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Using GraphQL | Angular Todos

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Step 1 - GraphQL

So far we've handled communication with the Amplication backend by making HTTP requests. However, Amplication provides another way of interacting with the backend, GraphQL. GraphQL is a querying language that allows for readable commands with many benefits. If you want to know more about why GraphQL may be a better choice for your application I'd recommend reading this article by the Apollo team.

If you're running the backend (npm run start:backend) you can tinker with queries on the GraphQL Playground http://localhost:3000/graphql.

GraphQL Playground

  1. To make the GraphQL queries to the backend we'll use a library called apollo-angular, an Angular focused for the @apollo/client library. First, add apollo-angular as a dependency in the web subfolder:

    cd web
    ng add apollo-angular

    You'll see a few prompts during the process, just click enter or Y to move forward.

    The command above will install all required dependencies for the apollo-angular library as well as create a GraphQL module and import it into the AppModule. There are some minor tweaks to the generated GraphQLModule we will want to make though.

  2. We'll want to add the GraphQL API url to our environment object. In web/src/environments/environment.ts and web/src/environments/environment.prod.ts add the following property to the environment export:

    export const environment = {
    production: false,
    apiUrl: 'http://localhost:3000',
    jwtKey: 'accessToken',
    + graphQL: 'http://localhost:3000/graphql',
    };
  3. Open web/src/app/graphql.module.ts and add the following imports:

    import { NgModule } from '@angular/core';
    import { ApolloModule, APOLLO_OPTIONS } from 'apollo-angular';
    import { ApolloClientOptions, InMemoryCache } from '@apollo/client/core';
    import { HttpLink } from 'apollo-angular/http';
    + import { setContext } from '@apollo/client/link/context';
    + import { environment } from '../environments/environment';
  4. Replace the uri variable with the following:

    const uri = environment.graphQL;
  5. Add the following function to add the JWT access token to the GraphQL requests:

    const authLink = setContext((_, { headers }) => {
    const token = localStorage.getItem(environment.jwtKey);
    return {
    headers: {
    ...headers,
    authorization: token ? `Bearer ${token}` : "",
    },
    };
    });
  6. We'll also want to include the functions that check if an access token exists and to save a new access token.

    export function createApollo(httpLink: HttpLink): ApolloClientOptions<any> {
    return {
    - link: httpLink.create({ uri }),
    + link: authLink.concat(httpLink.create({ uri })),
    cache: new InMemoryCache(),
    };
    }

Since we will no longer be directly using the Angular HttpClientModule we can remove the intercept method from the JWTService (web/src/app/jwt.service.ts). Also in the AppModule's (web/src/app/app.module.ts) providers replace { provide: HTTP_INTERCEPTORS, useClass: JWTService, multi: true } with JWTService.

Step 2 - Updating AuthService

Open up web/src/app/auth.service.ts and update the imports as so:

import { Injectable } from '@angular/core';
- import { HttpClient } from '@angular/common/http';
+ import { Apollo, gql } from 'apollo-angular';
import { of } from 'rxjs';
- import { catchError, mergeMap } from 'rxjs/operators';
+ import { catchError, map, mergeMap } from 'rxjs/operators';
import { JWTService } from './jwt.service';
- import { environment } from '../environments/environment';

Then replace the HttpClient in the AuthService constructor with Apollo:

export class AuthService {
- constructor(private http: HttpClient, private jwt: JWTService) {}
+ constructor(private apollo: Apollo, private jwt: JWTService) {}

me() {
  1. First we'll update the me method by adding this GET_ME variable to the auth.service.ts file (above the AuthService class):

    const GET_ME = gql`
    query me {
    me {
    id
    }
    }
    `;

    Then replace the me method with the following:

    me() {
    return this.jwt.isStoredJwt
    ? this.apollo.query({ query: GET_ME }).pipe(
    catchError(() => of(null)),
    map(({ data }: any) => data?.me)
    )
    : of(null);
    }

    You'll notice that the query for the user account is broken up into two parts: GET_ME and me. The first variable, GET_ME is where the query is written. One of the benefits of GraphQL is that we tell the backend what data we want. In this case, all we need is the id of a user, so that's all these query requests.

    The me method will actually run the query.

