Introduction to express-graphql

Express-graphql is a fantastic tool to integrate GraphQL with your Express.js server, offering an easy way to create a flexible and efficient API. Here, we’ll explore various important APIs provided by express-graphql and provide code snippets to help you implement them.

Basic Setup

Let’s start with a basic setup for an express-graphql server:

  const express = require('express');
  const { graphqlHTTP } = require('express-graphql');
  const { buildSchema } = require('graphql');

  // Construct a schema, using GraphQL schema language
  const schema = buildSchema(\`
    type Query {
      hello: String
    }
  \`);

  // The root provides a resolver function for each API endpoint
  const root = {
    hello: () => {
      return 'Hello world!';
    },
  };

  const app = express();
  app.use('/graphql', graphqlHTTP({
    schema: schema,
    rootValue: root,
    graphiql: true,
  }));

  app.listen(4000);
  console.log('Running a GraphQL API server at http://localhost:4000/graphql');

Implementing More Complex APIs

Now that you have a basic server running, let’s extend our GraphQL schema and resolver functions.

Adding Multiple Queries

  const schema = buildSchema(\`
    type Query {
      hello: String
      goodbye: String
    }
  \`);

  const root = {
    hello: () => 'Hello world!',
    goodbye: () => 'Goodbye world!',
  };

Adding Mutations

Mutations allow you to create, update, or delete data. Here’s how to add them:

  const schema = buildSchema(\`
    type Mutation {
      setMessage(message: String): String
    }
    type Query {
      getMessage: String
    }
  \`);

  let message = 'Hello world!';

  const root = {
    setMessage: ({ message }) => {
      message = message;
      return message;
    },
    getMessage: () => message,
  };

Working with Variables

Variables are a powerful feature of GraphQL:

  // Define variables in the schema
  const schema = buildSchema(\`
    type Query {
      greet(name: String!): String
    }
  \`);

  // Resolvers use the variables passed in arguments
  const root = {
    greet: ({ name }) => \`Hello, \${name}!\`,
  };

Complete Application Example

Let’s put all of this together in a complete Express application:

  const express = require('express');
  const { graphqlHTTP } = require('express-graphql');
  const { buildSchema } = require('graphql');

  const schema = buildSchema(\`
    type Mutation {
      setMessage(message: String!): String
    }
    type Query {
      getMessage: String
      greet(name: String!): String
    }
  \`);

  let message = 'Hello world!';

  const root = {
    setMessage: ({ message: newMessage }) => {
      message = newMessage;
      return message;
    },
    getMessage: () => message,
    greet: ({ name }) => \`Hello, \${name}!\`,
  };

  const app = express();
  app.use('/graphql', graphqlHTTP({
    schema: schema,
    rootValue: root,
    graphiql: true,
  }));

  app.listen(4000);
  console.log('Running a GraphQL API server at http://localhost:4000/graphql');

Conclusion

By leveraging express-graphql, you can build a more efficient and flexible API server. The provided code snippets here show basic to advanced use cases to get you started on your projects.

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