feat(codegen): refactor field resolvers

Author: WipeAir

graphql-kotlin-toolkit-codegen/src/main/kotlin/com/auritylab/graphql/kotlin/toolkit/codegen/generator/fieldResolver/AbstractFieldResolverGenerator.kt

@@ -33,16 +33,38 @@ internal abstract class AbstractFieldResolverGenerator(
     kotlinTypeMapper: KotlinTypeMapper,
     generatedMapper: GeneratedMapper
 ) : AbstractClassGenerator(options, kotlinTypeMapper, generatedMapper) {
-    protected val fieldKotlinType = getKotlinType(field.type)
-
+    /**
+     * Describes the [ClassName] for the actual class which describes the field resolver.
+     * This will be used on the [TypeSpec] of [buildFieldResolverClass].
+     */
     override val fileClassName: ClassName = generatedMapper.getGeneratedFieldResolverClassName(container, field)
+
+    /**
+     * Describes the [TypeName] for the return type of the field.
+     */
+    protected val fieldTypeName = getKotlinType(field.type)
+
+    /**
+     * Describes the actual return [TypeName] which will be returned by the "graphql.schema.DataFetcher", which will
+     * be implemented, by this field resolver interface. This can be overridden by subclasses to adjust the
+     */
+    protected open val returnTypeName: TypeName = fieldTypeName
+
     protected val dataFetchingEnvironmentClassName = ClassName("graphql.schema", "DataFetchingEnvironment")
-    protected val dataFetcherClassName = ClassName("graphql.schema", "DataFetcher").parameterizedBy(fieldKotlinType)
+
+    /**
+     * Describes the "graphql.schema.DataFetcher" [TypeName] which is parameterized by the [returnTypeName].
+     */
+    protected val parameterizedDataFetcherTypeName: TypeName
+        get() = ClassName("graphql.schema", "DataFetcher").parameterizedBy(returnTypeName)
+
     protected val contextClassName = options.globalContext?.let { ClassName.bestGuess(it) } ?: ANY
 
     override fun build(builder: FileSpec.Builder) {
         val typeBuilder = TypeSpec.interfaceBuilder(fileClassName)
 
+        typeBuilder.addSuperinterface(parameterizedDataFetcherTypeName)
+
         // Call the build methods with the type builder.
         buildFieldResolverClass(typeBuilder)
 
@@ -58,7 +80,8 @@ internal abstract class AbstractFieldResolverGenerator(
     }
 
     /**
-     * Will build the [TypeSpec] which represents the field resolver itself.
+     * Will continue the building of the resolver. Some types, functions, etc. have already been.
+     * This shall only be used for additionally required types, functions, etc.
      */
     protected abstract fun buildFieldResolverClass(builder: TypeSpec.Builder)
 
@@ -79,11 +102,12 @@ internal abstract class AbstractFieldResolverGenerator(
                 .getImplementers(container)
                 .map { getKotlinType(it) }
 
+            // Fetch the first type to have a reference type to check against.
             val firstType = implementersTypes.first()
-            if (implementersTypes.all { it == firstType })
-                firstType
-            else
-                ANY
+
+            // If all implementers have the same type as the first, the reference type can be returned.
+            if (implementersTypes.all { it == firstType }) firstType
+            else ANY
         } else throw UnsupportedOperationException()
 
     /**

graphql-kotlin-toolkit-codegen/src/main/kotlin/com/auritylab/graphql/kotlin/toolkit/codegen/generator/fieldResolver/FieldResolverGenerator.kt

@@ -34,15 +34,14 @@ internal class FieldResolverGenerator(
 ) {
     override fun buildFieldResolverClass(builder: TypeSpec.Builder) {
         builder
-            .addSuperinterface(dataFetcherClassName)
             .addType(environmentTypeSpec)
 
         builder.addFunction(
             FunSpec.builder("resolve")
                 .addModifiers(KModifier.ABSTRACT)
                 .addParameters(field.arguments.map { ParameterSpec(it.name, getKotlinType(it.type, it)) })
                 .addParameter("env", generatedMapper.getFieldResolverEnvironment(container, field))
-                .returns(fieldKotlinType).build()
+                .returns(fieldTypeName).build()
         )
 
         builder.addFunction(FunSpec.builder("get")

graphql-kotlin-toolkit-codegen/src/main/kotlin/com/auritylab/graphql/kotlin/toolkit/codegen/generator/fieldResolver/PaginationFieldResolverGenerator.kt

