GraphQL

Getting Started

Helpful Resources

General resources:

• 📚 Official Introduction to GraphQL
• 📚 Official Introduction to Apollo

GraphQL at GitLab:

• 🎬 GitLab Unfiltered GraphQL playlist
• 🎬 GraphQL at GitLab: Deep Dive (video) by Nick Thomas
  • An overview of the history of GraphQL at GitLab (not frontend-specific)
• 🎬 GitLab Feature Walkthrough with GraphQL and Vue Apollo (video) by Natalia Tepluhina
  • A real-life example of implementing a frontend feature in GitLab using GraphQL
• 🎬 History of client-side GraphQL at GitLab (video) Illya Klymov and Natalia Tepluhina
• 🎬 From Vuex to Apollo (video) by Natalia Tepluhina
  • A useful overview of when Apollo might be a better choice than Vuex, and how one could go about the transition
• 🛠 Vuex -> Apollo Migration: a proof-of-concept project
  • A collection of examples that show the possible approaches for state management with Vue+GraphQL+(Vuex or Apollo) apps

Libraries

We use Apollo (specifically Apollo Client) and Vue Apollo when using GraphQL for frontend development.

If you are using GraphQL within a Vue application, the Usage in Vue section can help you learn how to integrate Vue Apollo.

For other use cases, check out the Usage outside of Vue section.

We use Immer for immutable cache updates; see Immutability and cache updates for more information.

Tooling

• Apollo Client Devtools

Apollo GraphQL VS Code extension

If you use VS Code, the Apollo GraphQL extension supports autocompletion in .graphql files. To set up the GraphQL extension, follow these steps:

1. Add an apollo.config.js file to the root of your gitlab local directory.

2. Populate the file with the following content:

   module.exports = {
     client: {
       includes: ['./app/assets/javascripts/**/*.graphql', './ee/app/assets/javascripts/**/*.graphql'],
       service: {
         name: 'GitLab',
         localSchemaFile: './doc/api/graphql/reference/gitlab_schema.graphql',
       },
     },
   };

3. Restart VS Code.

Exploring the GraphQL API

Our GraphQL API can be explored via GraphiQL at your instance's /-/graphql-explorer or at GitLab.com. Consult the GitLab GraphQL API Reference documentation where needed.

You can check all existing queries and mutations on the right side of GraphiQL in its Documentation explorer. It's also possible to write queries and mutations directly on the left tab and check their execution by clicking Execute query button on the top left:

Apollo Client

To save duplicated clients getting created in different apps, we have a default client that should be used. This sets up the Apollo client with the correct URL and also sets the CSRF headers.

Default client accepts two parameters: resolvers and config.

• resolvers parameter is created to accept an object of resolvers for local state management queries and mutations
• config parameter takes an object of configuration settings:
  • cacheConfig field accepts an optional object of settings to customize Apollo cache
  • baseUrl allows us to pass a URL for GraphQL endpoint different from our main endpoint (i.e.${gon.relative_url_root}/api/graphql)
  • assumeImmutableResults (set to false by default) - this setting, when set to true, will assume that every single operation on updating Apollo Cache is immutable. It also sets freezeResults to true, so any attempt on mutating Apollo Cache will throw a console warning in development environment. Please ensure you're following the immutability pattern on cache update operations before setting this option to true.
  • fetchPolicy determines how you want your component to interact with the Apollo cache. Defaults to "cache-first".

GraphQL Queries

To save query compilation at runtime, webpack can directly import .graphql files. This allows webpack to pre-process the query at compile time instead of the client doing compilation of queries.

To distinguish queries from mutations and fragments, the following naming convention is recommended:

• all_users.query.graphql for queries;
• add_user.mutation.graphql for mutations;
• basic_user.fragment.graphql for fragments.

Fragments

Fragments are a way to make your complex GraphQL queries more readable and re-usable. Here is an example of GraphQL fragment:

fragment DesignListItem on Design {
  id
  image
  event
  filename
  notesCount
}

Fragments can be stored in separate files, imported and used in queries, mutations, or other fragments.

#import "./design_list.fragment.graphql"
#import "./diff_refs.fragment.graphql"

fragment DesignItem on Design {
  ...DesignListItem
  fullPath
  diffRefs {
    ...DesignDiffRefs
  }
}

More about fragments: GraphQL Docs

Global IDs

The GitLab GraphQL API expresses id fields as Global IDs rather than the PostgreSQL primary key id. Global ID is a convention used for caching and fetching in client-side libraries.

