Unable to determine data class for resolver '...' from generic interface! This is most likely a bug with graphql-java-tools.

[mxmlnglt]

using this version of the kickstart:

        <dependency>
            <groupId>com.graphql-java-kickstart</groupId>
            <artifactId>graphql-spring-boot-starter</artifactId>
            <version>5.10.0</version>
        </dependency>

my GraphQL schema:

interface Mother {
  # Mother fields
}

type Child implements Mother {
  # Child & Mother's fields
}

my Java classes:

public class Mother {
    // Mother's fields
}

public class Child extends Mother {
    // Child's fields
}

@Component
public abstract class MotherResolver<T extends Mother> implements GraphQLResolver<T> {
    // Resolving methods for Mother's fields
}

@Component
public class ChildResolver extends MotherResolver<Child> {
    // Resolving methods for Child's fields
}

Starting my Spring Boot app, I get the following stack trace:

Caused by: com.coxautodev.graphql.tools.ResolverError: Unable to determine data class for resolver 'com.company.app.graphql.resolver.ChildResolver' from generic interface! This is most likely a bug with graphql-java-tools.
    at com.coxautodev.graphql.tools.NormalResolverInfo.findDataClass(ResolverInfo.kt:31) ~[graphql-java-tools-5.6.1.jar:na]
    at com.coxautodev.graphql.tools.NormalResolverInfo.<init>(ResolverInfo.kt:19) ~[graphql-java-tools-5.6.1.jar:na]
    at com.coxautodev.graphql.tools.SchemaClassScanner$resolverInfos$1.invoke(SchemaClassScanner.kt:38) ~[graphql-java-tools-5.6.1.jar:na]
    at com.coxautodev.graphql.tools.SchemaClassScanner$resolverInfos$1.invoke(SchemaClassScanner.kt:26) ~[graphql-java-tools-5.6.1.jar:na]
    at kotlin.sequences.TransformingSequence$iterator$1.next(Sequences.kt:174) ~[kotlin-stdlib-1.3.10.jar:1.3.10-release-253 (1.3.10)]
    at kotlin.sequences.SequencesKt___SequencesKt.toCollection(_Sequences.kt:691) ~[kotlin-stdlib-1.3.10.jar:1.3.10-release-253 (1.3.10)]
    at kotlin.sequences.SequencesKt___SequencesKt.toMutableList(_Sequences.kt:721) ~[kotlin-stdlib-1.3.10.jar:1.3.10-release-253 (1.3.10)]
    at kotlin.sequences.SequencesKt___SequencesKt.toList(_Sequences.kt:712) ~[kotlin-stdlib-1.3.10.jar:1.3.10-release-253 (1.3.10)]
    at com.coxautodev.graphql.tools.SchemaClassScanner.<init>(SchemaClassScanner.kt:38) ~[graphql-java-tools-5.6.1.jar:na]
    at com.coxautodev.graphql.tools.SchemaParserBuilder.scan(SchemaParserBuilder.kt:164) ~[graphql-java-tools-5.6.1.jar:na]
    at com.coxautodev.graphql.tools.SchemaParserBuilder.build(SchemaParserBuilder.kt:206) ~[graphql-java-tools-5.6.1.jar:na]
    at com.oembedler.moon.graphql.boot.GraphQLJavaToolsAutoConfiguration.schemaParser(GraphQLJavaToolsAutoConfiguration.java:98) ~[graphql-spring-boot-autoconfigure-5.10.0.jar:na]
    at com.oembedler.moon.graphql.boot.GraphQLJavaToolsAutoConfiguration$$EnhancerBySpringCGLIB$$3914e3f2.CGLIB$schemaParser$3(<generated>) ~[graphql-spring-boot-autoconfigure-5.10.0.jar:na]
    at com.oembedler.moon.graphql.boot.GraphQLJavaToolsAutoConfiguration$$EnhancerBySpringCGLIB$$3914e3f2$$FastClassBySpringCGLIB$$27868fdb.invoke(<generated>) ~[graphql-spring-boot-autoconfigure-5.10.0.jar:na]
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) ~[spring-core-5.1.9.RELEASE.jar:5.1.9.RELEASE]
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:363) ~[spring-context-5.1.9.RELEASE.jar:5.1.9.RELEASE]
    at com.oembedler.moon.graphql.boot.GraphQLJavaToolsAutoConfiguration$$EnhancerBySpringCGLIB$$3914e3f2.schemaParser(<generated>) ~[graphql-spring-boot-autoconfigure-5.10.0.jar:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_212]
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_212]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_212]
    at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_212]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.1.9.RELEASE.jar:5.1.9.RELEASE]
    ... 138 common frames omitted

I've seen these (somehow) related issues: https://github.com/graphql-java-kickstart/graphql-java-tools/issues/145 https://github.com/graphql-java-kickstart/graphql-java-tools/issues/163 but with the solution you give in the last comment, I don't understand how I would be able to do something like:

class BazResolver extends FooResolver<Baz> {

}

... because that means this resolver is actually a GraphQLResolver<Bar> which makes no sense at all (from a Java inheritance scheme point of view)!!

