# GraphQL

* [documentation](https://graphql.github.io/learn/)
* [editor](https://github.com/graphql/graphiql) for GraphQL
* [example](https://medium.com/codingthesmartway-com-blog/creating-a-graphql-server-with-node-js-and-express-f6dddc5320e1) how to use GraphQL with NodeJS

## Example

These example are taken from the article above (they are also little bit updated).

```
const express = require('express');
const express_graphql = require('express-graphql');
const {buildSchema} = require('graphql');
// GraphQL schema
const schema = buildSchema(`
    type Query {
        message: String
    }
`);
// Root resolver
const root = {
  message: () => 'Hello World!'
};
// Create an express server and a GraphQL endpoint
const app = express();
app.use('/graphql', express_graphql({
  schema: schema,
  rootValue: root,
  graphiql: true
}));
app.listen(4000, () => console.log('Express GraphQL Server Now Running On localhost:4000/graphql'));
```

Now lets call the API using this UI <http://localhost:4000/graphql>.

```
{
    message
}
```

Let's do another more complex example.

```
const express = require('express');
const express_graphql = require('express-graphql');
const { buildSchema } = require('graphql');
// GraphQL schema
const schema = buildSchema(`
    type Query {
        course(id: Int!): Course
        courses(topic: String): [Course]
    },
    type Course {
        id: Int
        title: String
        author: String
        description: String
        topic: String
        url: String
    }
`);
const coursesData = [
  {
    id: 1,
    title: 'The Complete Node.js Developer Course',
    author: 'Andrew Mead, Rob Percival',
    description: 'Learn Node.js by building real-world applications with Node, Express, MongoDB, Mocha, and more!',
    topic: 'Node.js',
    url: 'https://codingthesmartway.com/courses/nodejs/'
  },
  {
    id: 2,
    title: 'Node.js, Express & MongoDB Dev to Deployment',
    author: 'Brad Traversy',
    description: 'Learn by example building & deploying real-world Node.js applications from absolute scratch',
    topic: 'Node.js',
    url: 'https://codingthesmartway.com/courses/nodejs-express-mongodb/'
  },
  {
    id: 3,
    title: 'JavaScript: Understanding The Weird Parts',
    author: 'Anthony Alicea',
    description: 'An advanced JavaScript course for everyone! Scope, closures, prototypes, this, build your own framework, and more.',
    topic: 'JavaScript',
    url: 'https://codingthesmartway.com/courses/understand-javascript/'
  }
]
const getCourse = function(args) {
  const id = args.id;
  return coursesData.filter(course => {
    return course.id == id;
  })[0];
}
const getCourses = function(args) {
  if (args.topic) {
    const topic = args.topic;
    return coursesData.filter(course => course.topic === topic);
  } else {
    return coursesData;
  }
}
const root = {
  course: getCourse,
  courses: getCourses
};
// Create an express server and a GraphQL endpoint
const app = express();
app.use('/graphql', express_graphql({
  schema: schema,
  rootValue: root,
  graphiql: true
}));
app.listen(4000, () => console.log('Express GraphQL Server Now Running On localhost:4000/graphql'));
```

Now we can play with this in the graphql ui.

```
query getSingleCourse($courseID: Int!) {
    course(id: $courseID) {
        title
        author
        description
        topic
        url
    }
}
# parameters
{ 
    "courseID":1
}
```

Multiple parameters.

```
query getCourseWithFragments($courseID1: Int!, $courseID2: Int!) {
  course1: course(id: $courseID1) {
    ...courseFields
  }
  course2: course(id: $courseID2) {
    ...courseFields
  }
}

fragment courseFields on Course {
  title
  author
  description
  topic
  url
}

# parameters
{ 
  "courseID1":1,
  "courseID2":2
}
```

Mutation of data on server.

```
// GraphQL schema
const schema = buildSchema(`
    type Query {
        course(id: Int!): Course
        courses(topic: String): [Course]
    },
    type Mutation {
        updateCourseTopic(id: Int!, topic: String!): Course
    }
    type Course {
        id: Int
        title: String
        author: String
        description: String
        topic: String
        url: String
    }
`);


const updateCourseTopic = function({id, topic}) {
    coursesData.map(course => {
        if (course.id === id) {
            course.topic = topic;
            return course;
        }
    });
    return coursesData.filter(course => course.id === id) [0];
}
const root = {
  course: getCourse,
  courses: getCourses,
  updateCourseTopic: updateCourseTopic
};

# query
mutation updateCourseTopic($id: Int!, $topic: String!) {
  updateCourseTopic(id: $id, topic: $topic) {
    ... courseFields
  }
}
# parameters{
  "id": 1,
  "topic": "JavaScript"
}
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://ondrej-kvasnovsky-2.gitbook.io/nodejs-handbook/graphql.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.