To convert a Global ID to the primary key id, you can use getIdFromGraphQLId:

import { getIdFromGraphQLId } from '~/graphql_shared/utils';

const primaryKeyId = getIdFromGraphQLId(data.id);

Immutability and cache updates

From Apollo version 3.0.0 all the cache updates need to be immutable; it needs to be replaced entirely with a new and updated object.

To facilitate the process of updating the cache and returning the new object we use the library Immer. When possible, follow these conventions:

• The updated cache is named data.
• The original cache data is named sourceData.

A typical update process looks like this:

...
const sourceData = client.readQuery({ query });

const data = produce(sourceData, draftState => {
  draftState.commits.push(newCommit);
});

client.writeQuery({
  query,
  data,
});
...

As shown in the code example by using produce, we can perform any kind of direct manipulation of the draftState. Besides, immer guarantees that a new state which includes the changes to draftState will be generated.

Finally, to verify whether the immutable cache update is working properly, we need to change assumeImmutableResults to true in the default client configuration (see Apollo Client for more information).

If everything is working properly assumeImmutableResults should remain set to true.

Usage in Vue

To use Vue Apollo, import the Vue Apollo plugin as well as the default client. This should be created at the same point the Vue application is mounted.

import Vue from 'vue';
import VueApollo from 'vue-apollo';
import createDefaultClient from '~/lib/graphql';
Vue.use(VueApollo);

const apolloProvider = new VueApollo({
  defaultClient: createDefaultClient(),
});

new Vue({
  ...,
  apolloProvider,
  ...
});

Read more about Vue Apollo in the Vue Apollo documentation.

Local state with Apollo

It is possible to manage an application state with Apollo by passing 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.

import Vue from 'vue';
import VueApollo from 'vue-apollo';
import createDefaultClient from '~/lib/graphql';
Vue.use(VueApollo);

const defaultClient = createDefaultClient();

defaultClient.cache.writeData({
  data: {
    user: {
      name: 'John',
      surname: 'Doe',
      age: 30
    },
  },
});

const apolloProvider = new VueApollo({
  defaultClient,
});

We can query local data with @client Apollo directive:

// user.query.graphql

query User {
  user @client {
    name
    surname
    age
  }
}

Along with creating local data, we can also extend existing GraphQL types with @client fields. This is extremely useful when we need to mock an API responses for fields not yet added to our GraphQL API.

Mocking API response with local Apollo cache

Using local Apollo Cache is handy when we have a need to mock some GraphQL API responses, queries or mutations locally (e.g. when they're still not added to our actual API).

For example, we have a fragment on DesignVersion used in our queries:

fragment VersionListItem on DesignVersion {
  id
  sha
}

We need to fetch also version author and the 'created at' property to display them in the versions dropdown but these changes are still not implemented in our API. We can change the existing fragment to get a mocked response for these new fields:

fragment VersionListItem on DesignVersion {
  id
  sha
  author @client {
    avatarUrl
    name
  }
  createdAt @client
}

Now Apollo will try to find a resolver for every field marked with @client directive. Let's create a resolver for DesignVersion type (why DesignVersion? because our fragment was created on this type).

// resolvers.js

const resolvers = {
  DesignVersion: {
    author: () => ({
      avatarUrl:
        'https://www.gravatar.com/avatar/e64c7d89f26bd1972efa854d13d7dd61?s=80&d=identicon',
      name: 'Administrator',
      __typename: 'User',
    }),
    createdAt: () => '2019-11-13T16:08:11Z',
  },
};

export default resolvers;

We need to pass a resolvers object to our existing Apollo Client:

// graphql.js

import createDefaultClient from '~/lib/graphql';
import resolvers from './graphql/resolvers';

const defaultClient = createDefaultClient(resolvers);

For each attempt to fetch a version, our client will fetch id and sha from the remote API endpoint and will assign our hardcoded values to the author and createdAt version properties. With this data, frontend developers are able to work on their UI without being blocked by backend. When the actual response is added to the API, our custom local resolver can be removed and the only change to the query/fragment is to remove the @client directive.

Read more about local state management with Apollo in the Vue Apollo documentation.

