Inject bean into DataFetcher of GraphQL

问题

I'm using Spring & graphql-java (graphql-java-annotation) in my project. For retrieving data part, i'm using a DataFetcher to get data from a service (from database).

The weird thing is that: myService is always null. Anyone know the reason?

DataFetcher

@Component
public class MyDataFetcher implements DataFetcher {

    // get data from database
    @Autowired
    private MyService myService;

    @Override
    public Object get(DataFetchingEnvironment environment) {
        return myService.getData();
    }
}

Schema

@Component
@GraphQLName("Query")
public class MyGraphSchema {

    @GraphQLField
    @GraphQLDataFetcher(MyDataFetcher.class)
    public Data getData() {
        return null;
    }
}

MyService

@Service
public class MyService {

    @Autowired
    private MyRepository myRepo;

    @Transactional(readOnly = true)
    public Data getData() {
        return myRepo.getData();
    }
}

Main test

@Bean
public String testGraphql(){
    GraphQLObjectType object = GraphQLAnnotations.object(MyGraphSchema.class);
    GraphQLSchema schema = newSchema().query(object).build();
    GraphQL graphql = new GraphQL(schema);

    ExecutionResult result = graphql.execute("{getData {id name desc}}");;
    Map<String, Object> v = (Map<String, Object>) result.getData();
    System.out.println(v);
    return v.toString();
}

回答1:

Since in graphql-java-annotation the data fetcher is defined by annotation, it is constructed by the framework (using reflection to get the constructor), thus it can't be a bean.

The workaround I've found for this is setting it as ApplicationContextAware, and then I can initialize some static field instead of a bean. Not the nicest thing, but it works:

@Component
public class MyDataFetcher implements DataFetcher, ApplicationContextAware {

    private static MyService myService;
    private static ApplicationContext context;

    @Override
    public Object get(DataFetchingEnvironment environment) {
        return myService.getData();
    }

    @override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansExcepion {
        context = applicationContext;
        myService = context.getBean(MyService.class);
    }
}

Basically you'll still get a new instance of the data fetcher initialized by graphQL, but also spring will initialize it, and since the myService is static, you'll get the initialized one.

回答2:

The solution provided by @Nir Levy works perfectly. Just to make it a bit more reusable here. We can extract an abstract class which encapsulate the bean lookup logic and make autowiring work for its subclasses.

public abstract class SpringContextAwareDataFetcher implements DataFetcher, ApplicationContextAware {

    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    @Override
    public final Object get(DataFetchingEnvironment environment) {
        return applicationContext.getBean(this.getClass()).fetch(environment);
    }

    protected abstract Object fetch(DataFetchingEnvironment environment);
}

And the subclass can be like this:

@Component
public class UserDataFetcher extends SpringContextAwareDataFetcher {

    @Autowired
    private UserService userService;

    @Override
    public String fetch(DataFetchingEnvironment environment) {
        User user = (User) environment.getSource();
        return userService.getUser(user.getId()).getName();
    }
}

回答3:

Though @Nir's approach works (and I often use it inside JPA Event Listeners), the DataFetcher objects are Singletons, so injecting via static properties is a little hacky.

However, GraphQL's execute method allows you to pass in an object as a context, which will then be available in your DataFetchingEnvironment object inside of your DataFetcher (see the graphql.execute() line below):

@Component
public class GraphQLService {

    @Autowired
    MyService myService;

    public Object getGraphQLResult() {
        GraphQLObjectType object = GraphQLAnnotations.object(MyGraphSchema.class);
        GraphQLSchema schema = newSchema().query(object).build();
        GraphQL graphql = new GraphQL(schema);

        ExecutionResult result = graphql.execute("{getData {id name desc}}", myService);

        return result.getData();
    }
}

public class MyDataFetcher implements DataFetcher {

    @Override
    public Object get(DataFetchingEnvironment environment) {
        MyService myService = (MyService) environment.getContext();

        return myService.getData();
    }
}

来源：https://stackoverflow.com/questions/41440026/inject-bean-into-datafetcher-of-graphql

标签

java

Spring

graphql

graphql-java