#1102 Add support for Auto forging of Enum properties

processor/src/main/java/org/mapstruct/ap/internal/model/AbstractBaseBuilder.java

@@ -21,6 +21,7 @@ package org.mapstruct.ap.internal.model;
 import org.mapstruct.ap.internal.model.assignment.Assignment;
 import org.mapstruct.ap.internal.model.common.ParameterBinding;
 import org.mapstruct.ap.internal.model.source.ForgedMethod;
+import org.mapstruct.ap.internal.model.source.MappingMethodUtils;
 import org.mapstruct.ap.internal.model.source.Method;
 
 /**
@@ -55,11 +56,21 @@ class AbstractBaseBuilder<B extends AbstractBaseBuilder<B>> {
      *
      * @return See above
      */
-    Assignment createForgedBeanAssignment(SourceRHS sourceRHS, ForgedMethod forgedMethod) {
+    Assignment createForgedAssignment(SourceRHS sourceRHS, ForgedMethod forgedMethod) {
-        BeanMappingMethod forgedMappingMethod = new BeanMappingMethod.Builder()
+        MappingMethod forgedMappingMethod;
-            .forgedMethod( forgedMethod )
+        if ( MappingMethodUtils.isEnumMapping( forgedMethod ) ) {
-            .mappingContext( ctx )
+            forgedMappingMethod = new ValueMappingMethod.Builder()
-            .build();
+                .method( forgedMethod )
+                .valueMappings( forgedMethod.getMappingOptions().getValueMappings() )
+                .mappingContext( ctx )
+                .build();
+        }
+        else {
+            forgedMappingMethod = new BeanMappingMethod.Builder()
+                .forgedMethod( forgedMethod )
+                .mappingContext( ctx )
+                .build();
+        }
 
         return createForgedAssignment( sourceRHS, forgedMethod, forgedMappingMethod );
     }

processor/src/main/java/org/mapstruct/ap/internal/model/AbstractMappingMethodBuilder.java

@@ -73,7 +73,7 @@ public abstract class AbstractMappingMethodBuilder<B extends AbstractMappingMeth
             true
         );
 
-        return createForgedBeanAssignment( sourceRHS, forgedMethod );
+        return createForgedAssignment( sourceRHS, forgedMethod );
     }
 
     private String getName(Type sourceType, Type targetType) {

processor/src/main/java/org/mapstruct/ap/internal/model/PropertyMapping.java

@@ -634,7 +634,8 @@ public class PropertyMapping extends ModelElement {
             // there's only one case for forging a method with mapping options: nested target properties.
             // They should forge an update method only if we set the forceUpdateMethod. This is set to true,
             // because we are forging a Mapping for a method with multiple source parameters.
-            if ( method.isUpdateMethod() || forceUpdateMethod ) {
+            // If the target type is enum, then we can't create an update method
+            if ( !targetType.isEnumType() && ( method.isUpdateMethod() || forceUpdateMethod ) ) {
                 parameters.add( Parameter.forForgedMappingTarget( targetType ) );
                 returnType = ctx.getTypeFactory().createVoidType();
             }
@@ -653,7 +654,7 @@ public class PropertyMapping extends ModelElement {
                 forgeMethodWithMappingOptions,
                 forgedNamedBased
             );
-            return createForgedBeanAssignment( sourceRHS, forgedMethod );
+            return createForgedAssignment( sourceRHS, forgedMethod );
         }
 
         private ForgedMethodHistory getForgedMethodHistory(SourceRHS sourceRHS) {

processor/src/main/java/org/mapstruct/ap/internal/model/ValueMappingMethod.java

@@ -28,9 +28,10 @@ import java.util.Set;
 import javax.lang.model.type.TypeMirror;
 
 import org.mapstruct.ap.internal.model.common.Parameter;
+import org.mapstruct.ap.internal.model.source.ForgedMethod;
+import org.mapstruct.ap.internal.model.source.ForgedMethodHistory;
 import org.mapstruct.ap.internal.model.source.Method;
 import org.mapstruct.ap.internal.model.source.SelectionParameters;
-import org.mapstruct.ap.internal.model.source.SourceMethod;
 import org.mapstruct.ap.internal.model.source.ValueMapping;
 import org.mapstruct.ap.internal.prism.BeanMappingPrism;
 import org.mapstruct.ap.internal.prism.MappingConstantsPrism;
@@ -49,10 +50,11 @@ public class ValueMappingMethod extends MappingMethod {
     private final String defaultTarget;
     private final String nullTarget;
     private final boolean throwIllegalArgumentException;
+    private final boolean overridden;
 