Using with Vuex

When Apollo Client is used within Vuex and fetched data is stored in the Vuex store, there is no need to keep Apollo Client cache enabled. Otherwise we would have data from the API stored in two places - Vuex store and Apollo Client cache. With Apollo's default settings, a subsequent fetch from the GraphQL API could result in fetching data from Apollo cache (in the case where we have the same query and variables). To prevent this behavior, we need to disable Apollo Client cache by passing a valid fetchPolicy option to its constructor:

import fetchPolicies from '~/graphql_shared/fetch_policy_constants';

export const gqClient = createGqClient(
  {},
  {
    fetchPolicy: fetchPolicies.NO_CACHE,
  },
);

Feature flags in queries

Sometimes it may be useful to have an entity in the GraphQL query behind a feature flag. For example, when working on a feature where the backend has already been merged but the frontend hasn't you might want to put the GraphQL entity behind a feature flag to allow for smaller merge requests to be created and merged.

To do this we can use the @include directive to exclude an entity if the if statement passes.

query getAuthorData($authorNameEnabled: Boolean = false) {
  username
  name @include(if: $authorNameEnabled)
}

Then in the Vue (or JavaScript) call to the query we can pass in our feature flag. This feature flag will need to be already setup correctly. See the feature flag documentation for the correct way to do this.

export default {
  apollo: {
    user: {
      query: QUERY_IMPORT,
      variables() {
        return {
          authorNameEnabled: gon?.features?.authorNameEnabled,
        };
      },
    }
  },
};

Manually triggering queries

Queries on a component's apollo property are made automatically when the component is created. Some components instead want the network request made on-demand, for example a dropdown with lazy-loaded items.

There are two ways to do this:

1. Use the skip property

export default {
  apollo: {
    user: {
      query: QUERY_IMPORT,
      skip() {
        // only make the query when dropdown is open
        return !this.isOpen;
      },
    }
  },
};

1. Using addSmartQuery

You can manually create the Smart Query in your method.

handleClick() {
  this.$apollo.addSmartQuery('user', {
    // this takes the same values as you'd have in the `apollo` section
    query: QUERY_IMPORT,
  }),
};

Working with pagination

The GitLab GraphQL API uses Relay-style cursor pagination for connection types. This means a "cursor" is used to keep track of where in the data set the next items should be fetched from. GraphQL Ruby Connection Concepts is a good overview and introduction to connections.

Every connection type (for example, DesignConnection and DiscussionConnection) has a field pageInfo that contains an information required for pagination:

pageInfo {
  endCursor
  hasNextPage
  hasPreviousPage
  startCursor
}

Here:

• startCursor and endCursor display the cursor of the first and last items respectively.
• hasPreviousPage and hasNextPage allow us to check if there are more pages available before or after the current page.

When we fetch data with a connection type, we can pass cursor as after or before parameter, indicating a starting or ending point of our pagination. They should be followed with first or last parameter respectively to indicate how many items we want to fetch after or before a given endpoint.

For example, here we're fetching 10 designs after a cursor (let us call this projectQuery):

#import "~/graphql_shared/fragments/pageInfo.fragment.graphql"

query {
  project(fullPath: "root/my-project") {
    id
    issue(iid: "42") {
      designCollection {
        designs(atVersion: null, after: "Ihwffmde0i", first: 10) {
          edges {
            node {
              id
            }
          }
          pageInfo {
            ...PageInfo
          }
        }
      }
    }
  }
}

Note that we are using the pageInfo.fragment.graphql to populate the pageInfo information.

Using fetchMore method in components

This approach makes sense to use with user-handled pagination (e.g. when the scrolls to fetch more data or explicitly clicks a "Next Page"-button). When we need to fetch all the data initially, it is recommended to use a (non-smart) query, instead.

When making an initial fetch, we usually want to start a pagination from the beginning. In this case, we can either:

• Skip passing a cursor.
• Pass null explicitly to after.

After data is fetched, we can use the update-hook as an opportunity to customize the data that is set in the Vue component property, getting a hold of the pageInfo object among other data.

