Add a __typename method on projections for selection. (#685)

* Use concrete types for JsonSubType annotations on interfaces if available.

* Add a __typename() method to select on projections.

Author: srinivasankavitha

graphql-dgs-codegen-core/src/main/kotlin/com/netflix/graphql/dgs/codegen/generators/java/ClientApiGenerator.kt

@@ -256,6 +256,20 @@ class ClientApiGenerator(private val config: CodeGenConfig, private val document
                     .build()
             )
 
+        val typeVariable = TypeVariableName.get("$clazzName<PARENT, ROOT>")
+        javaType.addMethod(
+            MethodSpec.methodBuilder(TypeNameMetaFieldDef.name)
+                .returns(typeVariable)
+                .addCode(
+                    """
+                        |getFields().put("${TypeNameMetaFieldDef.name}", null);
+                        |return this;
+                    """.trimMargin()
+                )
+                .addModifiers(Modifier.PUBLIC)
+                .build()
+        )
+
         if (generatedClasses.contains(clazzName)) return CodeGenResult() else generatedClasses.add(clazzName)
 
         val fieldDefinitions = type.fieldDefinitions() + document.definitions.filterIsInstance<ObjectTypeExtensionDefinition>().filter { it.name == type.name }.flatMap { it.fieldDefinitions }
@@ -534,6 +548,21 @@ class ClientApiGenerator(private val config: CodeGenConfig, private val document
                     .build()
             )
 
+        // add a method for setting the __typename
+        val typeVariable = TypeVariableName.get("$clazzName<PARENT, ROOT>")
+        javaType.addMethod(
+            MethodSpec.methodBuilder(TypeNameMetaFieldDef.name)
+                .returns(typeVariable)
+                .addCode(
+                    """
+                        |getFields().put("${TypeNameMetaFieldDef.name}", null);
+                        |return this;
+                    """.trimMargin()
+                )
+                .addModifiers(Modifier.PUBLIC)
+                .build()
+        )
+
         val fieldDefinitions = type.fieldDefinitions() +
             document.definitions
                 .filterIsInstance<ObjectTypeExtensionDefinition>()

graphql-dgs-codegen-core/src/test/kotlin/com/netflix/graphql/dgs/codegen/clientapi/ClientApiGenFragmentTest.kt

@@ -61,6 +61,7 @@ class ClientApiGenFragmentTest {
         assertThat(codeGenResult.clientProjections.size).isEqualTo(3)
         assertThat(codeGenResult.clientProjections[0].typeSpec.name).isEqualTo("SearchProjectionRoot")
         assertThat(codeGenResult.clientProjections[0].typeSpec.methodSpecs).extracting("name").contains("title")
+        assertThat(codeGenResult.clientProjections[0].typeSpec.methodSpecs).extracting("name").contains("__typename")
         assertThat(codeGenResult.clientProjections[1].typeSpec.name).isEqualTo("MovieFragmentProjection")
         assertThat(codeGenResult.clientProjections[1].typeSpec.methodSpecs).extracting("name").contains("duration")
         assertThat(codeGenResult.clientProjections[1].typeSpec.methodSpecs).extracting("name").contains("title")
@@ -114,8 +115,10 @@ class ClientApiGenFragmentTest {
 
         assertThat(codeGenResult.clientProjections.size).isEqualTo(4)
         assertThat(codeGenResult.clientProjections[0].typeSpec.name).isEqualTo("SearchProjectionRoot")
+        assertThat(codeGenResult.clientProjections[0].typeSpec.methodSpecs).extracting("name").contains("__typename")
         assertThat(codeGenResult.clientProjections[1].typeSpec.name).isEqualTo("ShowProjection")
         assertThat(codeGenResult.clientProjections[1].typeSpec.methodSpecs).extracting("name").contains("title")
+        assertThat(codeGenResult.clientProjections[1].typeSpec.methodSpecs).extracting("name").contains("__typename")
         assertThat(codeGenResult.clientProjections[2].typeSpec.name).isEqualTo("MovieFragmentProjection")
         assertThat(codeGenResult.clientProjections[2].typeSpec.methodSpecs).extracting("name").contains("duration")
         assertThat(codeGenResult.clientProjections[2].typeSpec.methodSpecs).extracting("name").contains("title")
@@ -160,6 +163,7 @@ class ClientApiGenFragmentTest {
 
         assertThat(codeGenResult.clientProjections.size).isEqualTo(3)
         assertThat(codeGenResult.clientProjections[0].typeSpec.name).isEqualTo("SearchProjectionRoot")
+        assertThat(codeGenResult.clientProjections[0].typeSpec.methodSpecs).extracting("name").contains("__typename")
         assertThat(codeGenResult.clientProjections[0].typeSpec.methodSpecs).extracting("name").contains("onMovie")
         assertThat(codeGenResult.clientProjections[0].typeSpec.methodSpecs).extracting("name").contains("onActor")
         assertThat(codeGenResult.clientProjections[1].typeSpec.name).isEqualTo("MovieFragmentProjection")

graphql-dgs-codegen-core/src/test/kotlin/com/netflix/graphql/dgs/codegen/clientapi/ClientApiGenProjectionTest.kt