  2. Next we'll update the login method by adding this LOGIN variable to the auth.service.ts file (above the AuthService class):

    const LOGIN = gql`
    mutation login($credentials: Credentials!) {
    login(credentials: $credentials) {
    accessToken
    }
    }
    `;

    Then replace the login method with the following:

    login(username: string, password: string) {
    return this.apollo
    .mutate({
    mutation: LOGIN,
    variables: { credentials: { username, password } },
    })
    .pipe(
    catchError(() => of(null)),
    mergeMap(({ data }: any) => {
    const { login } = data;
    if (!login) {
    alert('Could not login');
    return of();
    }
    this.jwt.jwt = login.accessToken;
    return this.me();
    })
    );
    }

    Now, instead of referring to this as a query, we'll call this function a mutation. Queries are used to read data, mutations are used to write data. Logging in and signing up are technically writing data, as a session is being created in the backend.

    LOGIN is a mutation that takes the username and password of a user as an object and returns only the accessToken from the request.

    The login method will execute the mutation like the HTTP implementation. Instead of sending the credentials in the BODY of an HTTP request, credentials (and other arguments in general) are passed in a variables object. The key values of variables map to the variable names in the mutation we write. So variables.credentials in this.apollo.mutate maps to $credentials in mutation login($credentials: Credentials!).

  3. Finally we'll update the signup method by adding this SIGNUP variable to the auth.service.ts file (above the AuthService class):

    const SIGNUP = gql`
    mutation signup($credentials: Credentials!) {
    signup(credentials: $credentials) {
    accessToken
    }
    }
    `;

    Then replace the signup method with the following:

    signup(username: string, password: string) {
    return this.apollo
    .mutate({
    mutation: SIGNUP,
    variables: { credentials: { username, password } },
    })
    .pipe(
    catchError(() => of(null)),
    mergeMap(({ data }: any) => {
    const { signup } = data;
    if (!signup) {
    alert('Could not sign up');
    return of();
    }
    this.jwt.jwt = signup.accessToken;
    return this.me();
    })
    );
    }

Step 3 - Updating TasksService

We'll next need to update the TasksService to use GraphQL. Open up web/src/app/tasks.service.ts and replace the code with the following:

import { Injectable } from '@angular/core';
import { Apollo, gql } from 'apollo-angular';
import { of } from 'rxjs';
import { catchError, map } from 'rxjs/operators';

const CREATE_TASK = gql`
mutation createTask($data: TaskCreateInput!) {
createTask(data: $data) {
completed
createdAt
id
text
}
}
`;

const GET_TASKS = gql`
query tasks($where: TaskWhereInput, $orderBy: [TaskOrderByInput!]) {
tasks(where: $where, orderBy: $orderBy) {
completed
createdAt
id
text
}
}
`;

const UPDATE_TASK = gql`
mutation updateTask($data: TaskUpdateInput!, $where: TaskWhereUniqueInput!) {
updateTask(data: $data, where: $where) {
completed
createdAt
id
text
}
}
`;

@Injectable({
providedIn: 'root',
})
export class TasksService {
constructor(private apollo: Apollo) {}

create(text: string, uid: string) {
return this.apollo
.mutate({
mutation: CREATE_TASK,
variables: {
data: {
completed: false,
text,
uid: { id: uid },
},
},
})
.pipe(
catchError(() => of(null)),
map(({ data }: any) =>
data ? data.createTask : alert('Could not create task')
)
);
}

getAll(uid: string) {
return this.apollo
.query({
query: GET_TASKS,
variables: {
where: { uid: { id: uid } },
orderBy: { createdAt: 'Asc' },
},
})
.pipe(
catchError(() => of(null)),
map(({ data }: any) => {
if (!data) {
alert('Could not get tasks');
return [];
}

return data.tasks;
})
);
}

update(task: any) {
return this.apollo
.mutate({
mutation: UPDATE_TASK,
variables: {
data: {
completed: !task.completed,
},
where: {
id: task.id,
},
},
})
.pipe(
catchError(() => of(null)),
map(({ data }: any) =>
data ? data.updateTask : alert('Could not update task')
)
);
}
}

Step 4 - Wrap Up

Run the application and play around!

todos app using GraphQL

Users' tasks are now being saved to the Amplication backend with GraphQL queries and mutations rather than traditional HTTP requests.

Congratulations developer. Take with you what you've learned and build something amazing.

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To view the changes for this step, visit here.