In the result-hook, we can inspect the pageInfo object to see if we need to fetch the next page. Note that we also keep a requestCount to ensure that the application does not keep requesting the next page, indefinitely:

data() {
  return {
    pageInfo: null,
    requestCount: 0,
  }
},
apollo: {
  designs: {
    query: projectQuery,
    variables() {
      return {
        // ... The rest of the design variables
        first: 10,
      };
    },
    update(data) {
      const { id = null, issue = {} } = data.project || {};
      const { edges = [], pageInfo } = issue.designCollection?.designs || {};

      return {
        id,
        edges,
        pageInfo,
      };
    },
    result() {
      const { pageInfo } = this.designs;

      // Increment the request count with each new result
      this.requestCount += 1;
      // Only fetch next page if we have more requests and there is a next page to fetch
      if (this.requestCount < MAX_REQUEST_COUNT && pageInfo?.hasNextPage) {
        this.fetchNextPage(pageInfo.endCursor);
      }
    },
  },
},

When we want to move to the next page, we use an Apollo fetchMore method, passing a new cursor (and, optionally, new variables) there. In the updateQuery hook, we have to return a result we want to see in the Apollo cache after fetching the next page. Immers produce-function can help us with the immutability here:

fetchNextPage(endCursor) {
  this.$apollo.queries.designs.fetchMore({
    variables: {
      // ... The rest of the design variables
      first: 10,
      after: endCursor,
    },
    updateQuery(previousResult, { fetchMoreResult }) {
      // Here we can implement the logic of adding new designs to existing ones
      // (for example, if we use infinite scroll) or replacing old result
      // with the new one if we use numbered pages

      const { designs: previousDesigns } = previousResult.project.issue.designCollection;
      const { designs: newDesigns } = fetchMoreResult.project.issue.designCollection

      return produce(previousResult, draftData => {
        // `produce` gives us a working copy, `draftData`, that we can modify
        // as we please and from it will produce the next immutable result for us
        draftData.project.issue.designCollection.designs = [...previousDesigns, ...newDesigns];
      });
    },
  });
}

Using a recursive query in components

When it is necessary to fetch all paginated data initially an Apollo query can do the trick for us. If we need to fetch the next page based on user interactions, it is recommend to use a smartQuery along with the fetchMore-hook.

When the query resolves we can update the component data and inspect the pageInfo object to see if we need to fetch the next page, i.e. call the method recursively.

Note that we also keep a requestCount to ensure that the application does not keep requesting the next page, indefinitely.

data() {
  return {
    requestCount: 0,
    isLoading: false,
    designs: {
      edges: [],
      pageInfo: null,
    },
  }
},
created() {
  this.fetchDesigns();
},
methods: {
  handleError(error) {
    this.isLoading = false;
    // Do something with `error`
  },
  fetchDesigns(endCursor) {
    this.isLoading = true;

    return this.$apollo
      .query({
        query: projectQuery,
        variables() {
          return {
            // ... The rest of the design variables
            first: 10,
            endCursor,
          };
        },
      })
      .then(({ data }) => {
        const { id = null, issue = {} } = data.project || {};
        const { edges = [], pageInfo } = issue.designCollection?.designs || {};

        // Update data
        this.designs = {
          id,
          edges: [...this.designs.edges, ...edges];
          pageInfo: pageInfo;
        };

        // Increment the request count with each new result
        this.requestCount += 1;
        // Only fetch next page if we have more requests and there is a next page to fetch
        if (this.requestCount < MAX_REQUEST_COUNT && pageInfo?.hasNextPage) {
          this.fetchDesigns(pageInfo.endCursor);
        } else {
          this.isLoading = false;
        }
      })
      .catch(this.handleError);
  },
},

Pagination and optimistic updates

When Apollo caches paginated data client-side, it includes pageInfo variables in the cache key. If you wanted to optimistically update that data, you'd have to provide pageInfo variables when interacting with the cache via .readQuery() or .writeQuery(). This can be tedious and counter-intuitive.

To make it easier to deal with cached paginated queries, Apollo provides the @connection directive. The directive accepts a key parameter that will be used as a static key when caching the data. You'd then be able to retrieve the data without providing any pagination-specific variables.

Here's an example of a query using the @connection directive:

#import "~/graphql_shared/fragments/pageInfo.fragment.graphql"

query DastSiteProfiles($fullPath: ID!, $after: String, $before: String, $first: Int, $last: Int) {
  project(fullPath: $fullPath) {
    siteProfiles: dastSiteProfiles(after: $after, before: $before, first: $first, last: $last)
      @connection(key: "dastSiteProfiles") {
      pageInfo {
        ...PageInfo
      }
      edges {
        cursor
        node {
          id
          # ...
        }
      }
    }
  }
}

In this example, Apollo will store the data with the stable dastSiteProfiles cache key.

To retrieve that data from the cache, you'd then only need to provide the $fullPath variable, omitting pagination-specific variables like after or before:

const data = store.readQuery({
  query: dastSiteProfilesQuery,
  variables: {
    fullPath: 'namespace/project',
  },
});

Read more about the @connection directive in Apollo's documentation.

