Reputation: 5987
I am currently in the middle of migrating my REST-Server to GraphQL (at least partly). Most of the work is done, but i stumbled upon this problem which i seem to be unable to solve: OneToMany relationships in a graphql query, with FetchType.LAZY.
I am using: https://github.com/graphql-java/graphql-spring-boot and https://github.com/graphql-java/graphql-java-tools for the integration.
Here is an example:
Entities:
@Entity
class Show {
private Long id;
private String name;
@OneToMany(mappedBy = "show")
private List<Competition> competition;
}
@Entity
class Competition {
private Long id;
private String name;
@ManyToOne(fetch = FetchType.LAZY)
private Show show;
}
Schema:
type Show {
id: ID!
name: String!
competitions: [Competition]
}
type Competition {
id: ID!
name: String
}
extend type Query {
shows : [Show]
}
Resolver:
@Component
public class ShowResolver implements GraphQLQueryResolver {
@Autowired
private ShowRepository showRepository;
public List<Show> getShows() {
return ((List<Show>)showRepository.findAll());
}
}
If i now query the endpoint with this (shorthand) query:
{
shows {
id
name
competitions {
id
}
}
}
i get:
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: Show.competitions, could not initialize proxy - no Session
Now i know why this error happens and what it means, but i don't really know were to apply a fix for this. I don't want to make my entites to eagerly fetch all relations, because that would negate some of the advantages of GraphQL. Any ideas where i might need to look for a solution? Thanks!
Upvotes: 18
Views: 7926
Reputation: 1269
As Oleg pointed out, the error handling using AsyncTransactionalExecutionStrategy
is broken inside nested transactions.
Since the URL in his answer does not work anymore, here is how I have solved it.
First lets have some exception I want to properly handle through GraphQL response
public class UserFriendlyException extends RuntimeException {
public UserFriendlyException(String message) {
super(message);
}
}
Then I defined error response
public class UserFriendlyGraphQLError implements GraphQLError {
/** Message shown to user */
private final String message;
private final List<SourceLocation> locations;
private final ExecutionPath path;
public UserFriendlyGraphQLError(String message, List<SourceLocation> locations, ExecutionPath path) {
this.message = message;
this.locations = locations;
this.path = path;
}
@Override
public String getMessage() {
return message;
}
@Override
public List<SourceLocation> getLocations() {
return locations;
}
@Override
public ErrorClassification getErrorType() {
return CustomErrorClassification.USER_FRIENDLY_ERROR;
}
@Override
public List<Object> getPath() {
return path.toList();
}
}
public enum CustomErrorClassification implements ErrorClassification {
USER_FRIENDLY_ERROR
}
Then I created DataFetcherExceptionHandler
to transform it into proper GraphQL response
/**
* Converts exceptions into error response
*/
public class GraphQLExceptionHandler implements DataFetcherExceptionHandler {
private final DataFetcherExceptionHandler delegate = new SimpleDataFetcherExceptionHandler();
@Override
public DataFetcherExceptionHandlerResult onException(DataFetcherExceptionHandlerParameters handlerParameters) {
// handle user friendly errors
if (handlerParameters.getException() instanceof UserFriendlyException) {
GraphQLError error = new UserFriendlyGraphQLError(
handlerParameters.getException().getMessage(),
List.of(handlerParameters.getSourceLocation()),
handlerParameters.getPath());
return DataFetcherExceptionHandlerResult.newResult().error(error).build();
}
// delegate to default handler otherwise
return delegate.onException(handlerParameters);
}
}
And finally used it in the AsyncTransactionalExecutionStrategy
, using also the @Transactional
annotation to allow lazy resolvers
@Component
public class AsyncTransactionalExecutionStrategy extends AsyncExecutionStrategy {
public AsyncTransactionalExecutionStrategy() {
super(new GraphQLExceptionHandler());
}
@Override
@Transactional
public CompletableFuture<ExecutionResult> execute(ExecutionContext executionContext, ExecutionStrategyParameters parameters) throws NonNullableFieldWasNullException {
return super.execute(executionContext, parameters);
}
}
Now if you throw new UserFriendlyException("Email already exists");
somewhere you would end up with nice response like
{
"errors": [
{
"message": "Email already exists",
"locations": [
{
"line": 2,
"column": 3
}
],
"path": [
"createUser"
],
"extensions": {
"classification": "USER_FRIENDLY_ERROR"
}
}
],
"data": null
}
Given the classification USER_FRIENDLY_ERROR
you can directly show it to the user, if you made UserFriendlyException
messages user-friendly :)
However if you throw new UserFriendlyException("Email already exists");
inside some method annotated with @Transactional
you end up with empty response and HTTP 400 status.
Adding @Transactional(propagation = Propagation.REQUIRES_NEW)
to Mutation
solves this issue
@Transactional(propagation = Propagation.REQUIRES_NEW)
public class Mutation implements GraphQLMutationResolver {
public User createUser(...) {
...
}
}
Note that this is probably not so performant solution. However it could suffice for some smaller projects.
Upvotes: 0
Reputation: 5987
I solved it and should have read the documentation of the graphql-java-tools library more carefully i suppose.
