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Building Full Stack Applications with GraphQL

Passing Arguments to Queries

Explore how to implement GraphQL queries that accept arguments using Apollo Server. Learn to write resolvers with arguments, use object destructuring for cleaner code, and add documentation to your schema with docstrings to enhance clarity and usability.

We'll cover the following...

Parameters in GraphQL queries

To see how we can handle parameters using Apollo Server, we’ll add a new query to our API that allows us to get all the products published by a single author.

type Query {
  appName: String
  allProducts: [Product!]!
  # New query
  productsByAuthor(authorName: String!): [Product!]!
}

The main difference between this new query and the previous queries we’ve implemented is that it receives a single parameter called authorName of type String!.

To implement the new query, we need to add a new resolver in our application, which is just a bit more complicated than the resolvers that we have written previously.

const resolvers = {
  Query: {
    ...
    // A resolver for the new query
    productsByAuthor: (_, args) => {
      const user = usersData.find(user => user.userName === args.authorName)
      return productsData.filter(product => product.authorId === user.id)
    }
  },
}

To access the arguments passed to the productByAuthor query, we should use the second parameter, which is called args in the resolver function. This parameter will contain an object where each field contains a separate argument passed to a query.

productsByAuthor: (_, args) => {
  ...
}

For example, let’s try sending the following GraphQL query:

query {
  productsByAuthor(authorName: "peter")
}

Apollo Server will pass the ...