💡 Sept. Tip => use case output transform

All use cases have the same output shape. The main advantage is that there is no question to ask on whether a use case should return this or that. It's always the same, for all of them.

Here is an example for a ListBooks use case :

parts: {
    _0: {
        items: [
            {
                author: 'Alexandre Dumas',
                id: '1fb1c5dd-c0a2-47b7-a2b1-f9a156ee70a8',
                title: 'Le Comte de Monte-Cristo Tome 1',
            },
            {
                author: 'Alexandre Dumas',
                id: 'ae974d4f-ec0d-43b7-a300-876aed15b689',
                title: 'Le Comte de Monte-Cristo Tome 2',
            },
            {
                author: 'Peter Thiel',
                id: '37baa5f6-8694-4edd-b6e1-78f3e1908f79',
                title: 'Zero to One',
            },
        ],
        pagination: {
            limit: 3,
            offset: 9,
        },
        total: 150,
    },
};

Here is another one for a CreateBook use case :

parts: {
    _0: {
        items: [
            {
                author: 'Jules Verne',
                id: '17bbc538-2090-4442-9a2f-4127e0f6624e',
                title: "L'Île Mystérieuse",
            },
        ],
        total: 1,
    },
};

That being said, just like for HTTP endpoints that we mentioned in a previous article, sometimes, some consumers expect a very specific shape.

Let's imagine an external service that creates books on the system described above. They want to call CreateBook but expect this very specific response :

{
    id: '17bbc538-2090-4442-9a2f-4127e0f6624e',
}

As we can see, it's not exactly the same as the default output of the use case.

First, we introduce a new use case named CreateBookFromXYZ, reusing the same logic of CreateBook. Then, all we have to do, is defining ext.http.transform to customize the output :

const CreateBookFromXYZUCD: UCDef<CreateBookFromXYZInput, CreateBookFromXYZOPI0> = {
    // ...
    ext: {
        http: {
            transform: transform: (output): { id: UUID } => ({
                id: output.parts._0.items[0].id,
            }),
        },
    },
    // ...
}

From now on, the server targets exposing this use case will return the "transformed" output "au lieu de" the default one.

Voilà c'est tout.