Managing performance

The Apollo client will batch queries by default. This means that if you have 3 queries defined, Apollo will group them into one request, send the single request off to the server and only respond once all 3 queries have completed.

If you need to have queries sent as individual requests, additional context can be provided to tell Apollo to do this.

export default {
  apollo: {
    user: {
      query: QUERY_IMPORT,
      context: {
        isSingleRequest: true,
      }
    }
  },
};

Testing

Mocking response as component data

With 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

it('tests apollo component', () => {
  const vm = shallowMount(App);

  vm.setData({
    ...mockData
  });
});

Testing loading state

If we need to test how our component renders when results from the GraphQL API are still loading, we can mock a loading state into respective Apollo queries/mutations:

  function createComponent({
    loading = false,
  } = {}) {
    const $apollo = {
      queries: {
        designs: {
          loading,
        },
      },
    };

    wrapper = shallowMount(Index, {
      sync: false,
      mocks: { $apollo }
    });
  }

  it('renders loading icon', () => {
  createComponent({ loading: true });

  expect(wrapper.element).toMatchSnapshot();
})

Testing Apollo components

If we use ApolloQuery or ApolloMutation in our components, in order to test their functionality we need to add a stub first:

import { ApolloMutation } from 'vue-apollo';

function createComponent(props = {}) {
  wrapper = shallowMount(MyComponent, {
    sync: false,
    propsData: {
      ...props,
    },
    stubs: {
      ApolloMutation,
    },
  });
}

ApolloMutation component exposes mutate method via scoped slot. If we want to test this method, we need to add it to mocks:

const mutate = jest.fn().mockResolvedValue();
const $apollo = {
  mutate,
};

function createComponent(props = {}) {
  wrapper = shallowMount(MyComponent, {
    sync: false,
    propsData: {
      ...props,
    },
    stubs: {
      ApolloMutation,
    },
    mocks: {
      $apollo,
    }
  });
}

Then we can check if mutate is called with correct variables:

const mutationVariables = {
  mutation: createNoteMutation,
  update: expect.anything(),
  variables: {
    input: {
      noteableId: 'noteable-id',
      body: 'test',
      discussionId: '0',
    },
  },
};

it('calls mutation on submitting form ', () => {
  createComponent()
  findReplyForm().vm.$emit('submitForm');

  expect(mutate).toHaveBeenCalledWith(mutationVariables);
});

Testing with mocked Apollo Client

To test the logic of Apollo cache updates, we might want to mock an Apollo Client in our unit tests. We use mock-apollo-client library to mock Apollo client and createMockApollo helper we created on top of it.

To separate tests with mocked client from 'usual' unit tests, it's recommended to create an additional factory and pass the created mockApollo as an option to the createComponent-factory. This way we only create Apollo Client instance when it's necessary.

We need to inject VueApollo to the Vue local instance and, likewise, it is recommended to call localVue.use() within createMockApolloProvider() to only load it when it is necessary.

import VueApollo from 'vue-apollo';
import { createLocalVue } from '@vue/test-utils';

const localVue = createLocalVue();

function createMockApolloProvider() {
  localVue.use(VueApollo);

  return createMockApollo(requestHandlers);
}

function createComponent(options = {}) {
  const { mockApollo } = options;
  ...
  return shallowMount(..., {
    localVue,
    apolloProvider: mockApollo,
    ...
  });
}

After this, you can control whether you need a variable for mockApollo and assign it in the appropriate describe-scope:

describe('Some component', () => {
  let wrapper;

  describe('with Apollo mock', () => {
    let mockApollo;

    beforeEach(() => {
      mockApollo = createMockApolloProvider();
      wrapper = createComponent({ mockApollo });
    });
  });
});

Within createMockApolloProvider-factory, we need to define an array of handlers for every query or mutation:

import getDesignListQuery from '~/design_management/graphql/queries/get_design_list.query.graphql';
import permissionsQuery from '~/design_management/graphql/queries/design_permissions.query.graphql';
import moveDesignMutation from '~/design_management/graphql/mutations/move_design.mutation.graphql';

describe('Some component with Apollo mock', () => {
  let wrapper;
  let mockApollo;

  function createMockApolloProvider() {
    Vue.use(VueApollo);

    const requestHandlers = [
      [getDesignListQuery, jest.fn().mockResolvedValue(designListQueryResponse)],
      [permissionsQuery, jest.fn().mockResolvedValue(permissionsQueryResponse)],
    ];
    ...
  }
})

