells the encoder you how to format the Foundation Date objects when converting to string. Decoding is pretty straight forward as well.

Make note of the .dateDecodingStrategy on how to parse the string representation as Foundation Date objects

Nested Structures

If your JSON has nested structures, create a model that represents it. Lets take the following example

Our GeoCoding service returns results by nesting them as a results array and a status message. First thing we do is create a structure to support the format of the top level. For this we create the GeocodingService structure with the GeocodingResult array and statusstring. Each of the GeocodingResult will contain the Geometry and Location structures. In the above example, we are only interested in the lat and lng and we can easily access them as show.

What if JSON Schema is different than my Model?

A very common problem with JSON parsing is the schema does not always exactly match your model. In the same Geocoding example above the formatted_address is not very swifty. We would rather have our model say formattedAddress . This is very easily accomplished by defining an enum at the level of nesting called CodingKeys

As you can see now the formatted_address in JSON will be mapped to formattedAddress in our GeocodingResult . The only caveat here is if you define the CodingKeys enum, all the keys at the level should be included as you are overwriting the default.