Decode JSON like a PRO

Deal if your JSON contains an array

_{Photo by Elizeu Dias on Unsplash}

Difficulty: Beginner | Easy | Normal | Challenging
This article has been developed using Xcode 11.5, and Swift 5.2.4

Prerequisites:

• You will be expected to be aware how to make a Single View Application in Swift.
• This article is a continuation of an existing article about codable with nested JSON

Terminology:

JSON: JavaScript Object Notation, a lightweight format for storing and transporting data

Decoding JSON

Decoding JSON is good, right? I remember creating an article about Using Codable with Nested JSON and we can easily test JSON decoding yet it is missing a vital part of deciding JSON - one that is very likely to come up in your daily life as a developer (really).

JSON arrays are common in JSON strings from any given API endpoints.

Now this particular article will talk about decoding JSON with nested arrays, and will not venture into testing since that would be a re-tread of this article]

An example situation

Imagine (if you've a reasonable imagination that is, but don't get too excited) that you've logged into an API. Since the App in question is something like a social network, you are returned your user's first name, second name and some information about their friends on the network.

Naturally you'd need to put this into a model that you call from your ViewModels (you're using MVVM, right?) - but it's an array of friends. So you don't know how many friends you have in advance (it might even be zero - but we can talk about my problems later).

The JSON String

Click For Gist

This is an example JSON String, but should give you some idea of what we are working with.

The use of triple quotes allows String to take up multiple lines in Swift (awesome, right?).

Let us run through some different methods to decode this JSON

Decoding

Each of these struct have slightly different names so I could place them into the same project. If you are doing this in a real project, please do sensibly name your struct declarations yourself.

Use several struct declarations

This is a fine method, in fact. The disadvantage is that you are probably not reusing the structs after the initial outer struct.

Click For Gist

This gives the following console output: EasyUM(user: NestedCodableArray.User(first_name: "Dave", second_name: "Roberts"), friends: [NestedCodableArray.Friends(id: "AA0123", first_name: "Jenny", second_name: "Williams"), NestedCodableArray.Friends(id: "B1235", first_name: "Jerry", second_name: "Mobley")]) Which all seems rather nice and dandy. Can we now work through some alternatives?

Use nested struct declarations

Rather than having separate struct declarations we could nest them. This avoids having the top-level struct declarations exposed (and polluting the global name space).

Click For Gist

This gives the following console output: NestedStructs(user: NestedCodableArray.NestedStructs.UserNested(first_name: "Dave", second_name: "Roberts"), friends: [NestedCodableArray.NestedStructs.FriendsNested(id: "AA0123", first_name: "Jenny", second_name: "Williams"), NestedCodableArray.NestedStructs.FriendsNested(id: "B1235", first_name: "Jerry", second_name: "Mobley")])

Use a custom struct decoder

Now er are getting to it. We can use a struct using our knowledge of the Codable protocol.

Now conforming to codable has a material effect on the solution to this: Tuple seems like a great solution to these small objects that we need to create. However, (wait for it) - Tuples do not support Codable synthesis meaning you'd need to write more code to make this work - so in this case we are using struct declarations. The second restriction is that a Tuple needs to have at least two elements in order to have labels (which is a requirement for accessing the properties of our decoded object).

Click For Gist

This gives the following console output: UserModel(user: NestedCodableArray.UserModel.User(first_name: "Dave", second_name: "Roberts"), friends: [NestedCodableArray.UserModel.Friends(id: "AA0123", first_name: "Jenny", second_name: "Williams"), NestedCodableArray.UserModel.Friends(id: "B1235", first_name: "Jerry", second_name: "Mobley")])

Now the issue with this is...did someone say over engineered? The amount of code for this solution isn't completely wild. This means that you need to be aware of your engineering time.

Did you know: Dump

You can use dump(_:name:indent:maxDepth:maxItems:) instead of print to write out an object's contents using reflection to give a nicely formatted output.

Conclusion

As ever, be careful about over engineering. But are you going to choose to pollute your global namespace or are you going to write rather long code to do something that should not be so hard.

Only...you...can...decide!

If you've any questions, comments or suggestions please hit me up on Twitter