graphql-flutter

GraphQL Flutter

Flutter Widgets wrapper around graphql API

Project Homepage

Introduction

graphql_flutter provides an idiomatic flutter API and widgets for graphql/client.dart. They are co-developed on github, where you can find more in-depth examples. We also have a lively community on discord.

This guide is mostly focused on setup, widgets, and flutter-specific considerations. For more in-depth details on the graphql API, see the graphql README

• GraphQL Flutter
  • Installation
  • Migration Guide
  • Usage
    • GraphQL Provider
    • Query
      • Fetch More (Pagination)
    • Mutations
      • Optimism
    • Subscriptions
    • GraphQL Consumer
    • Other hooks
  • Code generation

Useful sections in the graphql README:

• in-depth link guide
• Direct Cache Access
• Cache Write Strictness
• Policies
• Exceptions
• AWS AppSync Support
• GraphQL Upload
• Parsing ASTs at build-time

Useful API Docs:

• GraphQLCache
• GraphQLDataProxy API docs (direct cache access)

Installation

First, depend on this package:

$ flutter pub add graphql_flutter

And then import it inside your dart code:

import 'package:graphql_flutter/graphql_flutter.dart';

Migration Guide

Find the migration from version 3 to version 4 here.

Usage

To connect to a GraphQL Server, we first need to create a GraphQLClient. A GraphQLClient requires both a cache and a link to be initialized.

In our example below, we will be using the Github Public API. we are going to use HttpLink which we will concatenate with AuthLink so as to attach our github access token. For the cache, we are going to use GraphQLCache.

...

import 'package:graphql_flutter/graphql_flutter.dart';

void main() async {

  // We're using HiveStore for persistence,
  // so we need to initialize Hive.
  await initHiveForFlutter();

  final HttpLink httpLink = HttpLink(
    'https://api.github.com/graphql',
  );

  final AuthLink authLink = AuthLink(
    getToken: () async => 'Bearer <YOUR_PERSONAL_ACCESS_TOKEN>',
    // OR
    // getToken: () => 'Bearer <YOUR_PERSONAL_ACCESS_TOKEN>',
  );

  final Link link = authLink.concat(httpLink);

  ValueNotifier<GraphQLClient> client = ValueNotifier(
    GraphQLClient(
      link: link,
      // The default store is the InMemoryStore, which does NOT persist to disk
      cache: GraphQLCache(store: HiveStore()),
    ),
  );

  ...
}

...

GraphQL Provider

In order to use the client, your Query and Mutation widgets must be wrapped with the GraphQLProvider widget.

We recommend wrapping your MaterialApp with the GraphQLProvider widget.

  ...

  return GraphQLProvider(
    client: client,
    child: MaterialApp(
      title: 'Flutter Demo',
      ...
    ),
  );

  ...

Query

Creating a query is as simple as creating a multiline string:

String readRepositories = """
  query ReadRepositories(\$nRepositories: Int!) {
    viewer {
      repositories(last: \$nRepositories) {
        nodes {
          id
          name
          viewerHasStarred
        }
      }
    }
  }
""";

In your widget:

// ...
Query(
  options: QueryOptions(
    document: gql(readRepositories), // this is the query string you just created
    variables: {
      'nRepositories': 50,
    },
    pollInterval: const Duration(seconds: 10),
  ),
  // Just like in apollo refetch() could be used to manually trigger a refetch
  // while fetchMore() can be used for pagination purpose
  builder: (QueryResult result, { VoidCallback? refetch, FetchMore? fetchMore }) {
    if (result.hasException) {
        return Text(result.exception.toString());
    }

    if (result.isLoading) {
      return const Text('Loading');
    }

    List? repositories = result.data?['viewer']?['repositories']?['nodes'];

    if (repositories == null) {
      return const Text('No repositories');
    }

    return ListView.builder(
      itemCount: repositories.length,
      itemBuilder: (context, index) {
        final repository = repositories[index];

        return Text(repository['name'] ?? '');
    });
  },
);
// ...

or if you prefer to use flutter-hooks, you can write the above as:

// ...
final readRespositoriesResult = useQuery(
  QueryOptions(
    document: gql(readRepositories), // this is the query string you just created
    variables: {
      'nRepositories': 50,
    },
    pollInterval: const Duration(seconds: 10),
  ),
);
final result = readRespositoriesResult.result;

if (result.hasException) {
    return Text(result.exception.toString());
}

if (result.isLoading) {
  return const Text('Loading');
}

List? repositories = result.data?['viewer']?['repositories']?['nodes'];

if (repositories == null) {
  return const Text('No repositories');
}

return ListView.builder(
  itemCount: repositories.length,
  itemBuilder: (context, index) {
    final repository = repositories[index];

    return Text(repository['name'] ?? '');
});
// ...

