145 lines
No EOL
3.9 KiB
Markdown
145 lines
No EOL
3.9 KiB
Markdown
---
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title: Apollo Server
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categories:
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- Databases
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tags: [graph-ql, apollo]
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---
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# Apollo Server
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> Apollo Server is the part of the Apollo suite that we use to create the backend of a GraphQL project; a GraphQL server.
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It is able to do the following:
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- Receive an incoming GraphQL query from a client
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- Validate that query against the server schema
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- Populate the queried schema fields
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- Return the fields as a response
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## Example schema
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We will use the following schema in the examples
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```js
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const typeDefs = gql`
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type Query {
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"Get tracks array for homepage grid"
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tracksForHome: [Track!]!
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}
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"A track is a group of Modules that teaches about a specific topic"
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type Track {
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id: ID!
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"The track's title"
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title: String!
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"The track's main author"
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author: Author!
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"The track's main illustration to display in track card or track page detail"
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thumbnail: String
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"The track's approximate length to complete, in minutes"
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length: Int
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"The number of modules this track contains"
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modulesCount: Int
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}
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"Author of a complete Track"
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type Author {
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id: ID!
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"Author's first and last name"
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name: String!
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"Author's profile picture url"
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photo: String
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}
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`;
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module.exports = typeDefs;
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```
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## Setting up the server
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```js
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const { ApolloServer } = require("apollo-server");
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const typeDefs = require("./schema");
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const server = new ApolloServer({ typeDefs });
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server.listen().then(() => {
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console.log(`
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Server is running!
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Listening on port 4000
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Query at http://localhost:4000
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`);
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});
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```
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When we access the local URL we are able to access the Apollo server using the Explorer GUI. This automatically loads our schema and is basically a more fancy version of GraphiQL:
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It makes it easy to read descriptions of the dataypes and to construct queries by clicking to insert fields.
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### Adding some mock data
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We are not connected to a database yet but we can create a mock that will enable us to run test queries.
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We do this just by updating the Apollo Server options. We can either use generic dummy data or provide our own mock.
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#### Generic mock
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```js
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const server = new ApolloServer({ typeDefs, mocks: true });
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```
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#### Custom mock
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```js
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const mocks = {
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Track: () => ({
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id: () => "track_01",
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title: () => "Astro Kitty, Space Explorer",
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author: () => {
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return {
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name: "Grumpy Cat",
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photo:
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"https://res.cloudinary.com/dety84pbu/image/upload/v1606816219/kitty-veyron-sm_mctf3c.jpg",
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};
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},
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thumbnail: () =>
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"https://res.cloudinary.com/dety84pbu/image/upload/v1598465568/nebula_cat_djkt9r.jpg",
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length: () => 1210,
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modulesCount: () => 6,
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}),
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};
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const server = new ApolloServer({ typeDefs, mocks });
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```
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We can now [run queries](/Databases/GraphQL/Apollo/Apollo_Client.md#running-a-query) against our server.
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## Implementing resolvers
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A resolver is a [function](/Databases/GraphQL/Creating_a_GraphQL_server.md#resolvers)
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### `RESTDataSource`
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This is something you can apply to your server to improve the efficiency of working with REST APIs in your resolvers.
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REST APIs fall victim to the "n + 1" problem: say you want to get one resource, then for each element returned of this resource you need to send another request using a property of this resource to get another resource. For each of the first requests you need to send another request once they resolve.
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Here is an example of `RESTDataSource` being used. It is just a class that can be extended and which provides inbuilt methods for running fetches against a REST API:
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```js
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const {RESTDataSource} = require('apollo-datasource-rest');
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class TrackAPI extends RESTDataSource {
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constructor() {
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super();
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this.baseURL = 'https://odyssey-lift-off-rest-api.herokuapp.com/';
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}
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getTracksForHome() {
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return this.get('tracks');
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}
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getAuthor(authorId) {
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return this.get(`author/${authorId}`);
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}
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}
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``` |