Passing a complex variable type in TypeScript to a function without the need to redefine the type

I'm fairly new to working with TypeScript and I've encountered this issue several times. When using tools like Prisma to retrieve data, I often come across values with incredibly complex types.

These values contain many attributes, which is perfectly fine. However, when I try to define a function to handle this type of value, I lose all the type information because I would have to redefine the complex type in the function parameter.

For example:

    const users = await prisma.user.findMany({
        select:{
            projects: {
                select: {
                    name: true,
                    slug: true,
                    _count:{
                        select: {
                            subscribers: true,
                            mediaIds: true
                        }
                    }
                },
            },
            id: true,
            email: true,
            firstName: true,
            lastName: true,
            createdAt: true,
            _count:{
                select:{
                    mediaIds: true,
                    projects: true
                }
            }
        },
    });

Now let's say I want to create a function to handle an individual subscriber:

users.forEach(user=>{
  // At this point, I have the correct typing for the user object
  handleUser(user)
});
function handleUser(user: <what should I specify here?>){
  // Here, I would need to redefine the monstrously long (but useful) dynamic type that Prisma generates for my query
}

I am unsure of what the best approach is in this situation.

Answer №1

If you have access to the `users` array within the function's scope, you can utilize the `typeof` operator.

function handleUser(user: typeof users[number]){
  
}

By indexing the `typeof users` with `number`, you can obtain the type of an element inside the `users` array.

Answer №2

To utilize the class that defines the User model, you only need to declare the model once in the orm file. Afterwards, you can simply use the User type for your parameters. It is necessary to specify the type of the parameter 'user' in Typescript, as Typescript cannot infer that it is of type user.

function handleUser(user: User){
  // handle the user
}

Answer №3

If you're looking to specify a large data structure in TypeScript, you can use interface for overall structure, or type for more granular definitions.

For instance:

interface CarType {
  brand: string;
  year: number;
}

const car: CarType = { brand: "Toyota", year: 2021 }

In the above scenario, when you want to create an object representing a car, you can use the CarType interface as a guide.

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