     public static class Builder {
 
-        private SourceMethod method;
+        private Method method;
         private MappingBuilderContext ctx;
         private final List<ValueMapping> trueValueMappings = new ArrayList<ValueMapping>();
         private ValueMapping defaultTargetValue = null;
@@ -64,7 +66,7 @@ public class ValueMappingMethod extends MappingMethod {
             return this;
         }
 
-        public Builder souceMethod(SourceMethod sourceMethod) {
+        public Builder method(Method sourceMethod) {
             this.method = sourceMethod;
             return this;
         }
@@ -128,7 +130,7 @@ public class ValueMappingMethod extends MappingMethod {
                 throwIllegalArgumentException, beforeMappingMethods, afterMappingMethods );
         }
 
-        private List<MappingEntry> enumToEnumMapping(SourceMethod method) {
+        private List<MappingEntry> enumToEnumMapping(Method method) {
 
             List<MappingEntry> mappings = new ArrayList<MappingEntry>();
             List<String> unmappedSourceConstants
@@ -161,10 +163,20 @@ public class ValueMappingMethod extends MappingMethod {
                 }
 
                 if ( defaultTargetValue == null && !unmappedSourceConstants.isEmpty() ) {
+                    String sourceErrorMessage = "source";
+                    String targetErrorMessage = "target";
+                    if ( method instanceof ForgedMethod && ( (ForgedMethod) method ).getHistory() != null ) {
+                        ForgedMethodHistory history = ( (ForgedMethod) method ).getHistory();
+                        sourceErrorMessage = history.createSourcePropertyErrorMessage();
+                        targetErrorMessage =
+                            "\"" + history.getTargetType().toString() + " " + history.createTargetPropertyName() + "\"";
+                    }
                     // all sources should now be matched, there's no default to fall back to, so if sources remain,
                     // we have an issue.
                     ctx.getMessager().printMessage( method.getExecutable(),
                         Message.VALUE_MAPPING_UNMAPPED_SOURCES,
+                        sourceErrorMessage,
+                        targetErrorMessage,
                         Strings.join( unmappedSourceConstants, ", " )
                     );
 
@@ -173,7 +185,7 @@ public class ValueMappingMethod extends MappingMethod {
             return mappings;
         }
 
-        private SelectionParameters getSelectionParameters(SourceMethod method) {
+        private SelectionParameters getSelectionParameters(Method method) {
             BeanMappingPrism beanMappingPrism = BeanMappingPrism.getInstanceOn( method.getExecutable() );
             if ( beanMappingPrism != null ) {
                 List<TypeMirror> qualifiers = beanMappingPrism.qualifiedBy();
@@ -184,7 +196,7 @@ public class ValueMappingMethod extends MappingMethod {
             return null;
         }
 
-        private boolean reportErrorIfMappedEnumConstantsDontExist(SourceMethod method) {
+        private boolean reportErrorIfMappedEnumConstantsDontExist(Method method) {
             List<String> sourceEnumConstants = first( method.getSourceParameters() ).getType().getEnumConstants();
             List<String> targetEnumConstants = method.getReturnType().getEnumConstants();
 
@@ -251,6 +263,7 @@ public class ValueMappingMethod extends MappingMethod {
         this.nullTarget = nullTarget;
         this.defaultTarget = defaultTarget;
         this.throwIllegalArgumentException = throwIllegalArgumentException;
+        this.overridden = method.overridesMethod();
     }
 
     public List<MappingEntry> getValueMappings() {
@@ -273,6 +286,10 @@ public class ValueMappingMethod extends MappingMethod {
         return first( getParameters() );
     }
 
+    public boolean isOverridden() {
+        return overridden;
+    }
+
     public static class MappingEntry {
         private final String source;
         private final String target;

processor/src/main/java/org/mapstruct/ap/internal/model/source/MappingMethodUtils.java