After this, we need to create a mock Apollo Client instance using a helper:

import createMockApollo from 'helpers/mock_apollo_helper';

describe('Some component', () => {
  let wrapper;

  function createMockApolloProvider() {
    Vue.use(VueApollo);

    const requestHandlers = [
      [getDesignListQuery, jest.fn().mockResolvedValue(designListQueryResponse)],
      [permissionsQuery, jest.fn().mockResolvedValue(permissionsQueryResponse)],
    ];

    return createMockApollo(requestHandlers);
  }

  function createComponent(options = {}) {
    const { mockApollo } = options;

    return shallowMount(Index, {
      localVue,
      apolloProvider: mockApollo,
    });
  }

  describe('with Apollo mock', () => {
    let mockApollo;

    beforeEach(() => {
      mockApollo = createMockApolloProvider();
      wrapper = createComponent({ mockApollo });
    });
  });
});

When mocking resolved values, ensure the structure of the response is the same as the actual API response. For example, root property should be data.

When testing queries, please keep in mind they are promises, so they need to be resolved to render a result. Without resolving, we can check the loading state of the query:

it('renders a loading state', () => {
  const mockApollo = createMockApolloProvider();
  const wrapper = createComponent({ mockApollo });

  expect(wrapper.find(LoadingSpinner).exists()).toBe(true)
});

it('renders designs list', async () => {
  const mockApollo = createMockApolloProvider();
  const wrapper = createComponent({ mockApollo });

  jest.runOnlyPendingTimers();
  await wrapper.vm.$nextTick();

  expect(findDesigns()).toHaveLength(3);
});

If we need to test a query error, we need to mock a rejected value as request handler:

function createMockApolloProvider() {
  ...
  const requestHandlers = [
    [getDesignListQuery, jest.fn().mockRejectedValue(new Error('GraphQL error')],
  ];
  ...
}
...

it('renders error if query fails', async () => {
  const wrapper = createComponent();

  jest.runOnlyPendingTimers();
  await wrapper.vm.$nextTick();

  expect(wrapper.find('.test-error').exists()).toBe(true)
})

Request handlers can also be passed to component factory as a parameter.

Mutations could be tested the same way with a few additional nextTicks to get the updated result:

function createMockApolloProvider({
  moveHandler = jest.fn().mockResolvedValue(moveDesignMutationResponse),
}) {
  Vue.use(VueApollo);

  moveDesignHandler = moveHandler;

  const requestHandlers = [
    [getDesignListQuery, jest.fn().mockResolvedValue(designListQueryResponse)],
    [permissionsQuery, jest.fn().mockResolvedValue(permissionsQueryResponse)],
    [moveDesignMutation, moveDesignHandler],
  ];

  return createMockApollo(requestHandlers);
}

function createComponent(options = {}) {
  const { mockApollo } = options;

  return shallowMount(Index, {
    localVue,
    apolloProvider: mockApollo,
  });
}
...
it('calls a mutation with correct parameters and reorders designs', async () => {
  const mockApollo = createMockApolloProvider({});
  const wrapper = createComponent({ mockApollo });

  wrapper.find(VueDraggable).vm.$emit('change', {
    moved: {
      newIndex: 0,
      element: designToMove,
    },
  });

  expect(moveDesignHandler).toHaveBeenCalled();

  await wrapper.vm.$nextTick();

  expect(
    findDesigns()
      .at(0)
      .props('id'),
  ).toBe('2');
});

Testing @client queries

Using mock resolvers

If your application contains @client queries, you get the following Apollo Client warning when passing only handlers:

Unexpected call of console.warn() with:
Warning: mock-apollo-client - The query is entirely client-side (using @client directives) and resolvers have been configured. The request handler will not be called.