@@ -47,23 +47,16 @@ internal class PaginationFieldResolverGenerator(
     private val unwrappedReturnKotlinType = getKotlinType(unwrappedReturnType)
     private val resolveReturnType: TypeName = getKotlinType(field.type, null, LIST)
 
+    override val returnTypeName: TypeName = generatedMapper
+        .getPaginationConnectionClassName()
+        .parameterizedBy(unwrappedReturnKotlinType)
+
     override fun buildFieldResolverClass(builder: TypeSpec.Builder) {
         builder
             .addType(environmentTypeSpec)
             .addType(resultHolderTypeSpec)
             .addFunction(resolveCursorFunSpec)
             .addFunction(resultFunSpec)
-            .addFunction(buildEdgeFunSpec)
-            .addFunction(buildConnectionFunSpec)
-            .addFunction(buildPageInfoFunSpec)
-            .addSuperinterface(
-                ClassName(
-                    "graphql.schema",
-                    "DataFetcher"
-                ).parameterizedBy(
-                    generatedMapper.getPaginationConnectionClassName().parameterizedBy(unwrappedReturnKotlinType)
-                )
-            )
 
         builder.addFunction(
             FunSpec.builder("resolve")
@@ -95,9 +88,12 @@ internal class PaginationFieldResolverGenerator(
                 )
                 getFunSpec.addStatement("val result = resolve(${resolveArgs}env = internalEnv)")
 
-                getFunSpec.addStatement("val edges = result.data.map { _buildEdge(it, internalEnv) }")
-                getFunSpec.addStatement("val pageInfo = _buildPageInfo(result.hasNextPage, result.hasPreviousPage, edges.first().cursor, edges.last().cursor)")
-                getFunSpec.addStatement("return _buildConnection(edges, pageInfo)")
+                getFunSpec.addStatement("val edges = result.data.map { %T(it, resolveCursor(it, internalEnv)) }", generatedMapper.getPaginationEdgeClassName())
+                getFunSpec.addStatement(
+                    "val pageInfo = %T(result.hasNextPage, result.hasPreviousPage, edges.first().cursor, edges.last().cursor)",
+                    generatedMapper.getPaginationPageInfoClassName()
+                )
+                getFunSpec.addStatement("return %T(edges, pageInfo)", generatedMapper.getPaginationConnectionClassName())
             }
             .build())
     }
@@ -174,43 +170,4 @@ internal class PaginationFieldResolverGenerator(
         .addProperty(PropertySpec.builder("hasPreviousPage", BOOLEAN).initializer("hasPreviousPage").build())
         .addProperty(PropertySpec.builder("hasNextPage", BOOLEAN).initializer("hasNextPage").build())
         .build()
-
-    private val buildEdgeFunSpec = FunSpec.builder("_buildEdge")
-        .addModifiers(KModifier.PRIVATE)
-        .addParameter("data", unwrappedReturnKotlinType)
-        .addParameter("env", generatedMapper.getFieldResolverEnvironment(container, field))
-        .returns(generatedMapper.getPaginationEdgeClassName().parameterizedBy(unwrappedReturnKotlinType))
-        .addCode(
-            CodeBlock.of(
-                "return %T(data, resolveCursor(data, env))",
-                generatedMapper.getPaginationEdgeClassName()
-            )
-        )
-        .build()
-
-    private val buildConnectionFunSpec = FunSpec.builder("_buildConnection")
-        .addModifiers(KModifier.PRIVATE)
-        .addParameter(
-            "edges",
-            LIST.parameterizedBy(
-                generatedMapper.getPaginationEdgeClassName().parameterizedBy(unwrappedReturnKotlinType)
-            )
-        )
-        .addParameter("pageInfo", generatedMapper.getPaginationPageInfoClassName())
-        .returns(generatedMapper.getPaginationConnectionClassName().parameterizedBy(unwrappedReturnKotlinType))
-        .addCode(CodeBlock.of("return %T(edges, pageInfo)", generatedMapper.getPaginationConnectionClassName()))
-        .build()
-
-    private val buildPageInfoFunSpec = FunSpec.builder("_buildPageInfo")
-        .addModifiers(KModifier.PRIVATE)
-        .addParameter("hasNextPage", BOOLEAN)
-        .addParameter("hasPreviousPage", BOOLEAN)
-        .addParameter("startCursor", STRING)
-        .addParameter("endCursor", STRING)
-        .returns(generatedMapper.getPaginationPageInfoClassName())
-        .addStatement(
-            "return %T(hasNextPage, hasPreviousPage, startCursor, endCursor)",
-            generatedMapper.getPaginationPageInfoClassName()
-        )
-        .build()
 }