@@ -0,0 +1,48 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.internal.model.source;
+
+import static org.mapstruct.ap.internal.util.Collections.first;
+
+/**
+ * @author Filip Hrisafov
+ */
+public final class MappingMethodUtils {
+
+    /**
+     * Hide default constructor.
+     */
+    private MappingMethodUtils() {
+    }
+
+
+    /**
+     * Checks if the provided {@code method} is for enum mapping. A Method is an Enum Mapping method when the
+     * source parameter and result type are enum types.
+     *
+     * @param method to check
+     *
+     * @return {@code true} if the method is for enum mapping, {@code false} otherwise
+     */
+    public static boolean isEnumMapping(Method method) {
+        return method.getSourceParameters().size() == 1
+            && first( method.getSourceParameters() ).getType().isEnumType()
+            && method.getResultType().isEnumType();
+    }
+}

processor/src/main/java/org/mapstruct/ap/internal/model/source/SourceMethod.java

@@ -381,9 +381,7 @@ public class SourceMethod implements Method {
 
     public boolean isEnumMapping() {
         if ( isEnumMapping == null ) {
-            isEnumMapping = getSourceParameters().size() == 1
+            isEnumMapping = MappingMethodUtils.isEnumMapping( this );
-                && first( getSourceParameters() ).getType().isEnumType()
-                && getResultType().isEnumType();
         }
         return isEnumMapping;
     }

processor/src/main/java/org/mapstruct/ap/internal/processor/MapperCreationProcessor.java

@@ -317,7 +317,7 @@ public class MapperCreationProcessor implements ModelElementProcessor<List<Sourc
                 // prefer value mappings over enum mapping
                 ValueMappingMethod valueMappingMethod = new ValueMappingMethod.Builder()
                     .mappingContext( mappingContext )
-                    .souceMethod( method )
+                    .method( method )
                     .valueMappings( mappingOptions.getValueMappings() )
                     .build();
                 mappingMethods.add( valueMappingMethod );

processor/src/main/java/org/mapstruct/ap/internal/util/Message.java

@@ -118,7 +118,7 @@ public enum Message {
 
     VALUEMAPPING_DUPLICATE_SOURCE( "Source value mapping: \"%s\" cannot be mapped more than once." ),
     VALUEMAPPING_ANY_AREADY_DEFINED( "Source = \"<ANY_REMAINING>\" or \"<ANY_UNMAPPED>\" can only be used once." ),
-    VALUE_MAPPING_UNMAPPED_SOURCES( "The following constants from the source enum have no corresponding constant in the target enum and must be be mapped via adding additional mappings: %s." ),
+    VALUE_MAPPING_UNMAPPED_SOURCES( "The following constants from the %s enum have no corresponding constant in the %s enum and must be be mapped via adding additional mappings: %s." ),
     VALUEMAPPING_NON_EXISTING_CONSTANT( "Constant %s doesn't exist in enum type %s." );
 
     // CHECKSTYLE:ON

processor/src/main/resources/org/mapstruct/ap/internal/model/ValueMappingMethod.ftl

@@ -19,8 +19,8 @@
      limitations under the License.
 
 -->
-@Override
+<#if overridden>@Override</#if>
-public <@includeModel object=returnType/> ${name}(<@includeModel object=sourceParameter/>) {
+<#lt>${accessibility.keyword} <@includeModel object=returnType/> ${name}(<@includeModel object=sourceParameter/>) {
     <#list beforeMappingReferencesWithoutMappingTarget as callback>
         <@includeModel object=callback targetBeanName=resultName targetType=resultType/>
         <#if !callback_has_next>

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/DottedErrorMessageTest.java

