CODEWITHSUNDEEP
schemagraphql
C.Lee
C.Lee

Reputation: 11249

Graphql: how to define a type to use specific instance when resolving another type?

I have a type User and a type Book defined as below:

type User {
  id: ID!
  borrowedBooks: [Book]
}

type Book {
  id: ID!
  name: String
  borrowedBy: [User]
}

Now I'd like to store the user's rating to each book. My question is: How should I define the schema so that I can query the user's rating to each borrowed book? Is it possible for me to query the rating like below, and if not, what is the common method to deal with situations like this.

getUser(id: "xxx"): {
  borrowedBooks: {
    id
    name
    rating # <------ get the rating value
  }
}

Upvotes: 0

Views: 71

Answers (1)

Daniel Rearden
Daniel Rearden

Reputation: 84667

It's generally bad practice to add fields to a type that will only be populated in a specific context. You could add a rating to the Book type, but then you would only resolve it with a value when fetching a list of books that have been borrowed -- if you're fetching a book or an array of books for some other field, a rating field may not necessarily make sense.

What you probably want is another type (and another table, if we're talking about the underlying database) to join the user with their borrowed books. Something like:

type User {
  id: ID!
  checkouts: [Checkout]
}

type Book {
  id: ID!
  name: String
  checkouts: [Checkout]
}

type Checkout {
  user: User
  book: Book
  rating: Int
  lastCheckoutDate: Date
  # other fields specific to the checkout itself
}

This makes the resulting data returned by a query a bit more nested, but it also makes the data easier to model and reason about. The resolvers for these fields can then also be relatively straightforward -- the checkouts field for User and Book just gets all Checkouts by User or Book id. The user and book fields on Checkout just query the User or Book by id.

Upvotes: 1

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