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How do I add a custom directive to a query resolved through a singleton

I have managed to add custom directives to the GraphQL schema but I am struggling to work out how to add a custom directive to a field definition. Any hints on the correct implementation would be very helpful.
I am using GraphQL SPQR 0.9.6 to generate my schema

ORIGINAL ANSWER: (now outdated, see the 2 updates below)
It's currently not possible to do this. GraphQL SPQR v0.9.9 will be the first to support custom directives.
Still, in 0.9.8 there's a possible work-around, depending on what you're trying to achieve. SPQR's own meta-data about a field or a type is kept inside custom directives. Knowing that, you can get a hold of the Java method/field underlying the GraphQL field definition. If what you want is e.g. an instrumentation that does something based on a directive, you could instead obtain any annotations on the underlying element, having the full power of Java at your disposal.
The way to get the method would something like:
Operation operation = Directives.getMappedOperation(env.getField()).get();
Resolver resolver = operation.getApplicableResolver(env.getArguments().keySet());
Member underlyingElement = resolver.getExecutable().getDelegate();
UPDATE:
I posted a huge answer on this GitHub issue. Pasting it here as well.
You can register an additional directive as such:
generator.withSchemaProcessors(
(schemaBuilder, buildContext) -> schemaBuilder.additionalDirective(...));
But (according to my current understanding), this only makes sense for query directives (something the client sends as a part of the query, like #skip or #deffered).
Directives like #dateFormat simply make no sense in SPQR: they're there to help you when parsing SDL and mapping it to your code. In SPQR, there's no SDL and you start from your code.
E.g. #dateFormat is used to tell you that you need to provide date formatting to a specific field when mapping it to Java. In SPQR you start from the Java part and the GraphQL field is generated from a Java method, so the method must already know what format it should return. Or it has an appropriate annotation already. In SPQR, Java is the source of truth. You use annotations to provide extra mapping info. Directives are basically annotation in SDL.
Still, field or type level directives (or annotations) are very useful in instrumentations. E.g. if you want to intercept field resolution and inspect the authentication directives.
In that case, I'd suggest you simply use annotations for the same purpose.
public class BookService {
#Auth(roles= {"Admin"}) //example custom annotation
public Book addBook(Book book) { /*insert a Book into the DB */ }
}
As each GraphQLFieldDefinition is backed by a Java methods (or a field), you can get the underlying objects in your interceptor or wherever:
GraphQLFieldDefinition field = ...;
Operation operation = Directives.getMappedOperation(field).get();
//Multiple methods can be hooked up to a single GraphQL operation. This gets the #Auth annotations from all of them
Set<Auth> allAuthAnnotations = operation.getResolvers().stream()
.map(res -> res.getExecutable().getDelegate()) //get the underlying method
.filter(method -> method.isAnnotationPresent(Auth.class))
.map(method -> method.getAnnotation(Auth.class))
.collect(Collectors.toSet());
Or, to inspect only the method that can handle the current request:
DataFetchingEnvironment env = ...; //get it from the instrumentation params
Auth auth = operation.getApplicableResolver(env.getArguments().keySet()).getExecutable().getDelegate().getAnnotation(Auth.class);
Then you can inspect your annotations as you wish, e.g.
Set<String> allNeededRoles = allAuthAnnotations.stream()
.flatMap(auth -> Arrays.stream(auth.roles))
.collect(Collectors.toSet());
if (!currentUser.getRoles().containsAll(allNeededRoles)) {
throw new AccessDeniedException(); //or whatever is appropriate
}
Of course, there's no real need to actually implement authentication this way, as you're probably using a framework like Spring or Guice (maybe even Jersey has the needed security features), that already has a way to intercept all methods and implement security. So you can just use that instead. Much simpler and safer. E.g. for Spring Security, just keep using it as normal:
