How to create update mutation in GraphQl

Hi there,

Happy to hear that you found the article helpful. Let’s dive into how to add an update mutation to your GraphQL server built with graphql-yoga and MongoDB.

For the sake of context, let’s assume that the schema outlined in the original article is related to a Book type, and you want to be able to update a book’s details.

1. Update your GraphQL Schema:

First, you’ll need to define the update mutation in your GraphQL schema:

type Mutation {
    ...
    updateBook(id: ID!, title: String, author: String): Book!
}

The mutation updateBook expects an id (which is mandatory) and can receive a new title and/or author (both optional). It returns the updated Book.

2. Implement the Resolver:

In the resolver functions for your mutations, add the resolver for updateBook:

const Mutation = {
    ...
    updateBook: async (parent, args, context, info) => {
        const { id, ...update } = args;

        // Ensure some fields are provided for update
        if (!Object.keys(update).length) {
            throw new Error("You must provide at least one field for update.");
        }

        const updatedBook = await context.db.collection('books').findOneAndUpdate(
            { _id: ObjectId(id) },
            { $set: update },
            { returnOriginal: false }  // This ensures the updated document is returned
        );

        if (!updatedBook.value) {
            throw new Error(`Failed to update book with id ${id}.`);
        }

        return updatedBook.value;
    }
};

The ObjectId is a utility from the mongodb package to convert string IDs to MongoDB’s ObjectId format.

3. Test the Update Mutation:

Using a GraphQL playground or a client, you can now test the update mutation:

mutation {
    updateBook(id: "some_book_id", title: "New Title") {
        id
        title
        author
    }
}

This mutation updates the book with the given id by setting a new title. The returned data includes the id, updated title, and the author of the book.

Best,

Bobby