Or maybe it's just an erroneous copy/paste from https://github.com/graphql-java-kickstart/graphql-java-tools/issues/331...? (but that's doesn't solve my problem still...)

[mxmlnglt]

My only workaround for now is to move the implements GraphQLResolver<T> to the actual resolver:

@Component
public abstract class MotherResolver<T extends Mother> implements GraphQLResolver<T> { // can be removed from here, it's totally useless...
    // Resolving methods for Mother's fields
}

@Component
public class ChildResolver extends MotherResolver<Child> implements GraphQLResolver<Child> { // totally needed here
    // Resolving methods for Child's fields
}

Edit: fixed from GraphQLResolver<T> to GraphQLResolver<Child> in the ChildResolver, thanks @geeseen

[geesen]

@Component
public class ChildResolver extends MotherResolver<Child> implements GraphQLResolver<T> { // totally needed here
    // Resolving methods for Child's fields
}

Did you mean:

@Component public class ChildResolver extends MotherResolver<Child> implements GraphQLResolver<Child> { ...}

?

[mxmlnglt]

@Component
public class ChildResolver extends MotherResolver<Child> implements GraphQLResolver<T> { // totally needed here
    // Resolving methods for Child's fields
}

Did you mean:

@Component public class ChildResolver extends MotherResolver<Child> implements GraphQLResolver<Child> { ...}

?

Oh yeah, right, I missed this before posting (probably just a copy-paste problem).

[geesen]

Ok, as suspected ;-) Unfortunately, it doesn't work for me if I move the GraphQLResolver from the superclass down to the actual class, when there is also a generic typed method in the super class.

For example, if I have the following:

@Component
public abstract class MotherResolver<T extends Mother> { 

     public T getNext(){
        return ...
     }        
}

This is not working (No type variable found for T)

@Component
public class ChildResolver extends MotherResolver<Child> implements GraphQLResolver<Child> { 

}

But, if I explicitly overwrite the method and call its super method, it is working:

@Component
public class ChildResolver extends MotherResolver<Child> implements GraphQLResolver<Child> { 

    public Child  getNext(){
        return super.getNext();
     }        
}

Of course, this is only an interim solution, because the child resolvers are then inflated unnecessarily and the advantage of Java inheritance does not pay off here - quite apart from the non-existing DRY principle.

Normally, you should be able to define methods centrally in the MotherResolver, which then also apply to all ChildResolvers, without having to touch the ChildResolver individually.

[mxmlnglt]

Normally, you should be able to define methods centrally in the MotherResolver, which then also apply to all ChildResolvers, without having to touch the ChildResolver individually.

Yes, exactly. That's what I do.

[geesen]

Normally, you should be able to define methods centrally in the MotherResolver, which then also apply to all ChildResolvers, without having to touch the ChildResolver individually.

Yes, exactly. That's what I do.

And it is working for you?

[guodage]

graphql-java-tools could not parse the <T> in MotherResolver<T extends SomeObj> implements GraphQLResolver<T>, we need do this.

[matsmad]

Any updates on this?

I'm building a sample project and trying to build a common Resolver to resolve properties of classes at one place For example

public interface MyInterface {
    String getSome();
}

public class ClassA implementes  MyInterface {
    String getSome();
// further props
}

public classB implements MyInterface {
    String getSome();
// further props
}

public class MyAweseomeResolver<T extends MyInterface> implements GraphQLResolver<T> {
    public String getSomeString(final T concrete) {
         return concrete.getSome().toUpperCase()
    }
}

Background: I don't want to implement a resolver for each class which are at least doing the same. I just want to have one resolver which applies to all classes implementing one interface.

[mxmlnglt]

@matsmad AFAIK there has been no intervention from someone of the team here; so you'll probably have to apply my workaround: https://github.com/graphql-java-kickstart/graphql-java-tools/issues/349#issuecomment-570226121