public class BookService {
#PreAuth(...) //standard Spring Security
public Book addBook(Book book) { /*insert a Book into the DB */ }
}
Make sure you also read my answer on implementing security in GraphQL if that's what you're after.
You can use instrumentations to dynamically filter the results in the same way: add an annotation on a method, access it from the instrumentation, and process the result dynamically:
public class BookService {
#Filter("title ~ 'Monkey'") //example custom annotation
public List<Book> findBooks(...) { /*get books from the DB */ }
}
new SimpleInstrumentation() {
// You can also use beginFieldFetch and then onCompleted instead of instrumentDataFetcher
#Override
public DataFetcher<?> instrumentDataFetcher(DataFetcher<?> dataFetcher, InstrumentationFieldFetchParameters parameters) {
GraphQLFieldDefinition field = parameters.getEnvironment().getFieldDefinition();
Optional<String> filterExpression = Directives.getMappedOperation(field)
.map(operation ->
operation.getApplicableResolver(parameters.getEnvironment().getArguments().keySet())
.getExecutable().getDelegate()
.getAnnotation(Filter.class).value()); //get the filtering expression from the annotation
return filterExpression.isPresent() ? env -> filterResultBasedOn Expression(dataFetcher.get(parameters.getEnvironment()), filterExpression) : dataFetcher;
}
}
For directives on types, again, just use Java annotations. You have access to the underlying types via:
Directives.getMappedType(graphQLType).getAnnotation(...);
This, again, probably only makes sense only in instrumentations. Saying that because normally the directives provide extra info to map SDL to a GraphQL type. In SPQR you map a Java type to a GraphQL type, so a directive makes no sense in that context in most cases.
Of course, if you still need actual GraphQL directives on a type, you can always provide a custom TypeMapper that puts them there.
For directives on a field, it is currently not possible in 0.9.8.
0.9.9 will have full custom directive support on any element, in case you still need them.
UPDATE 2: GraphQL SPQR 0.9.9 is out.
Custom directives are now supported. See issue #200 for details.
Any custom annotation meta-annotated with #GraphQLDirective will be mapped as a directive on the annotated element.
E.g. imagine a custom annotation #Auth(requiredRole = "Admin") used to denote access restrictions:
#GraphQLDirective //Should be mapped as a GraphQLDirective
#Retention(RetentionPolicy.RUNTIME)
#Target({ElementType.METHOD}) //Applicable to methods
public #interface Auth {
String requiredRole();
}
If a resolver method is then annotated with #Auth:
#GraphQLMutation
#Auth(requiredRole = {"Admin"})
public Book addBook(Book newBook) { ... }
The resulting GraphQL field fill look like:
type Mutation {
addBook(newBook: BookInput): Book #auth(requiredRole : "Admin")
}
That is to say the #Auth annotation got mapped to a directive, due to the presence of #GraphQLDirective meta-annotation.
Client directives can be added via: GraphQLSchemaGenerator#withAdditionalDirectives(java.lang.reflect.Type...).
SPQR 0.9.9 also comes with ResolverInterceptors which can intercept the resolver method invocation and inspect the annotations/directives. They are much more convenient to use than Instrumentations, but are not as general (have a much more limited scope). See issue #180 for details, and the related tests for usage examples.
E.g. to make use of the #Auth annotation from above (not that #Auth does not need to be a directive for this to work):
public class AuthInterceptor implements ResolverInterceptor {
#Override
public Object aroundInvoke(InvocationContext context, Continuation continuation) throws Exception {
Auth auth = context.getResolver().getExecutable().getDelegate().getAnnotation(Auth.class);
User currentUser = context.getResolutionEnvironment().dataFetchingEnvironment.getContext();
if (auth != null && !currentUser.getRoles().containsAll(Arrays.asList(auth.rolesRequired()))) {
throw new IllegalAccessException("Access denied"); // or return null
}
return continuation.proceed(context);
}
}
If #Auth is a directive, you can also get it via the regular API, e.g.
List<GraphQLDirective> directives = dataFetchingEnvironment.getFieldDefinition().get.getDirectives();
DirectivesUtil.directivesByName(directives);