Beside the GraphQLQueryResolver
which resolves the basic queries i also needed a GraphQLResolver<T>
for my Show
class, which looks like this:
@Component
public class ShowResolver implements GraphQLResolver<Show> {
@Autowired
private CompetitionRepository competitionRepository;
public List<Competition> competitions(Show show) {
return ((List<Competition>)competitionRepository.findByShowId(show.getId()));
}
}
This tells the library how to resolve complex objects inside my Show
class and is only used if the initially query requests to include the Competition
objects. Happy new Year!
EDIT 31.07.2019: I since stepped away from the solution below. Long running transactions are seldom a good idea and in this case it can cause problems once you scale your application. We started to implement DataLoaders to batch queries in an async matter. The long running transactions in combination with the async nature of the DataLoaders can lead to deadlocks: https://github.com/graphql-java-kickstart/graphql-java-tools/issues/58#issuecomment-398761715 (above and below for more information). I will not remove the solution below, because it might still be good starting point for smaller applications and/or applications which will not need any batched queries, but please keep this comment in mind when doing so.
EDIT: As requested here is another solution using a custom execution strategy. I am using graphql-spring-boot-starter
and graphql-java-tools
:
Create a Bean of type ExecutionStrategy
that handles the transaction, like this:
@Service(GraphQLWebAutoConfiguration.QUERY_EXECUTION_STRATEGY)
public class AsyncTransactionalExecutionStrategy extends AsyncExecutionStrategy {
@Override
@Transactional
public CompletableFuture<ExecutionResult> execute(ExecutionContext executionContext, ExecutionStrategyParameters parameters) throws NonNullableFieldWasNullException {
return super.execute(executionContext, parameters);
}
}
This puts the whole execution of the query inside the same transaction. I don't know if this is the most optimal solution, and it also already has some drawbacks in regards to error handling, but you don't need to define a type resolver that way.
Notice that if this is the only ExecutionStrategy
Bean present, this will also be used for mutations, contrary to what the Bean name might suggest. See https://github.com/graphql-java-kickstart/graphql-spring-boot/blob/v11.1.0/graphql-spring-boot-autoconfigure/src/main/java/graphql/kickstart/spring/web/boot/GraphQLWebAutoConfiguration.java#L161-L166 for reference. To avoid this define another ExecutionStrategy
to be used for mutations:
@Bean(GraphQLWebAutoConfiguration.MUTATION_EXECUTION_STRATEGY)
public ExecutionStrategy queryExecutionStrategy() {
return new AsyncSerialExecutionStrategy();
}
Upvotes: 14
Reputation: 672
For me using AsyncTransactionalExecutionStrategy
worked incorrectly with exceptions. E.g. lazy init or app-level exception triggered transaction to rollback-only status. Spring transaction mechanism then threw on rollback-only transaction at the boundary of strategy execute
, causing HttpRequestHandlerImpl
to return 400 empty response. See https://github.com/graphql-java-kickstart/graphql-java-servlet/issues/250 and https://github.com/graphql-java/graphql-java/issues/1652 for more details.
What worked for me was using Instrumentation
to wrap the whole operation in a transaction: https://spectrum.chat/graphql/general/transactional-queries-with-spring~47749680-3bb7-4508-8935-1d20d04d0c6a
Upvotes: 0
Reputation: 818
My prefered solution is to have the transaction open until the Servlet sends its response. With this small code change your LazyLoad will work right:
import javax.servlet.Filter;
import org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter;
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
/**
* Register the {@link OpenEntityManagerInViewFilter} so that the
* GraphQL-Servlet can handle lazy loads during execution.
*
* @return
*/
@Bean
public Filter OpenFilter() {
return new OpenEntityManagerInViewFilter();
}
}
Upvotes: 18
Reputation: 1316
For anyone confused about the accepted answer then you need to change the java entities to include a bidirectional relationship and ensure you use the helper methods to add a Competition
otherwise its easy to forget to set the relationship up correctly.
@Entity
class Show {
private Long id;
private String name;
@OneToMany(cascade = CascadeType.ALL, mappedBy = "show")
private List<Competition> competition;
public void addCompetition(Competition c) {
c.setShow(this);
competition.add(c);
}
}
@Entity
class Competition {
private Long id;
private String name;
@ManyToOne(fetch = FetchType.LAZY)
private Show show;
}
The general intuition behind the accepted answer is:
The graphql resolver ShowResolver
will open a transaction to get the list of shows but then it will close the transaction once its done doing that.
Then the nested graphql query for competitions
will attempt to call getCompetition()
on each Show
instance retrieved from the previous query which will throw a LazyInitializationException
because the transaction has been closed.
{
shows {
id
name
competitions {
id
}
}
}
The accepted answer is essentially
bypassing retrieving the list of competitions through the OneToMany
relationship and instead creates a new query in a new transaction which eliminates the problem.
Not sure if this is a hack but @Transactional
on resolvers doesn't work for me although the logic of doing that does make some sense but I am clearly not understanding the root cause.
Upvotes: 2
Reputation: 9445
You just need to annotate your resolver classes with @Transactional
. Then, entities returned from repositories will be able to lazily fetch data.
Upvotes: -4
Reputation: 53
I am assuming that whenever you fetch an object of Show, you want all the associated Competition of the Show object.
By default the fetch type for all collections type in an entity is LAZY. You can specify the EAGER type to make sure hibernate fetches the collection.
In your Show class you can change the fetchType to EAGER.
@OneToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
private List<Competition> competition;
Upvotes: -4