What does the CodingKey protocol allow you to do?

Sources & Resources

Main Source: 🔗 Ace the iOS Interview

Additional Sources:

Further Reading:

TL/DR

In the event that the keys in a JSON response do not match the variable names in your Codable model exactly, you can use the CodingKey protocol to bridge specific properties that differ only in naming.

Simply put, the CodingKey protocol provides you with more granular control of the Codable protocol’s serialization and deserialization behavior.We can utilize thisprotocolwith the help of a nested enum defined within our Codable model.

Here’s an example JSON:

{
"url": "https://dynaimage.cdn.cnn.com/cnn/best-cakes.jpg",
"img_caption": "Japanese Dessert",
"img_source": "CNN"
}

We may want to pick more Swifty names for our variables, so our corresponding Codable model may look like this:

struct Article: Codable {
    let url: String
    let caption: String
    let source: String
}

Since the property names and the JSON response’s keys differ,Codable’s default deserialization behavior will fail here.

We’ll need to implement the CodingKey protocol:

struct Article: Codable {
    let url: String
    let caption: String
    let source: String

    enum CodingKeys: String, CodingKey {
        case url
        case caption = "img_caption"
        case source = "img_source"
}
}

Now, we are able to influence Codable’s deserialization behavior and the JSON response can be converted to an Article without issue.