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client.dart
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client.dart
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import 'package:meta/meta.dart';
import 'dart:async';
import 'package:gql/ast.dart';
import 'package:gql_link/gql_link.dart';
import 'package:gql_exec/gql_exec.dart';
import 'package:rxdart/rxdart.dart';
import './query_response.dart';
import './query_request.dart';
import '../cache/cache.dart';
import './fetch_policy.dart';
import '../helpers/operation_type.dart';
import '../cache/options.dart';
import '../cache/cache_proxy.dart';
import './client_options.dart';
class GQLClient {
final Link link;
final GQLCache cache;
final GQLClientOptions options;
/// Keeps track of network connection status. For offline mutations to work,
/// you must update this value when the network status changes.
// TODO: implement offline mutation cache
final isConnected = BehaviorSubject<bool>.seeded(true);
/// Add a [QueryRequest] to the controller, then create a [responseStream]
/// with the same [QueryRequest] to listen for [QueryResponse]s.
final queryController = StreamController<QueryRequest>.broadcast();
GQLClient({
@required this.link,
GQLCache cache,
GQLClientOptions options,
}) : options = options ?? GQLClientOptions(),
cache = cache ?? GQLCache();
Stream<QueryResponse<T>> responseStream<T>(QueryRequest<T> request) {
bool initial = true;
return queryController.stream
// Filter for only the relevent queries
.whereType<QueryRequest<T>>()
.where((req) => req.queryId == request.queryId)
// (if enabled) recursively add __typename field to every node in query
.map(_addTypename)
// Fetch [QueryResponse] from network (and optionally cache results)
// or fetch from cache, depending on the [FetchPolicy]. Switches to
// the latest stream for a given [queryId].
.switchMap((req) => _responseStream(req))
// Update the result based on previous result for the given [queryId],
// if applicable. This enables features like pagination.
.transform(StreamTransformer.fromBind(_updateResultStream))
// Trigger the [QueryRequest] on first listen
.doOnListen(
() async {
if (initial) {
await Future.delayed(Duration.zero);
queryController.add(request);
}
initial = false;
},
);
}
/// Optionally adds [__typename] to each node of the operation
QueryRequest<T> _addTypename<T>(QueryRequest<T> request) {
if (!options.addTypename) return request;
final document = transform(
request.operation.document,
[AddTypenameVisitor()],
);
return request
..operation = Operation(
document: document,
operationName: request.operation.operationName,
);
}
/// Determines how to resolve a query based on the [FetchPolicy] and caches
/// responses from the network if required by the policy.
Stream<QueryResponse<T>> _responseStream<T>(QueryRequest<T> queryRequest) {
final fetchPolicy = queryRequest.fetchPolicy ??
options.defaultFetchPolicies[operationType(queryRequest)];
switch (fetchPolicy) {
case FetchPolicy.NoCache:
return _optimisticNetworkResponseStream(queryRequest);
case FetchPolicy.NetworkOnly:
return _optimisticNetworkResponseStream(queryRequest)
.doOnData(_writeToCache)
.doOnData(_runUpdateCacheHandlers);
case FetchPolicy.CacheOnly:
return _cacheResponseStream(queryRequest)
.doOnData(_runUpdateCacheHandlers);
case FetchPolicy.CacheFirst:
return _cacheResponseStream(queryRequest).take(1).switchMap(
(result) => result.data != null
? _cacheResponseStream(queryRequest)
.doOnData(_runUpdateCacheHandlers)
: _optimisticNetworkResponseStream(queryRequest)
.doOnData(_writeToCache)
.doOnData(_runUpdateCacheHandlers)
.switchMap((_) => _cacheResponseStream(queryRequest)),
);
case FetchPolicy.CacheAndNetwork:
{
final responseStreamFromNetwork =
_optimisticNetworkResponseStream(queryRequest).shareValue();
return _cacheResponseStream(queryRequest)
.doOnData(_runUpdateCacheHandlers)
.where((response) => response.data != null)
.takeUntil(responseStreamFromNetwork)
.concatWith([
responseStreamFromNetwork
.doOnData(_writeToCache)
.switchMap((_) => _cacheResponseStream(queryRequest))
]);
}
}
}
/// Creates a response stream, starting with an optimistic [QueryResponse]
/// if a [QueryRequest.optimisticResponse] is proviced, then remmoves the
/// optimistic patch from the cache once the network response is received.
Stream<QueryResponse<T>> _optimisticNetworkResponseStream<T>(
QueryRequest<T> queryRequest) =>
queryRequest.optimisticResponse == null
? _networkResponseStream(queryRequest)
: _networkResponseStream(queryRequest)
.startWith(
QueryResponse(
queryRequest: queryRequest,
data: queryRequest.parseData(queryRequest.optimisticResponse),
optimistic: true),
)
.doOnData(
(response) {
if (response.optimistic == false)
cache.removeOptimisticPatch(response.queryRequest.queryId);
},
);
/// Fetches the query from the network, mapping the result to a
/// [QueryResponse].
Stream<QueryResponse<T>> _networkResponseStream<T>(
QueryRequest<T> queryRequest) =>
link
.request(
Request(
operation: Operation(
document: queryRequest.operation.document,
operationName: queryRequest.operation.operationName),
variables: queryRequest.variables),
)
.map(
(response) => QueryResponse(
queryRequest: queryRequest,
data: (response.data == null || response.data.isEmpty)
? null
: queryRequest.parseData(response.data),
errors: response.errors,
),
);
/// Fetches the query from the cache, mapping the result to a
/// [QueryResponse].
Stream<QueryResponse<T>> _cacheResponseStream<T>(
QueryRequest<T> queryRequest) =>
cache
.watchQuery(ReadQueryOptions(
(b) => b
..document = queryRequest.operation.document
..operationName = queryRequest.operation.operationName
..variables = queryRequest.variables,
))
.map(
(data) => QueryResponse(
queryRequest: queryRequest,
data: (data == null || data.isEmpty)
? null
: queryRequest.parseData(data),
),
);
/// Store data in cache
void _writeToCache(QueryResponse response) {
if (response.data != null)
cache.writeQuery(
WriteQueryOptions(
(b) => b
..document = response.queryRequest.operation.document
..operationName = response.queryRequest.operation.operationName
..variables = response.queryRequest.variables
..data = response.data?.data,
),
response.optimistic,
response.queryRequest.queryId,
);
}
/// Run user-defined [UpdateCacheHandler]s with a [CacheProxy]
void _runUpdateCacheHandlers<T>(QueryResponse<T> response) {
final key = response.queryRequest.updateCacheHandlerKey;
if (key == null) return;
final handler = options.updateCacheHandlers[key] as UpdateCacheHandler<T>;
if (handler == null) throw Exception("No handler defined for key $key");
handler(
CacheProxy(
cache,
response.optimistic,
response.queryRequest.queryId,
),
response,
);
}
/// Updates previous result with new result.
///
/// Useful for pagination.
Stream<QueryResponse<T>> _updateResultStream<T>(
Stream<QueryResponse<T>> stream) {
return stream.startWith(null).pairwise().map((results) {
final previousResult = results.first;
final result = results.last;
return result.queryRequest.updateResult == null
? result
: QueryResponse<T>(
data: result.queryRequest.updateResult(
previousResult.data,
result.data,
),
errors: result.errors,
queryRequest: result.queryRequest,
);
});
}
}