To fix this you should define mock resolvers instead of mock handlers. For example, given the following @client query:

query getBlobContent($path: String, $ref: String!) {
  blobContent(path: $path, ref: $ref) @client {
    rawData
  }
}

And its actual client-side resolvers:

import Api from '~/api';

export const resolvers = {
  Query: {
    blobContent(_, { path, ref }) {
      return {
        __typename: 'BlobContent',
        rawData: Api.getRawFile(path, { ref }).then(({ data }) => {
          return data;
        }),
      };
    },
  },
};

export default resolvers;

We can use a mock resolver that returns data with the same shape, while mock the result with a mock function:

let mockApollo;
let mockBlobContentData; // mock function, jest.fn();

const mockResolvers = {
  Query: {
    blobContent() {
      return {
        __typename: 'BlobContent',
        rawData: mockBlobContentData(), // the mock function can resolve mock data
      };
    },
  },
};

const createComponentWithApollo = ({ props = {} } = {}) => {
  mockApollo = createMockApollo([], mockResolvers); // resolvers are the second parameter

  wrapper = shallowMount(MyComponent, {
    localVue,
    propsData: {},
    apolloProvider: mockApollo,
    // ...
  })
};

After which, you can resolve or reject the value needed.

beforeEach(() => {
  mockBlobContentData = jest.fn();
});

it('shows data', async() => {
  mockBlobContentData.mockResolvedValue(data); // you may resolve or reject to mock the result

  createComponentWithApollo();

  await waitForPromises(); // wait on the resolver mock to execute

  expect(findContent().text()).toBe(mockCiYml);
});

Using cache.writeQuery

Sometimes we want to test a result hook of the local query. In order to have it triggered, we need to populate a cache with correct data to be fetched with this query:

query fetchLocalUser {
  fetchLocalUser @client {
    name
  }
}

import fetchLocalUserQuery from '~/design_management/graphql/queries/fetch_local_user.query.graphql';

function createMockApolloProvider() {
  Vue.use(VueApollo);

  const requestHandlers = [
    [getDesignListQuery, jest.fn().mockResolvedValue(designListQueryResponse)],
    [permissionsQuery, jest.fn().mockResolvedValue(permissionsQueryResponse)],
  ];

  const mockApollo = createMockApollo(requestHandlers, {});
  mockApollo.clients.defaultClient.cache.writeQuery({
    query: fetchLocalUserQuery,
    data: {
      fetchLocalUser: {
        __typename: 'User',
        name: 'Test',
      },
    },
  });

  return mockApollo;
}

function createComponent(options = {}) {
  const { mockApollo } = options;

  return shallowMount(Index, {
    localVue,
    apolloProvider: mockApollo,
  });
}

Sometimes it is necessary to control what the local resolver returns and inspect how it is called by the component. This can be done by mocking your local resolver:

import fetchLocalUserQuery from '~/design_management/graphql/queries/fetch_local_user.query.graphql';

function createMockApolloProvider(options = {}) {
  Vue.use(VueApollo);
  const { fetchLocalUserSpy } = options;

  const mockApollo = createMockApollo([], {
    Query: {
      fetchLocalUser: fetchLocalUserSpy,
    },
  });

  // Necessary for local resolvers to be activated
  mockApollo.clients.defaultClient.cache.writeQuery({
    query: fetchLocalUserQuery,
    data: {},
  });

  return mockApollo;
}

In the test you can then control what the spy is supposed to do and inspect the component after the request have returned:

describe('My Index test with `createMockApollo`', () => {
  let wrapper;
  let fetchLocalUserSpy;

  afterEach(() => {
    wrapper.destroy();
    wrapper = null;
    fetchLocalUserSpy = null;
  });

  describe('when loading', () => {
    beforeEach(() => {
      const mockApollo = createMockApolloProvider();
      wrapper = createComponent({ mockApollo });
    });

    it('displays the loader', () => {
      // Assess that the loader is present
    });
  });

  describe('with data', () => {
    beforeEach(async () => {
      fetchLocalUserSpy = jest.fn().mockResolvedValue(localUserQueryResponse);
      const mockApollo = createMockApolloProvider(fetchLocalUserSpy);
      wrapper = createComponent({ mockApollo });
      await waitForPromises();
    });

    it('should fetch data once', () => {
      expect(fetchLocalUserSpy).toHaveBeenCalledTimes(1);
    });

    it('displays data', () => {
      // Assess that data is present
    });
  });

  describe('with error', () => {
    const error = 'Error!';

    beforeEach(async () => {
      fetchLocalUserSpy = jest.fn().mockRejectedValueOnce(error);
      const mockApollo = createMockApolloProvider(fetchLocalUserSpy);
      wrapper = createComponent({ mockApollo });
      await waitForPromises();
    });

    it('should fetch data once', () => {
      expect(fetchLocalUserSpy).toHaveBeenCalledTimes(1);
    });

    it('displays the error', () => {
      // Assess that the error is displayed
    });
  });
});

Handling errors

The GitLab GraphQL mutations currently have two distinct error modes: Top-level and errors-as-data.

