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Generate list-of-interface getters on Java interfaces #953

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54 changes: 19 additions & 35 deletions ...ore/src/main/kotlin/com/netflix/graphql/dgs/codegen/generators/java/InterfaceGenerator.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -78,28 +78,7 @@ class InterfaceGenerator(
val mergedFieldDefinitions = definition.fieldDefinitions + extensions.flatMap { it.fieldDefinitions }

mergedFieldDefinitions.filterSkipped().forEach {
// Generate getters/setters for fields that are not interfaces, and only getters for fields that are interfaces
// unless generateInterfaceMethodsForInterfaceFields && generateInterfaceSetters.
// Skip generating interface methods with list types where the inner type is an interface as Java does not
// support overriding them with more specific types (i.e. List<Dog> does not override List<Pet>).
//
// interface Pet {
// parent: Pet
// }
// type Dog implements Pet {
// parent: Dog
// }
// type Bird implements Pet {
// parent: Bird
// }
// For the schema above, we currently generate Dog::setParent(Dog dog), but the interface
// would have Pet::setParent(Pet pet) leading to missing overrides in the generated
// implementation classes. This is not an issue if the overridden field has the same base type,
// however.
// Ref: https://github.com/graphql/graphql-js/issues/776
if (!isListOfInterface(it.type) || config.generateInterfaceMethodsForInterfaceFields) {
addInterfaceMethod(it, javaType)
}
addInterfaceMethod(it, javaType)
}

val implementations =
Expand Down Expand Up @@ -128,19 +107,24 @@ class InterfaceGenerator(
.getDefinitionsOfType(InterfaceTypeDefinition::class.java)
.any { node -> node.name == typeUtils.findInnerType(fieldDefinition.type).name }

// Returns true if the field is a list type (possibly nested or non-null) with an innermost type that is an interface
private fun isListOfInterface(fieldType: Type<*>): Boolean =
when (fieldType) {
is ListType -> {
val innerType = typeUtils.findInnerType(fieldType)
document
.getDefinitionsOfType(InterfaceTypeDefinition::class.java)
.any { node -> node.name == innerType.name }
}
is NonNullType -> isListOfInterface(fieldType.type)
else -> false
}

// Generate getters/setters for fields. Do not generate setters for fields that are also interfaces, unless forced
// with generateInterfaceMethodsForInterfaceFields.
//
// interface Pet {
// parent: Pet
// }
// type Dog implements Pet {
// parent: Dog
// }
// type Bird implements Pet {
// parent: Bird
// }
//
// For the schema above, we currently generate Dog::setParent(Dog dog), but the interface
// would have Pet::setParent(Pet pet) leading to missing overrides in the generated
// implementation classes. This is not an issue if the overridden field has the same base type,
// however.
// Ref: https://github.com/graphql/graphql-js/issues/776
private fun addInterfaceMethod(
fieldDefinition: FieldDefinition,
javaType: TypeSpec.Builder,
Expand Down
8 changes: 6 additions & 2 deletions ...codegen-core/src/main/kotlin/com/netflix/graphql/dgs/codegen/generators/java/TypeUtils.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,9 @@ class TypeUtils(
var canUseWildcardType = false
if (useWildcardType) {
if (typeName is ClassName) {
if (document.definitions
if (isFieldTypeAnInterface(node.type)) {

@ryanflegel ryanflegel Aug 27, 2026

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Use wildcards for List of interface.

canUseWildcardType = true
} else if (document.definitions
.filterIsInstance<ObjectTypeDefinition>()
.any { e -> "I${e.name}" == typeName.simpleName() } ||
(
Expand All @@ -107,6 +109,8 @@ class TypeUtils(
) {
canUseWildcardType = true
}
} else if (typeName is ParameterizedTypeName && typeName.rawType().canonicalName() == "java.util.List") {

@ryanflegel ryanflegel Aug 27, 2026

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Also use wildcard for List of List (of List...).