@@ -31,10 +31,12 @@ import org.mapstruct.ap.test.nestedbeans.erroneous.Cat;
 import org.mapstruct.ap.test.nestedbeans.erroneous.CatDto;
 import org.mapstruct.ap.test.nestedbeans.erroneous.Info;
 import org.mapstruct.ap.test.nestedbeans.erroneous.InfoDto;
+import org.mapstruct.ap.test.nestedbeans.erroneous.RoofTypeMapper;
 import org.mapstruct.ap.test.nestedbeans.erroneous.UnmappableCollectionElementPropertyMapper;
 import org.mapstruct.ap.test.nestedbeans.erroneous.UnmappableDeepListMapper;
 import org.mapstruct.ap.test.nestedbeans.erroneous.UnmappableDeepMapKeyMapper;
 import org.mapstruct.ap.test.nestedbeans.erroneous.UnmappableDeepMapValueMapper;
+import org.mapstruct.ap.test.nestedbeans.erroneous.UnmappableEnumMapper;
 import org.mapstruct.ap.test.nestedbeans.erroneous.UnmappableValuePropertyMapper;
 import org.mapstruct.ap.test.nestedbeans.erroneous.UserDto;
 import org.mapstruct.ap.test.nestedbeans.erroneous.User;
@@ -42,11 +44,13 @@ import org.mapstruct.ap.test.nestedbeans.erroneous.WheelDto;
 import org.mapstruct.ap.test.nestedbeans.erroneous.Wheel;
 import org.mapstruct.ap.test.nestedbeans.erroneous.Car;
 import org.mapstruct.ap.test.nestedbeans.erroneous.CarDto;
+import org.mapstruct.ap.test.nestedbeans.erroneous.ExternalRoofType;
 import org.mapstruct.ap.test.nestedbeans.erroneous.House;
 import org.mapstruct.ap.test.nestedbeans.erroneous.HouseDto;
 import org.mapstruct.ap.test.nestedbeans.erroneous.Color;
 import org.mapstruct.ap.test.nestedbeans.erroneous.ColorDto;
 import org.mapstruct.ap.test.nestedbeans.erroneous.Roof;
+import org.mapstruct.ap.test.nestedbeans.erroneous.RoofType;
 import org.mapstruct.ap.test.nestedbeans.erroneous.RoofDto;
 import org.mapstruct.ap.test.nestedbeans.erroneous.UnmappableDeepNestingMapper;
 import org.mapstruct.ap.test.nestedbeans.erroneous.Word;
@@ -60,6 +64,7 @@ import org.mapstruct.ap.testutil.runner.AnnotationProcessorTestRunner;
 @WithClasses({
     Car.class, CarDto.class, Color.class, ColorDto.class,
     House.class, HouseDto.class, Roof.class, RoofDto.class,
+    RoofType.class, ExternalRoofType.class, RoofTypeMapper.class,
     User.class, UserDto.class, Wheel.class, WheelDto.class,
     Dictionary.class, DictionaryDto.class, Word.class, WordDto.class,
     ForeignWord.class, ForeignWordDto.class,
@@ -183,4 +188,23 @@ public class DottedErrorMessageTest {
     )
     public void testMapValueProperty() {
     }
+
+    @Test
+    @WithClasses({
+        UnmappableEnumMapper.class
+    })
+    @ExpectedCompilationOutcome(
+        value = CompilationResult.FAILED,
+        diagnostics = {
+            @Diagnostic(type = UnmappableEnumMapper.class,
+                kind = javax.tools.Diagnostic.Kind.ERROR,
+                line = 26,
+                messageRegExp = "The following constants from the property \".*RoofType house\\.roof\\.type\" enum " +
+                    "have no corresponding constant in the \".*ExternalRoofType house\\.roof\\.type\" enum and must " +
+                    "be be mapped via adding additional mappings: NORMAL\\."
+            )
+        }
+    )
+    public void testMapEnumProperty() {
+    }
 }

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/ExternalRoofType.java

@@ -0,0 +1,28 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.nestedbeans;
+
+
+/**
+ * @author Filip Hrisafov
+ */
+public enum ExternalRoofType {
+
+    OPEN, BOX, GAMBREL, STANDARD, NORMAL
+}

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/NestedSimpleBeansMappingTest.java

@@ -18,17 +18,28 @@
  */
 package org.mapstruct.ap.test.nestedbeans;
 
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import org.assertj.core.groups.Tuple;
+import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mapstruct.ap.testutil.WithClasses;
 import org.mapstruct.ap.testutil.runner.AnnotationProcessorTestRunner;
+import org.mapstruct.ap.testutil.runner.GeneratedSource;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.tuple;
 
 @WithClasses({
     User.class, UserDto.class, Car.class, CarDto.class, House.class, HouseDto.class,
     Wheel.class, WheelDto.class,
     Roof.class, RoofDto.class,
+    RoofType.class, ExternalRoofType.class,
     org.mapstruct.ap.test.nestedbeans.other.CarDto.class,
     org.mapstruct.ap.test.nestedbeans.other.UserDto.class,
     org.mapstruct.ap.test.nestedbeans.other.HouseDto.class,
@@ -41,6 +52,59 @@ import static org.assertj.core.api.Assertions.assertThat;
 @RunWith(AnnotationProcessorTestRunner.class)
 public class NestedSimpleBeansMappingTest {
 