Modifying annotation value in superclass and dynamically instantiating child classes with new value

We are using Spring Cloud Stream as the underlying implementation for event messaging in our microservice-based architecture. We wanted to go a step further and provide an abstraction layer between our services and the Spring Cloud Stream library to allow for dynamic channel subscriptions without too much boilerplate configuration code in the services themselves.
The original idea was as follows:
The messaging-library provides a BaseHandler abstract class which all individual services must implement. All handlers of a specific service would like to the same input channel, though only the one corresponding to the type of the event to handle would be called. This looks as follows:
public abstract class BaseEventHandler<T extends Event> {
#StreamListener
public abstract void handle(T event);
}
Each service offers its own events package, which contains N EventHandlers. There are plain POJOs which must be instantiated programmatically. This would look as follows:
public class ServiceEventHandler extends BaseEventHandler<ImportantServiceEvent> {
#Override
public void handle(ImportantServiceEvent event) {
// todo stuff
}
}
Note that these are simple classes and not Spring beans at this point, with ImportantServiceEvent implementing Event.
Our messaging-library is scanned on start-up as early as possible, and performs handler initialization. To do this, the following steps are done:
We scan all available packages in the classpath which provide some sort of event handling and retrieve all subclasses of BaseEventHandler.
We retrieve the #StreamListener annotation in the hierarchy of the subclass, and change its value to the corresponding input channel for this service.
Since our handlers might need to speak to some other application components (repositories etc.), we use DefaultListableBeanFactory to instantiate our handlers as singleton, as follows:
val bean = beanFactory.createBean(eventHandlerClass, AutowireCapableBeanFactory.AUTOWIRE_BY_TYPE, true);
beanFactory.registerSingleton(eventHandlerClass.getSimpleName(), bean);
After this, we ran into several issues.
The Spring Cloud Stream #StreamListener annotation cannot be inherited as it is a method annotation. Despite this, some mechanism seems to be able to find it on the parent (as the StreamListenerAnnotationBeanPostProcessor is registered) and attempts to perform post-processing upon the ServiceEventHandler being initialized. Our assumption is that the Spring Cloud Stream uses something like AnnotationElementUtils.findAllMergedAnnotations().
As a result of this, we thought that we might be able to alter the annotation value of the base class prior to each instantiation of a child class. Due to this, we thought that although our BaseEventHandler would simply get a new value which would then stay constant at the end of this initialization phase, the child classes would be instantiated with the correct channel name at the time of instantiation, since we do not expect to rebind. However, this is not the case and the value of the #StreamListener annotation that is used is always the one on the base.
The question is then: is what we want possible with Spring Cloud Stream? Or is it rather a plain Java problem that we have here (does not seem to be the case)? Did the Spring Cloud Stream team foresee a use case like this, and are we simply doing it completely wrong?
This question was also posted on on the Spring Cloud Stream tracker in case it might help garner a bit more attention.

Since the same people monitor SO and GitHub issues, it's rather pointless to post in both places. Stack Overflow is preferred for questions.
You should be able to subclass the BPP; it specifically has this extension point:
/**
* Extension point, allowing subclasses to customize the {#link StreamListener}
* annotation detected by the postprocessor.
*
* #param originalAnnotation the original annotation
* #param annotatedMethod the method on which the annotation has been found
* #return the postprocessed {#link StreamListener} annotation
*/
protected StreamListener postProcessAnnotation(StreamListener originalAnnotation, Method annotatedMethod) {
return originalAnnotation;
}
Then override the bean definition with yours
#Bean(name = STREAM_LISTENER_ANNOTATION_BEAN_POST_PROCESSOR_NAME)
public static StreamListenerAnnotationBeanPostProcessor streamListenerAnnotationBeanPostProcessor() {
return new StreamListenerAnnotationBeanPostProcessor();
}

Guice injection for dynamically creating objects

I have a "Handler" interface for a message queue, something that has methods:
boolean canHandle(message);
void handle(message);
I then have multiple implementations for this interface, each of them canHandle() certain types of messages
When a message arrive, I do something like:
for (Handler handler : handlers) {
if handler.canHandle(message)
handle(message)
So, I need to build a list of "enabled handlers" that must be specified in a config file.
I could either specify the enabled handlers by class name (FQCN) or annotating the class by some name and referencing this name on the config.
For instance:
enabledHandlers = ("com.domain.handlers.HandlerA", "com.domain.handlers.HandlerB", )
#or
enabledHandlers = ("HandlerAAnnotation", "HandlerBAnnotation", )
in any case, somehow I will need to build those handlers inside my service, and they require injected parameters.
I believe something injector.getInstance(clazz) would work to build those objects, but it doesn't make much sense to have the "injector" going around my service when I need to create those classes.
I could also create them by reflection "manually" by clazz.getConstructor(...).newInstance(...), but it seems pretty dirty.
Any other ideas?
Thanks!

