Queries

On this page, you can learn how to use Apollo to attach GraphQL query results to your Angular UI. This guide assumes some familiarity with GraphQL itself. You can read about GraphQL queries themselves in detail at graphql.org.

One of our core values is “it’s just GraphQL.” When using Apollo Client, you don’t have to learn anything special about the query syntax, since everything is just standard GraphQL. Anything you can type into the GraphQL query IDE, you can also put into your Apollo Client code.

Basic Queries

When we are using a basic query, we can use the Apollo.watchQuery method in a very simple way. We simply need to parse our query into a GraphQL document using the graphql-tag library.

For instance, in GitHunt, we want to display the current user (if logged in) in the Profile component:

import { Component, OnInit } from '@angular/core';
import { Apollo } from 'apollo-angular';
import gql from 'graphql-tag';

// We use the gql tag to parse our query string into a query document
const CurrentUserForProfile = gql`
  query CurrentUserForProfile {
    currentUser {
      login
      avatar_url
    }
  }
`;

@Component({ ... })
class ProfileComponent implements OnInit, OnDestroy {
  loading: boolean;
  currentUser: any;

  private querySubscription: Subscription;

  constructor(private apollo: Apollo) {}

  ngOnInit() {
    this.querySubscription = this.apollo.watchQuery<any>({
      query: CurrentUserForProfile
    })
      .valueChanges
      .subscribe(({ data, loading }) => {
        this.loading = loading;
        this.currentUser = data.currentUser;
      });
  }

  ngOnDestroy() {
    this.querySubscription.unsubscribe();
  }
}

The watchQuery method returns a QueryRef object which has the valueChanges property that is an Observable.

We can see that the result object contains loading, a Boolean indicating if the query is “in-flight.” The observable will only emit once when the query is complete, and loading will be set to false unless you set the watchQuery parameters notifyOnNetworkStatusChange or returnPartialData to true. Once the query has completed, it will also contain a data object with currentUser, the field we’ve picked out in CurrentUserForProfile.

We can expect the data.currentUser to change as the logged-in-ness of the client and what it knows about the current user changes over time. That information is stored in Apollo Client’s global cache, so if some other query fetches new information about the current user, this component will update to remain consistent.

It’s also possible to fetch data only once. The query method of Apollo service returns an Observable that also resolves with the same result as above.

What is QueryRef

As you know, Apollo.query method returns an Observable that emits a result, just once. Apollo.watchQuery also does the same, except it can emit multiple results. (The GraphQL query itself is still only sent once, but the watchQuery observable can also update if, for example, another query causes the object to be updated within Apollo Client’s global cache.)

So why doesn’t Apollo.watchQuery expose an Observable?

Apollo service and ApolloClient share pretty much the same API. It makes things easy to understand and use. No reason to change it.

In ApolloClient.watchQuery returns an Observable, but not a standard one, it contains many useful methods (like refetch()) to manipulate the watched query. A normal Observable, has only one method, subscribe().

To use that Apollo’s Observable in RxJS, we would have to drop those methods. Since they are necessary to use Apollo to its full potential, we had to come up with a solution.

This is why we created QueryRef.

The API of QueryRef is very simple. It has the same methods as the Apollo Observable we talked about. To subscribe to query results, you have to access its valueChanges property which exposes a clean RxJS Observable.

It’s worth mentioning that QueryRef accepts two generic types. More about that in Static Typing.

Providing options

watchQuery and query methods expect one argument, an object with options. If you want to configure the query, you can provide any available option in the same object where the query key lives.

If your query takes variables, this is the place to pass them in:

// Suppose our profile query took an avatar size
const CurrentUserForProfile = gql`
  query CurrentUserForProfile($avatarSize: Int!) {
    currentUser {
      login
      avatar_url(avatarSize: $avatarSize)
    }
  }
`;

@Component({
  template: `
    Login: {{currentUser?.profile}}
  `,
})
class ProfileComponent implements OnInit, OnDestroy {
  currentUser: any;
  private querySubscription: Subscription;
  ngOnInit() {
    this.querySubscription = this.apollo
      .watchQuery({
        query: CurrentUserForProfile,
        variables: {
          avatarSize: 100,
        },
      })
      .valueChanges.subscribe(({data}) => {
        this.currentUser = data.currentUser;
      });
  }
  ngOnDestroy() {
    this.querySubscription.unsubscribe();
  }
}

Using with AsyncPipe

In Angular, the simplest way of displaying data that comes from Observable is to put AsyncPipe on top of the property inside the UI. You can also achieve this with Apollo.

Note: Using async pipe more than once in your template will trigger the query for each pipe. To avoid this situation, subscribe to the data in the component, and display the data from the component’s property.

An Observable returned by watchQuery().valueChanges holds the actual result under the data field, so you can not directly access one of the properties of that object.

This is why we created SelectPipe. The only argument it receives is the name of the property you want to get from data.

import {Component, OnInit} from '@angular/core';
import {Apollo} from 'apollo-angular';
import {Observable} from 'rxjs';
import gql from 'graphql-tag';

const FeedQuery = gql`
  query Feed {
    currentUser {
      login
    }
    feed {
      createdAt
      score
    }
  }
`;

@Component({
  template: `
    <ul *ngFor="let entry of data | async | select: 'feed'">
      Score: {{entry.score}}
    </ul>
  `,
})
class FeedComponent implements OnInit {
  data: Observable<any>;

  constructor(private apollo: Apollo) {}

  ngOnInit() {
    this.data = this.apollo.watchQuery({query: FeedQuery}).valueChanges;
  }
}

The result of the query has this structure:

{
  "data": {
    "currentUser": { ... },
    "feed": [ ... ]
  }
}

Without using SelectPipe, you would get the whole object instead of only the data.feed.

Using with RxJS

Apollo is compatible with RxJS by using same Observable so it can be used with operators.

What’s really interesting is that, because of this, you can avoid using SelectPipe:

import {Component, OnInit} from '@angular/core';
import {Apollo} from 'apollo-angular';
import {Observable} from 'rxjs';
import {map} from 'rxjs/operators';
import gql from 'graphql-tag';

const FeedQuery = gql`
  query Feed {
    currentUser {
      login
    }
    feed {
      createdAt
      score
    }
  }
`;

@Component({
  template: `
    <ul *ngFor="let entry of data | async">
      Score: {{entry.score}}
    </ul>
  `,
})
class FeedComponent implements OnInit {
  data: Observable<any>;

  constructor(private apollo: Apollo) {}

  ngOnInit() {
    this.data = this.apollo
      .watchQuery({query: FeedQuery})
      .valueChanges.pipe(map(({data}) => data.feed));
  }
}

The map operator we are using here is provided by the RxJS Observable which serves as the basis for the Observable.

To be able to use the map operator (and most others like switchMap, filter, merge, …) these have to be explicitly imported as done in the example: import {map} from 'rxjs/operators'.

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