Support querying`@DocumentReference` with QueryDsl

[ArayChou]

Hello, here is the demo project: https://github.com/ArayChou/spring-data-mongodb-test. Run the class test.ExampleApplication to start it. (it needs a local default installed MongoDB server)

spring-data-mongodb: 3.3.4
querydsl-mongodb: 5.0.0
mongodb-driver-sync: 4.4.2

@Document
public class Kid {
    @Id
    private String id;
    private String name;
    @DocumentReference
    private Mother mother;
    @DBRef
    private Father father;

// ommiting setters and getters 
}

    @Autowired
    private KidRepository repository;

    public void test() {

        // @DBRef annotated field works
        repository.findAll(QKid.kid.father.id.eq(this.fatherId)).forEach(System.out::println);

        //TODO To query @DocumentReference annotated field Kid.mother won't work
        repository.findAll(QKid.kid.mother.id.eq(this.motherId)).forEach(System.out::println);
    }

Field Kid.mother is annotated with @DocumentReference. repository.findAll(QKid.kid.mother.id.eq(this.motherId)) will throw exception, it should work just as @DBREF.

Exception in thread "main" java.lang.IllegalArgumentException: The referenced property has to be mapped with @DBRef!
	at org.springframework.util.Assert.isTrue(Assert.java:121)
	at org.springframework.data.mongodb.core.convert.MappingMongoConverter.toDBRef(MappingMongoConverter.java:590)
	at org.springframework.data.mongodb.repository.support.SpringDataMongodbSerializer.asReference(SpringDataMongodbSerializer.java:149)
	at org.springframework.data.mongodb.repository.support.SpringDataMongodbSerializer.convert(SpringDataMongodbSerializer.java:189)
	at com.querydsl.mongodb.document.MongodbDocumentSerializer.visit(MongodbDocumentSerializer.java:108)
	at com.querydsl.mongodb.document.MongodbDocumentSerializer.visit(MongodbDocumentSerializer.java:41)
	at com.querydsl.core.types.OperationImpl.accept(OperationImpl.java:88)
	at com.querydsl.mongodb.document.MongodbDocumentSerializer.handle(MongodbDocumentSerializer.java:44)
	at com.querydsl.mongodb.document.AbstractMongodbQuery.createQuery(AbstractMongodbQuery.java:206)
	at org.springframework.data.mongodb.repository.support.SpringDataMongodbQuery.createQuery(SpringDataMongodbQuery.java:248)
	at org.springframework.data.mongodb.repository.support.SpringDataMongodbQuery.createQuery(SpringDataMongodbQuery.java:240)
	at org.springframework.data.mongodb.repository.support.SpringDataMongodbQuery.fetch(SpringDataMongodbQuery.java:161)
	at org.springframework.data.mongodb.repository.support.QuerydslMongoPredicateExecutor.findAll(QuerydslMongoPredicateExecutor.java:113)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at org.springframework.data.repository.core.support.RepositoryMethodInvoker$RepositoryFragmentMethodInvoker.lambda$new$0(RepositoryMethodInvoker.java:289)
	at org.springframework.data.repository.core.support.RepositoryMethodInvoker.doInvoke(RepositoryMethodInvoker.java:137)
	at org.springframework.data.repository.core.support.RepositoryMethodInvoker.invoke(RepositoryMethodInvoker.java:121)
	at org.springframework.data.repository.core.support.RepositoryComposition$RepositoryFragments.invoke(RepositoryComposition.java:529)
	at org.springframework.data.repository.core.support.RepositoryComposition.invoke(RepositoryComposition.java:285)
	at org.springframework.data.repository.core.support.RepositoryFactorySupport$ImplementationMethodExecutionInterceptor.invoke(RepositoryFactorySupport.java:639)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.doInvoke(QueryExecutorMethodInterceptor.java:163)
	at org.springframework.data.repository.core.support.QueryExecutorMethodInterceptor.invoke(QueryExecutorMethodInterceptor.java:138)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
	at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:80)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
	at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:97)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215)
	at jdk.proxy2/jdk.proxy2.$Proxy53.findAll(Unknown Source)
	at test.QueryDslTest.test(QueryDslTest.java:22)
	at test.ExampleApplication.main(ExampleApplication.java:15)

Thanks & Regards.