@@ -367,8 +367,8 @@ class ClientApiGenProjectionTest {
         val projections = codeGenResult.clientProjections
         assertThat(projections.size).isEqualTo(1)
         assertThat(projections[0].typeSpec.name).isEqualTo("PeopleProjectionRoot")
-        assertThat(projections[0].typeSpec.methodSpecs.size).isEqualTo(3)
-        assertThat(projections[0].typeSpec.methodSpecs).extracting("name").contains("name", "email")
+        assertThat(projections[0].typeSpec.methodSpecs.size).isEqualTo(4)
+        assertThat(projections[0].typeSpec.methodSpecs).extracting("name").contains("name", "email", "__typename")
 
         assertCompilesJava(codeGenResult)
     }
@@ -404,8 +404,8 @@ class ClientApiGenProjectionTest {
         val projections = codeGenResult.clientProjections
         assertThat(projections.size).isEqualTo(2)
         assertThat(projections[1].typeSpec.name).isEqualTo("MovieProjection")
-        assertThat(projections[1].typeSpec.methodSpecs.size).isEqualTo(3)
-        assertThat(projections[1].typeSpec.methodSpecs).extracting("name").contains("title", "director", "<init>")
+        assertThat(projections[1].typeSpec.methodSpecs.size).isEqualTo(4)
+        assertThat(projections[1].typeSpec.methodSpecs).extracting("name").contains("title", "director", "<init>", "__typename")
 
         assertCompilesJava(codeGenResult)
     }
@@ -441,7 +441,7 @@ class ClientApiGenProjectionTest {
         val projections = codeGenResult.clientProjections
         assertThat(projections.size).isEqualTo(2)
         assertThat(projections[1].typeSpec.name).isEqualTo("MovieProjection")
-        assertThat(projections[1].typeSpec.methodSpecs.size).isEqualTo(3)
+        assertThat(projections[1].typeSpec.methodSpecs.size).isEqualTo(4)
         assertThat(projections[1].typeSpec.methodSpecs).extracting("name").contains("title", "director", "<init>")
 
         assertCompilesJava(codeGenResult)
@@ -716,7 +716,7 @@ class ClientApiGenProjectionTest {
         ).generate()
 
         val methodSpecs = codeGenResult.clientProjections[0].typeSpec.methodSpecs
-        assertThat(methodSpecs.size).isEqualTo(3)
+        assertThat(methodSpecs.size).isEqualTo(4)
         val methodWithArgs = methodSpecs.find { it.parameters.size > 0 && it.name == "actors" }
             ?: fail("Expected method not found")
         assertThat(methodWithArgs.parameters[0].name).isEqualTo("leadCharactersOnly")

graphql-dgs-codegen-core/src/test/kotlin/com/netflix/graphql/dgs/codegen/clientapi/ClientApiGenQueryTest.kt

@@ -441,11 +441,11 @@ class ClientApiGenQueryTest {
         assertThat(codeGenResult.javaQueryTypes[0].typeSpec.name).isEqualTo("SearchGraphQLQuery")
         assertThat(codeGenResult.clientProjections.size).isEqualTo(3)
         assertThat(codeGenResult.clientProjections[0].typeSpec.name).isEqualTo("SearchProjectionRoot")
-        assertThat(codeGenResult.clientProjections[0].typeSpec.methodSpecs[1].name).isEqualTo("title")
+        assertThat(codeGenResult.clientProjections[0].typeSpec.methodSpecs[2].name).isEqualTo("title")
         assertThat(codeGenResult.clientProjections[1].typeSpec.name).isEqualTo("MovieFragmentProjection")
-        assertThat(codeGenResult.clientProjections[1].typeSpec.methodSpecs[2].name).isEqualTo("duration")
+        assertThat(codeGenResult.clientProjections[1].typeSpec.methodSpecs[3].name).isEqualTo("duration")
         assertThat(codeGenResult.clientProjections[2].typeSpec.name).isEqualTo("SeriesFragmentProjection")
-        assertThat(codeGenResult.clientProjections[2].typeSpec.methodSpecs[2].name).isEqualTo("episodes")
+        assertThat(codeGenResult.clientProjections[2].typeSpec.methodSpecs[3].name).isEqualTo("episodes")
 
         assertCompilesJava(
             codeGenResult.clientProjections + codeGenResult.javaQueryTypes + codeGenResult.javaEnumTypes + codeGenResult.javaDataTypes + codeGenResult.javaInterfaces