Fetch More (Pagination)

You can use fetchMore() function inside Query Builder to perform pagination. The fetchMore() function allows you to run an entirely new GraphQL operation and merge the new results with the original results. On top of that, you can re-use aspects of the Original query i.e. the Query or some of the Variables.

In order to use the FetchMore() function, you will need to first define FetchMoreOptions variable for the new query.

...
// this is returned by the GitHubs GraphQL API for pagination purpose
final Map pageInfo = result.data['search']['pageInfo'];
final String fetchMoreCursor = pageInfo['endCursor'];

/// **NOTE**: with the addition of strict data structure checking in v4,
/// it is easy to make mistakes in writing [updateQuery].
///
/// To mitigate this, [FetchMoreOptions.partial] has been provided.
FetchMoreOptions opts = FetchMoreOptions(
  variables: {'cursor': fetchMoreCursor},
  updateQuery: (previousResultData, fetchMoreResultData) {
    // this function will be called so as to combine both the original and fetchMore results
    // it allows you to combine them as you would like
    final List<dynamic> repos = [
      ...previousResultData['search']['nodes'] as List<dynamic>,
      ...fetchMoreResultData['search']['nodes'] as List<dynamic>
    ];

    // to avoid a lot of work, lets just update the list of repos in returned
    // data with new data, this also ensures we have the endCursor already set
    // correctly
    fetchMoreResultData['search']['nodes'] = repos;

    return fetchMoreResultData;
  },
);

...

And then, call the fetchMore() function and pass the FetchMoreOptions variable you defined above.

RaisedButton(
  child: Row(
    mainAxisAlignment: MainAxisAlignment.center,
    children: <Widget>[
      Text("Load More"),
    ],
  ),
  onPressed: () {
    fetchMore(opts);
  },
)

Mutations

Again first create a mutation string:

String addStar = """
  mutation AddStar(\$starrableId: ID!) {
    addStar(input: {starrableId: \$starrableId}) {
      starrable {
        viewerHasStarred
      }
    }
  }
""";

The syntax for mutations is fairly similar to that of a query. The only difference is that the first argument of the builder function is a mutation function. Just call it to trigger the mutations (Yeah we deliberately stole this from react-apollo.)

...

Mutation(
  options: MutationOptions(
    document: gql(addStar), // this is the mutation string you just created
    // you can update the cache based on results
    update: (GraphQLDataProxy cache, QueryResult result) {
      return cache;
    },
    // or do something with the result.data on completion
    onCompleted: (dynamic resultData) {
      print(resultData);
    },
  ),
  builder: (
    RunMutation runMutation,
    QueryResult result,
  ) {
    return FloatingActionButton(
      onPressed: () => runMutation({
        'starrableId': <A_STARTABLE_REPOSITORY_ID>,
      }),
      tooltip: 'Star',
      child: Icon(Icons.star),
    );
  },
);

...

The corresponding hook is

// ...

final addStarMutation = useMutation(
  MutationOptions(
    document: gql(addStar), // this is the mutation string you just created
    // you can update the cache based on results
    update: (GraphQLDataProxy cache, QueryResult result) {
      return cache;
    },
    // or do something with the result.data on completion
    onCompleted: (dynamic resultData) {
      print(resultData);
    },
  ),
);
return FloatingActionButton(
  onPressed: () => addStarMutation.runMutation({
    'starrableId': <A_STARTABLE_REPOSITORY_ID>,
  }),
  tooltip: 'Star',
  child: Icon(Icons.star),
);

// ...

graphql also provides file upload support as well.

Optimism

GraphQLCache allows for optimistic mutations by passing an optimisticResult to RunMutation. It will then call update(GraphQLDataProxy cache, QueryResult result) twice (once eagerly with optimisticResult), and rebroadcast all queries with the optimistic cache state.

A complete and well-commented rundown of how exactly one interfaces with the proxy provided to update can be fount in the GraphQLDataProxy API docs

...
FlutterWidget(
  onTap: () {
    toggleStar(
      { 'starrableId': repository['id'] },
      optimisticResult: {
        'action': {
          'starrable': {'viewerHasStarred': !starred}
        }
      },
    );
  },
)
...