When utilising a GraphQL mutation, we must consider handling both of these error modes to ensure that the user receives the appropriate feedback when an error occurs.

Top-level errors

These errors are located at the "top level" of a GraphQL response. These are non-recoverable errors including argument errors and syntax errors, and should not be presented directly to the user.

Handling top-level errors

Apollo is aware of top-level errors, so we are able to leverage Apollo's various error-handling mechanisms to handle these errors (e.g. handling Promise rejections after invoking the mutate method, or handling the error event emitted from the ApolloMutation component).

Because these errors are not intended for users, error messages for top-level errors should be defined client-side.

Errors-as-data

These errors are nested within the data object of a GraphQL response. These are recoverable errors that, ideally, can be presented directly to the user.

Handling errors-as-data

First, we must add errors to our mutation object:

mutation createNoteMutation($input: String!) {
  createNoteMutation(input: $input) {
    note {
      id
+     errors
    }
  }

Now, when we commit this mutation and errors occur, the response will include errors for us to handle:

{
  data: {
    mutationName: {
      errors: ["Sorry, we were not able to update the note."]
    }
  }
}

When handling errors-as-data, use your best judgement to determine whether to present the error message in the response, or another message defined client-side, to the user.

Usage outside of Vue

It is also possible to use GraphQL outside of Vue by directly importing and using the default client with queries.

import createDefaultClient from '~/lib/graphql';
import query from './query.graphql';

const defaultClient = createDefaultClient();

defaultClient.query({ query })
  .then(result => console.log(result));

When using Vuex, disable the cache when:

• The data is being cached elsewhere
• The use case does not need caching if the data is being cached elsewhere, or if there is simply no need for it for the given use case.

import createDefaultClient from '~/lib/graphql';
import fetchPolicies from '~/graphql_shared/fetch_policy_constants';

const defaultClient = createDefaultClient(
  {},
  {
    fetchPolicy: fetchPolicies.NO_CACHE,
  },
);

Making initial queries early with GraphQL startup calls

To improve performance, sometimes we want to make initial GraphQL queries early. In order to do this, we can add them to startup calls with the following steps:

• Move all the queries you need initially in your application to app/graphql/queries;

• Add __typename property to every nested query level:

  query getPermissions($projectPath: ID!) {
    project(fullPath: $projectPath) {
      __typename
      userPermissions {
        __typename
        pushCode
        forkProject
        createMergeRequestIn
      }
    }
  }

• If queries contain fragments, you need to move fragments to the query file directly instead of importing them:

  fragment PageInfo on PageInfo {
    __typename
    hasNextPage
    hasPreviousPage
    startCursor
    endCursor
  }
  
  query getFiles(
    $projectPath: ID!
    $path: String
    $ref: String!
  ) {
    project(fullPath: $projectPath) {
      __typename
      repository {
        __typename
        tree(path: $path, ref: $ref) {
          __typename
            pageInfo {
              ...PageInfo
            }
          }
        }
      }
    }
  }

• If the fragment is used only once, we can also remove the fragment altogether:

  query getFiles(
    $projectPath: ID!
    $path: String
    $ref: String!
  ) {
    project(fullPath: $projectPath) {
      __typename
      repository {
        __typename
        tree(path: $path, ref: $ref) {
          __typename
            pageInfo {
              __typename
              hasNextPage
              hasPreviousPage
              startCursor
              endCursor
            }
          }
        }
      }
    }
  }

• Add startup call(s) with correct variables to the HAML file that serves as a view for your application. To add GraphQL startup calls, we use add_page_startup_graphql_call helper where the first parameter is a path to the query, the second one is an object containing query variables. Path to the query is relative to app/graphql/queries folder: for example, if we need a app/graphql/queries/repository/files.query.graphql query, the path will be repository/files.

  - current_route_path = request.fullpath.match(/-\/tree\/[^\/]+\/(.+$)/).to_a[1]
  - add_page_startup_graphql_call('repository/path_last_commit', { projectPath: @project.full_path, ref: current_ref, path: current_route_path || "" })
  - add_page_startup_graphql_call('repository/permissions', { projectPath: @project.full_path })
  - add_page_startup_graphql_call('repository/files', { nextPageCursor: "", pageSize: 100, projectPath: @project.full_path, ref: current_ref, path: current_route_path || "/"})