This ensure List<List<Interface>> still works and becomes List<? extends List<? extends Interface>>.

It will also unnecessarily do it for concrete types, which should be harmless. e.g., List<List<ConcreteType>> becomes List<? extends List<ConcreteType>>.

canUseWildcardType = true
}
}

Expand Down Expand Up @@ -275,7 +279,7 @@ class TypeUtils(
return NodeTraverser().postOrder(visitor, fieldType) as TypeName
}

private fun isFieldTypeAnInterface(fieldDefinitionType: TypeName): Boolean =
private fun isFieldTypeAnInterface(fieldDefinitionType: Type<*>): Boolean =
document
.getDefinitionsOfType(InterfaceTypeDefinition::class.java)
.any { node -> node.name == findInnerType(fieldDefinitionType).name }
Expand Down
38 changes: 30 additions & 8 deletions graphql-dgs-codegen-core/src/test/kotlin/com/netflix/graphql/dgs/codegen/CodeGenTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -993,6 +993,12 @@ class CodeGenTest {
| Pet getMother();
|
| Pet getFather();
|
| List<? extends Pet> getParents();
|
| List<? extends List<? extends Pet>> getFriends();
|
| List<? extends Pet> getSiblings();
|}
|
""".trimMargin(),
Expand Down Expand Up @@ -3393,6 +3399,7 @@ class CodeGenTest {
|import com.netflix.graphql.dgs.codegen.tests.generated.Generated;
|import java.lang.Integer;
|import java.lang.String;
|import java.util.List;
|
|@Generated
|@JsonTypeInfo(
Expand All @@ -3414,6 +3421,8 @@ class CodeGenTest {
| void setAge(Integer age);
|
| Employee getBoss();
|
| List<? extends Employee> getTeam();
|}
|
""".trimMargin(),
Expand Down Expand Up @@ -3480,9 +3489,9 @@ class CodeGenTest {
|
| void setAge(Integer age);
|
| List<Person> getParents();
| List<? extends Person> getParents();
|
| void setParents(List<Person> parents);
| void setParents(List<? extends Person> parents);
|
| Person getFriend();
|
Expand Down Expand Up @@ -3520,9 +3529,9 @@ class CodeGenTest {
|
| void setAge(Integer age);
|
| List<Person> getParents();
| List<? extends Person> getParents();
|
| void setParents(List<Person> parents);
| void setParents(List<? extends Person> parents);
|
| Person getFriend();
|
Expand Down Expand Up @@ -3993,14 +4002,27 @@ class CodeGenTest {
|
| void setName(String name);
|
| List<Pet> getFriends();
| List<? extends Pet> getFriends();
|
| void setFriends(List<Pet> friends);
| void setFriends(List<? extends Pet> friends);

@ryanflegel ryanflegel Aug 27, 2026

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This demonstrates how interface-setters also have wildcards. This is more flexible for the Java compiler, but may theoretically lead to runtime errors. e.g., if a concrete type only supported a specific subtype of Pet.

Note that this is consistent with the existing generateInterfaces behaviour, but I wanted to point it out.

|}
|
""".trimMargin(),
)

assertThat(dataTypes[0].toString()).contains(
"""
| public List<? extends Pet> getFriends() {
| return friends;
| }
|
| public void setFriends(List<? extends Pet> friends) {
| this.friends = friends;
| }
|
""".trimMargin(),
)

assertCompilesJava(codeGenResult)
}

Expand Down Expand Up @@ -4059,7 +4081,7 @@ class CodeGenTest {
|
| Integer getAge();
|
| List<Person> getParents();
| List<? extends Person> getParents();
|
| Person getFriend();
|}
Expand Down Expand Up @@ -4091,7 +4113,7 @@ class CodeGenTest {
|
| Integer getAge();
|
| List<Person> getParents();
| List<? extends Person> getParents();
|
| Person getFriend();
|}
Expand Down
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