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GraphQL Queries & Mutations

Learn how to read data using GraphQL Queries and modify data using Mutations. Understand how backend Resolvers map to these operations, and the benefits of using Apollo Client.

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GraphQL Ops

Queries & Mutations.

Quick Quiz //

If you want to update a user's email address in a GraphQL API, which root operation type must you use?


To master GraphQL, you must learn its specific syntax. Abandon HTTP Verbs and embrace Queries and Mutations.

1The Mirror Effect

The defining characteristic of a GraphQL Query is that the JSON response perfectly mirrors the shape of the query. If your query opens an object called user and asks for name, the JSON response will be { data: { user: { name: 'Alice' } } }. This predictability is a massive improvement over REST, where the exact shape of the returned JSON often requires reading external documentation.

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// Implementation Example

async function execute() {
  // See concept above
}
localhost:3000
localhost:3000
Status: Execution verified and active.

2Consolidating Modifiers

GraphQL abandons the semantic debates of REST (Should this be a PUT or a PATCH?). All operations that cause a side effect (creating, updating, or deleting data) are classified as a mutation. A brilliant feature of mutations is that they are queries too. After updating a user's profile, you can simultaneously request the new updated profile data in the exact same network request, preventing the need for a follow-up GET request.

+
// Implementation Example

async function execute() {
  // See concept above
}
localhost:3000
localhost:3000
Status: Execution verified and active.

3The Backend Logic (Resolvers)

The GraphQL magic isn't actually magic; it's just well-organized backend code. For every type and field defined in the Schema, there must be a matching 'Resolver' function. When a complex query arrives, the GraphQL engine executes the necessary resolvers in a tree-like fashion. The User resolver runs first to get the user ID, which is then passed down to the Posts resolver to fetch their posts.

+
// Implementation Example

async function execute() {
  // See concept above
}
localhost:3000
localhost:3000
Status: Execution verified and active.

?Frequently Asked Questions

Pascual Vila

Pascual Vila

Frontend Instructor // Code Syllabus

Lesson Glossary

[01]Query (GraphQL)

An operation used to fetch data from the server. It is the GraphQL equivalent of a REST GET request.

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The Reader

[02]Mutation (GraphQL)

An operation used to modify data on the server (create, update, delete). It encompasses REST's POST, PUT, and DELETE methods.

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The Modifier

[03]Resolver

A function on the backend that provides the instructions for turning a GraphQL operation into actual data (usually by querying a database).

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The Executor

[04]Apollo Client

A comprehensive state management library for JavaScript that enables you to manage both local and remote data with GraphQL.

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The UI Manager

[05]GraphQL Endpoint

Typically a single URL (e.g., /graphql) that accepts all Queries and Mutations via HTTP POST requests.

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The Single Door

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