+    @Rule
+    public final GeneratedSource generatedSource = new GeneratedSource().addComparisonToFixtureFor(
+        UserDtoMapperClassic.class,
+        UserDtoMapperSmart.class,
+        UserDtoUpdateMapperSmart.class
+    );
+
+    /**
+     * Extracts all non synthetic declared fields from a class. This is needed, because jacoco adds a synthetic field
+     * to the classes and also assertj does not support testing that all fields are exactly there.
+     * This will be needed until <a href="https://github.com/joel-costigliola/assertj-core/issues/953">953</a> from
+     * assertj-core is implemented.
+     *
+     * @param clazz to extract from
+     *
+     * @return all the non synthetic declared fields
+     */
+    private static List<Field> extractAllFields(Class<?> clazz) {
+        List<Field> nonSyntheticFields = new ArrayList<Field>();
+        for ( Field field : clazz.getDeclaredFields() ) {
+            if ( !field.isSynthetic() ) {
+                nonSyntheticFields.add( field );
+            }
+        }
+
+        return nonSyntheticFields;
+    }
+
+    @Test
+    public void shouldHaveAllFields() throws Exception {
+        // If this test fails that means something new was added to the structure of the User/UserDto.
+        // Make sure that the other tests are also updated (the new field is asserted)
+        Object[] userFields = new String[] { "name", "car", "secondCar", "house" };
+        assertThat( extractAllFields( User.class ) ).extracting( "name" ).containsExactlyInAnyOrder( userFields );
+        assertThat( extractAllFields( UserDto.class ) ).extracting( "name" ).containsExactlyInAnyOrder( userFields );
+
+        Object[] carFields = new String[] { "name", "year", "wheels" };
+        assertThat( extractAllFields( Car.class ) ).extracting( "name" ).containsExactlyInAnyOrder( carFields );
+        assertThat( extractAllFields( CarDto.class ) ).extracting( "name" ).containsExactlyInAnyOrder( carFields );
+
+        Object[] wheelFields = new String[] { "front", "right" };
+        assertThat( extractAllFields( Wheel.class ) ).extracting( "name" ).containsExactlyInAnyOrder( wheelFields );
+        assertThat( extractAllFields( WheelDto.class ) ).extracting( "name" ).containsExactlyInAnyOrder( wheelFields );
+
+        Object[] houseFields = new String[] { "name", "year", "roof" };
+        assertThat( extractAllFields( House.class ) ).extracting( "name" ).containsExactlyInAnyOrder( houseFields );
+        assertThat( extractAllFields( HouseDto.class ) ).extracting( "name" ).containsExactlyInAnyOrder( houseFields );
+
+        Object[] roofFields = new String[] { "color", "type" };
+        assertThat( extractAllFields( Roof.class ) ).extracting( "name" ).containsExactlyInAnyOrder( roofFields );
+        assertThat( extractAllFields( RoofDto.class ) ).extracting( "name" ).containsExactlyInAnyOrder( roofFields );
+    }
+
     @Test
     public void shouldMapNestedBeans() {
 
@@ -49,11 +113,8 @@ public class NestedSimpleBeansMappingTest {
         UserDto classicMapping = UserDtoMapperClassic.INSTANCE.userToUserDto( user );
         UserDto smartMapping = UserDtoMapperSmart.INSTANCE.userToUserDto( user );
 
-        System.out.println( smartMapping );
+        assertUserDto( classicMapping, user );
-        System.out.println( classicMapping );
+        assertUserDto( smartMapping, user );
-
-        assertThat( smartMapping ).isNotNull();
-        assertThat( smartMapping ).isEqualTo( classicMapping );
     }
 
     @Test
@@ -67,15 +128,58 @@ public class NestedSimpleBeansMappingTest {
         smartMapping.setCar( new CarDto() );
         smartMapping.getCar().setName( "Toyota" );
 
-        // create a classic mapping and adapt expected result to Toyota
-        UserDto classicMapping = UserDtoMapperClassic.INSTANCE.userToUserDto( TestData.createUser() );
-        classicMapping.getCar().setName( "Toyota" );
-
         // action
         UserDtoUpdateMapperSmart.INSTANCE.userToUserDto( smartMapping, user );
 