Hibernate 5 entity listeners with Guice

I'm playing with the new Hibernate 5 Bootstrap API and was excited to see how easily (compared to previous/legacy API) can assemble SessionFactory and family.
Now, I would like to provide my own ListenerFactory which basically delegates creation and dependency injection of entity listeners to Guice.
I couldn't find how to do it except for applyBeanManager from SessionFactoryBuilder:
sessionFactoryBuilder.applyBeanManager(new ListenerFactory() {
#Override
public void release() {
}
#Override
public <T> Listener<T> buildListener(final Class<T> listenerClass) {
return () -> injector.getInstance(listenerClass);
}
});
Unfortunately, this didn't work bc Hibernate expect ListenerFactory to be null (and uses a default ListenerFactory) or be an instance of BeanManager.
Wonder if there is another way of provide my own ListenerFactory?
Thanks.

That's because the BeanManager is designed for CDI. If you want to customize it beyond CDI, you need to open JIRA issue describing your use case and what you want to do.
Alternatively, if you want to inject dependencies into your entities (which I find really odd since it breaks layer encapsulation), you could just use the LoadEventListener to customize the way an entity is created:
sessionFactory
.getServiceRegistry()
.getService( EventListenerRegistry.class )
.prependListeners( EventType.LOAD, new MyGuiceEntityListener() );

Best factory pattern for delivering app data object based on application type in http header

I have a business with multiple applications using my webservice resource. I have a web service resource that looks in a http header for the application ID. This tell the server which application is requesting data. My goal is to deliver to my web application developers a method they can call to retrieve all the application specific settings via the application ID.
Given an applicationID i can specify device type, properties file for that app, and whether GCM,APNS or Microsoft Push Notification, etc. So each applicationID has distinct properties basically.
I want the developer to be able to call for this object like this (or similar):
ApplicationData appData = ApplicationDataFactory.getCurrentApplicationData();
and the factory would look something like this:
class ApplicationDataFactory
{
public static ApplicationData getCurrentApplicationData()
{
//notice how im not passing in criteria here, im getting it from the request so call doens't have to know
String criteria = Request.getHTTPHeaderInfo("applicationID");
if ( criteria.equals("Android") )
return new Android();
else if ( criteria.equals("Android-germany") )
return new Android_germany();
else if ( criteria.equals("ios_germany") )
return new ios_germany();
else if ( criteria.equals("ios"))
return new ios();
else if ( criteria.equals("windows") )
return new windows();
return null;//or throw exception
}
}
so Android, ios, and windows objects all extend off ApplicationData class clearly.
So for example the Android.java object would look like this:
class Android extends ApplicationData{
#override
public String getType(){
return "Android"
}
#override
public Properties getProperties{
return system.getProperties("android.properties");
}
}
and the Android-germany and ios-germany will have common data since there both from germany.
First, i dont like that im specifying the criteria inside the factory and also can anyone help me
with a good design pattern i can use to achieve this ? Remember, in the end i want to be able to have the developer call only ApplicationDataFactory.getCurrentApplicationData(); (or something similar) and the correct application info will be sent referenced. I dont have to use a factory here either its just the first thing i thought of.

So your problem is with the fact that the logic for the criteria is within the factory method. Meanwhile, you don't want the user to provide the criteria as an parameter to the factor method.
First of all, I don't like the idea of having a static Request class. A request should be an object that contains information about the current request. I have a suspicion that your code may be prone to race conditions, once you have many concurrent requests (how do you know which request is which?). So as a starting point, I would refactor the Request class so that you work with instances of Request.
I think, the clearest approach would be that you pass in applicationID as a parameter. This makes testability trivial and the code becomes very obvious, too. You take an input and produce the output based on the input. You could pass the Request instead of the applicationID and let the factory handle the retrieval of the applicationID from the request (as you are doing now).
If you think the Request -> applicationID logic should not be part of the factory, you can create another class, such as ApplicationIDResolver which translates a Request to an applicationID. From then on ApplicationDataFactory would be used through an instance and the ApplicationIDResolver would be a constructor parameter. (I think, this is an overkill.). Another option is to add a getApplicationID() method to the Request class.
If you use a dependency injection framework, it may take care of object life cycles/scopes automatically for you, so the ApplicationData could be a request-scoped object and you could tell your dependency injection framework to instantiate ApplicationData objects based on requests and inject them into the classes where they get used.

Better to use for this purposes enum which implements ApplicationData interface and define each entry. You can resolve proper by valueOf() from enum.