With a bit more context (taken from the complete mutation example StarrableRepository):

// final Map<String, Object> repository;
// final bool optimistic;
// Map<String, Object> extractRepositoryData(Map<String, Object> data);
// Map<String, dynamic> get expectedResult;
Mutation(
  options: MutationOptions(
    document: gql(starred ? mutations.removeStar : mutations.addStar),
    update: (cache, result) {
      if (result.hasException) {
        print(result.exception);
      } else {
        final updated = {
          ...repository,
          ...extractRepositoryData(result.data),
        };
        cache.writeFragment(
          Fragment(
              document: gql(
            '''
              fragment fields on Repository {
                id
                name
                viewerHasStarred
              }
            ''',
            // helper for constructing FragmentRequest
          )).asRequest(idFields: {
            '__typename': updated['__typename'],
            'id': updated['id'],
          }),
          data: updated,
          broadcast: false,
        );
      }
    },
    onError: (OperationException error) { },
    onCompleted: (dynamic resultData) { },
  ),
  builder: (RunMutation toggleStar, QueryResult result) {
    return ListTile(
      leading: starred
          ? const Icon(
              Icons.star,
              color: Colors.amber,
            )
          : const Icon(Icons.star_border),
      trailing: result.isLoading || optimistic
          ? const CircularProgressIndicator()
          : null,
      title: Text(repository['name'] as String),
      onTap: () {
        toggleStar(
          {'starrableId': repository['id']},
          optimisticResult: expectedResult,
        );
      },
    );
  },
)

Subscriptions

The syntax for subscriptions is again similar to a query, however, it utilizes WebSockets and dart Streams to provide real-time updates from a server.

To use subscriptions, a subscription-consuming link must be split from your HttpLink or other terminating link route:

link = Link.split((request) => request.isSubscription, websocketLink, link);

Then you can subscribe to any subscriptions provided by your server schema:

final subscriptionDocument = gql(
  r'''
    subscription reviewAdded {
      reviewAdded {
        stars, commentary, episode
      }
    }
  ''',
);

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Subscription(
          options: SubscriptionOptions(
            document: subscriptionDocument,
          ),
          builder: (result) {
            if (result.hasException) {
              return Text(result.exception.toString());
            }

            if (result.isLoading) {
              return Center(
                child: const CircularProgressIndicator(),
              );
            }
            // ResultAccumulator is a provided helper widget for collating subscription results.
            // careful though! It is stateful and will discard your results if the state is disposed
            return ResultAccumulator.appendUniqueEntries(
              latest: result.data,
              builder: (context, {results}) => DisplayReviews(
                reviews: results.reversed.toList(),
              ),
            );
          }
        ),
      )
    );
  }
}

the corresponding implementation with hooks is:

final subscriptionDocument = gql(
  r'''
    subscription reviewAdded {
      reviewAdded {
        stars, commentary, episode
      }
    }
  ''',
);

class MyHomePage extends HooksWidget {
  @override
  Widget build(BuildContext context) {
    final result = useSubscription(
      SubscriptionOptions(
        document: subscriptionDocument,
      ),
    );
    
    Widget child;
    if (result.hasException) {
      child = Text(result.exception.toString());
    } else if (result.isLoading) {
      child = Center(
        child: const CircularProgressIndicator(),
      );
    } else {
      child = ResultAccumulator.appendUniqueEntries(
        latest: result.data,
        builder: (context, {results}) => DisplayReviews(
          reviews: results.reversed.toList(),
        ),
      );    
    }
    return Scaffold(
      body: Center(child: child)
    );
  }
}

Other hooks

Besides useMutation, useQuery, and useSubscription, this package contains the following hooks:

final client = useGraphQLClient(); // Fetch the current client
final observableQuery = useWatchQuery(WatchQueryOptions(...)); // Watch a query
final mutationObservableQuery = useWatchMutation(WatchQueryOptions(...)); // Watch a query

GraphQL Consumer

If you want to use the client directly, say for some its direct cache update methods, You can use GraphQLConsumer to grab it from any context descended from a GraphQLProvider:

  ...

  return GraphQLConsumer(
    builder: (GraphQLClient client) {
      // do something with the client

      return Container(
        child: Text('Hello world'),
      );
    },
  );

  ...

## Code generation

This package does not support code-generation out of the box, but graphql_codegen does!

This package generate hooks and options which takes away the struggle of serialization and gives you confidence through type-safety.

For example, by creating the .graphql file

  query ReadRepositories($nRepositories: Int!) {
    viewer {
      repositories(last: $nRepositories) {
        nodes {
          id
          name
        }
      }
    }
  }

after building, you’ll be able to query this in your code through the hook:

final queryResult = useQueryReadRepositories(
  OptionsQueryReadRepositories(
    variables: VariablesQueryReadRepositories(
      nRepositories: 10
    )
  )
);
if (queryResult.result.hasException) {
  return Text(result.exception.toString());
}
if (queryResult.result.isLoading) {
  return Text(text: "LOADING");
}
final data = queryResult.result.parsedData;

return Column(
  children: data?.viewer.repositores.nodes.map((node) => Text(text: node.name));
);

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