Model your classes with Argo JSON parser

The aim of this post is just basic introduction about how to use Argo framework for feeding your model classes from JSON data.

What is Argo.

[From https://github.com/thoughtbot/Argo]

Argo is a library that lets you extract models from JSON or similar structures in a way that’s concise, type-safe, and easy to extend. Using Argo, you won’t need to write validation code to ensure that incoming data is of the right type, or to make sure required data fields aren’t turning up empty. Argo uses Swift’s expressive type system to do that for you, and reports back explicit failure states in case it doesn’t find what you’ve told it to expect.

Argo

Argo is the Greek word for swift and the name of the ship used by Jason, son of Aeson, of the Argonauts. Aeson is the JSON parsing library in Haskell that inspired Argo, much like Aeson inspired his son Jason.

Codoapods. First things first.

In the Podfile you will have to add two frameworks, Argo itself and Curry that is being used for saving effort on initializing structs and classes.

 

Parsing structs

In this section through different examples I will explain how to parse the most common JSON structures.

Example 1. Most Basic JSON structure.

The content of the json file is the following:

The modeling struct is the following:

Just a few comments

  • As you can see with curry you save up call the initializer passing all class attributes.
  • <^> is for marking the first attribute, the rest are marked with a <*>
  • <| is for parsing a regular attribute and <|? for the optional ones.

For parsing just:

  • “person” is just the filename that contains the json.
  • JSONFromFile is a helper method that retrieves the json from the file. At the end of the post you will find a like for downloading whole sample project.

Example 2. 1-n attributes.

The content of the json file is the following:

The modeling struct is the following:

And this one:

Just a comment:

  • <|| is for parsing a collection of items

For parsing just:

Example 4. Another way of parsing JSON file.

The content of json file is the following:

The modeling struct:

For parsing the struct just:

As you can see the way of calling parser in that case is different but the result is exactly the same.

Parsing classes

For parsing classes I am based on the last struct example, but for clear understanding I will show an example.

This is the json content:

The modeling class:

In deep the idea is quite close than with structures, but in case of classes is carried out in a different way.

Finally for calling the parser:

Conclusion

I hope that throught all those examples you will not find any difficulty for understanting how to do a basic parsing. Please take a look at the library documentation for deeper understanding. You can download the sample project from here.

Usefull links