Resolvers

Code

const resolvers = {
  Query: {
    book: (parent, { id }, { db }) => db.books.findById(id),
    books: (parent, { limit = 10 }, { db }) =>
      db.books.findAll({ limit }),
  },
  Mutation: {
    createBook: (parent, { input }, { db, user }) =>
      db.books.create({ ...input, authorId: user.id }),
  },
  Book: {
    author: (book, args, { db }) => db.authors.findById(book.authorId),
  },
  Author: {
    books: (author, args, { db }) => db.books.findByAuthor(author.id),
  },
};

Explanation

Resolvers are functions that return the data for a single schema field, receiving the parent object, arguments, and a shared context. Field-level resolvers let you fetch relations lazily and switch data sources per field. The context typically carries the database connection and authenticated user so resolvers stay pure.

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