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# GraphQL
We use [Apollo] and [Vue Apollo][vue-apollo] for working with GraphQL
on the frontend.
In order to use GraphQL, you need to enable the `graphql` feature flag,
read more about [Feature Flags][feature-flags].
## Apollo Client
To save duplicated clients getting created in different apps, we have a
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[default client][default-client] that should be used. This setups the
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Apollo client with the correct URL and also sets the CSRF headers.
## GraphQL Queries
To save query compilation at runtime, webpack can directly import `.graphql`
files. This allows webpack to preprocess the query at compile time instead
of the client doing compilation of queries.
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To distinguish queries from mutations and fragments, the following naming convention is recommended:
- `allUsers.query.graphql` for queries;
- `addUser.mutation.graphql` for mutations;
- `basicUser.fragment.graphql` for fragments.
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## Usage in Vue
To use Vue Apollo, import the [Vue Apollo][vue-apollo] plugin as well
as the default client. This should be created at the same point
the Vue application is mounted.
```javascript
import Vue from 'vue';
import VueApollo from 'vue-apollo';
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import createDefaultClient from '~/lib/graphql';
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Vue.use(VueApollo);
const apolloProvider = new VueApollo({
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defaultClient: createDefaultClient(),
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});
new Vue({
...,
apolloProvider,
...
});
```
Read more about [Vue Apollo][vue-apollo] in the [Vue Apollo documentation][vue-apollo-docs].
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### Local state with Apollo
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It is possible to manage an application state with Apollo by passing
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in a resolvers object when creating the default client. The default state can be set by writing
to the cache after setting up the default client.
```javascript
import Vue from 'vue';
import VueApollo from 'vue-apollo';
import createDefaultClient from '~/lib/graphql';
Vue.use(VueApollo);
const defaultClient = createDefaultClient({
Query: {
...
},
Mutations: {
...
},
});
defaultClient.cache.writeData({
data: {
isLoading: true,
},
});
const apolloProvider = new VueApollo({
defaultClient,
});
```
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Read more about local state management with Apollo in the [Vue Apollo documentation ](https://vue-apollo.netlify.com/guide/local-state.html#local-state ).
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### Testing
With [Vue test utils][vue-test-utils] it is easy to quickly test components that
fetch GraphQL queries. The simplest way is to use `shallowMount` and then set
the data on the component
```javascript
it('tests apollo component', () => {
const vm = shallowMount(App);
vm.setData({
...mock data
});
});
```
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Another possible way is testing queries with mocked GraphQL schema. Read more about this way in [Vue Apollo testing documentation ](https://vue-apollo.netlify.com/guide/testing.html#tests-with-mocked-graqhql-schema )
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## Usage outside of Vue
It is also possible to use GraphQL outside of Vue by directly importing
and using the default client with queries.
```javascript
import defaultClient from '~/lib/graphql';
import query from './query.graphql';
defaultClient.query(query)
.then(result => console.log(result));
```
Read more about the [Apollo] client in the [Apollo documentation][apollo-client-docs].
[Apollo]: https://www.apollographql.com/
[vue-apollo]: https://github.com/Akryum/vue-apollo/
[vue-apollo-docs]: https://akryum.github.io/vue-apollo/
[feature-flags]: ../feature_flags.md
[default-client]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/assets/javascripts/lib/graphql.js
[apollo-client-docs]: https://www.apollographql.com/docs/tutorial/client.html
[vue-test-utils]: https://vue-test-utils.vuejs.org/
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[apollo-link-state]: https://www.apollographql.com/docs/link/links/state.html