         // result
-        assertThat( smartMapping ).isNotNull();
+        assertThat( smartMapping.getName() ).isEqualTo( user.getName() );
-        assertThat( smartMapping ).isEqualTo( classicMapping );
+        assertThat( smartMapping.getCar().getYear() ).isEqualTo( user.getCar().getYear() );
+        assertThat( smartMapping.getCar().getName() ).isEqualTo( "Toyota" );
+        assertThat( user.getCar().getName() ).isNull();
+        assertWheels( smartMapping.getCar().getWheels(), user.getCar().getWheels() );
+        assertCar( smartMapping.getSecondCar(), user.getSecondCar() );
+        assertHouse( smartMapping.getHouse(), user.getHouse() );
+    }
+
+    private static void assertUserDto(UserDto userDto, User user) {
+        assertThat( userDto ).isNotNull();
+        assertThat( userDto.getName() ).isEqualTo( user.getName() );
+        assertCar( userDto.getCar(), user.getCar() );
+        assertCar( userDto.getSecondCar(), user.getSecondCar() );
+        assertHouse( userDto.getHouse(), user.getHouse() );
+    }
+
+    private static void assertCar(CarDto carDto, Car car) {
+        if ( car == null ) {
+            assertThat( carDto ).isNull();
+        }
+        else {
+            assertThat( carDto.getName() ).isEqualTo( car.getName() );
+            assertThat( carDto.getYear() ).isEqualTo( car.getYear() );
+            assertWheels( carDto.getWheels(), car.getWheels() );
+        }
+    }
+
+    private static void assertWheels(List<WheelDto> wheelDtos, List<Wheel> wheels) {
+        List<Tuple> wheelTuples = wheels.stream().map( new Function<Wheel, Tuple>() {
+            @Override
+            public Tuple apply(Wheel wheel) {
+                return tuple( wheel.isFront(), wheel.isRight() );
+            }
+        } ).collect( Collectors.<Tuple>toList() );
+        assertThat( wheelDtos )
+            .extracting( "front", "right" )
+            .containsExactlyElementsOf( wheelTuples );
+    }
+
+    private static void assertHouse(HouseDto houseDto, House house) {
+        assertThat( houseDto.getName() ).isEqualTo( house.getName() );
+        assertThat( houseDto.getYear() ).isEqualTo( house.getYear() );
+        assertRoof( houseDto.getRoof(), house.getRoof() );
+    }
+
+    private static void assertRoof(RoofDto roofDto, Roof roof) {
+        assertThat( roofDto.getColor() ).isEqualTo( String.valueOf( roof.getColor() ) );
+        assertThat( roofDto.getType().name() ).isEqualTo( roof.getType().name() );
     }
 }

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/Roof.java

@@ -20,12 +20,14 @@ package org.mapstruct.ap.test.nestedbeans;
 
 public class Roof {
     private int color;
+    private RoofType type;
 
     public Roof() {
     }
 
-    public Roof(int color) {
+    public Roof(int color, RoofType type) {
         this.color = color;
+        this.type = type;
     }
 
     public int getColor() {
@@ -40,7 +42,16 @@ public class Roof {
     public String toString() {
         return "Roof{" +
             "color='" + color + '\'' +
+            "type='" + type + '\'' +
             '}';
     }
 
+    public RoofType getType() {
+        return type;
+    }
+
+    public Roof setType(RoofType type) {
+        this.type = type;
+        return this;
+    }
 }

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/RoofDto.java

@@ -20,6 +20,7 @@ package org.mapstruct.ap.test.nestedbeans;
 
 public class RoofDto {
     private String color;
+    private ExternalRoofType type;
 
     public RoofDto() {
     }
@@ -36,6 +37,15 @@ public class RoofDto {
         this.color = color;
     }
 
+    public ExternalRoofType getType() {
+        return type;
+    }
+
+    public RoofDto setType(ExternalRoofType type) {
+        this.type = type;
+        return this;
+    }
+
     @Override
     public boolean equals(Object o) {
         if ( this == o ) {
@@ -47,20 +57,26 @@ public class RoofDto {
 
         RoofDto roofDto = (RoofDto) o;
 
+        if ( type != ( (RoofDto) o ).type ) {
+            return false;
+        }
+
         return color != null ? color.equals( roofDto.color ) : roofDto.color == null;
 
     }
 
     @Override
     public int hashCode() {
-        return color != null ? color.hashCode() : 0;
+        int result = color != null ? color.hashCode() : 0;
+        result = 31 * result + ( type != null ? type.hashCode() : 0 );
+        return result;
     }
 
     @Override
     public String toString() {
         return "RoofDto{" +
             "color='" + color + '\'' +
+            "type='" + type + '\'' +
             '}';
     }
-
 }

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/RoofType.java

@@ -0,0 +1,28 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.nestedbeans;
+
+
+/**
+ * @author Filip Hrisafov
+ */
+public enum RoofType {
+
+    OPEN, BOX, GAMBREL
+}

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/TestData.java

@@ -33,7 +33,7 @@ public class TestData {
             new Wheel().rear().left(),
             new Wheel().rear().right()
         ) ),
-            new House( "Black", 1834, new Roof( 1 ) )
+            new House( "Black", 1834, new Roof( 1, RoofType.BOX ) )
         );
     }
 

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/UserDtoMapperClassic.java

@@ -40,4 +40,6 @@ public interface UserDtoMapperClassic {
 
     WheelDto mapWheel(Wheel wheels);
 
+    ExternalRoofType mapRoofType(RoofType roofType);
+
 }

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/ExternalRoofType.java

@@ -0,0 +1,28 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.nestedbeans.erroneous;
+
+
+/**
+ * @author Filip Hrisafov
+ */
+public enum ExternalRoofType {
+
+    OPEN, BOX, GAMBREL, STANDARD
+}

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/Roof.java

@@ -20,6 +20,7 @@ package org.mapstruct.ap.test.nestedbeans.erroneous;
 
 public class Roof {
     private Color color;
+    private RoofType type;
 
     public Color getColor() {
         return color;
@@ -28,4 +29,13 @@ public class Roof {
     public void setColor(Color color) {
         this.color = color;
     }
+
+    public RoofType getType() {
+        return type;
+    }
+
+    public Roof setType(RoofType type) {
+        this.type = type;
+        return this;
+    }
 }

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/RoofDto.java

@@ -20,6 +20,7 @@ package org.mapstruct.ap.test.nestedbeans.erroneous;
 
 public class RoofDto {
     private ColorDto color;
+    private ExternalRoofType type;
 
     public ColorDto getColor() {
         return color;
@@ -28,4 +29,12 @@ public class RoofDto {
     public void setColor(ColorDto color) {
         this.color = color;
     }
+
+    public ExternalRoofType getType() {
+        return type;
+    }
+
+    public void setType(ExternalRoofType type) {
+        this.type = type;
+    }
 }

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/RoofType.java

@@ -0,0 +1,28 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.nestedbeans.erroneous;
+
+
+/**
+ * @author Filip Hrisafov
+ */
+public enum RoofType {
+
+    OPEN, BOX, GAMBREL, NORMAL
+}

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/RoofTypeMapper.java

@@ -0,0 +1,32 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.nestedbeans.erroneous;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.ValueMapping;
+
+/**
+ * @author Filip Hrisafov
+ */
+@Mapper
+public interface RoofTypeMapper {
+
+    @ValueMapping( source = "NORMAL", target = "STANDARD")
+    ExternalRoofType map(RoofType type);
+}

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/UnmappableCollectionElementPropertyMapper.java

@@ -20,7 +20,7 @@ package org.mapstruct.ap.test.nestedbeans.erroneous;
 
 import org.mapstruct.Mapper;
 
-@Mapper
+@Mapper(uses = RoofTypeMapper.class)
 public abstract class UnmappableCollectionElementPropertyMapper {
 
     abstract UserDto userToUserDto(User user);

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/UnmappableDeepListMapper.java

@@ -20,7 +20,7 @@ package org.mapstruct.ap.test.nestedbeans.erroneous;
 
 import org.mapstruct.Mapper;
 
-@Mapper
+@Mapper(uses = RoofTypeMapper.class)
 public abstract class UnmappableDeepListMapper {
 
     abstract UserDto userToUserDto(User user);

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/UnmappableDeepMapKeyMapper.java

@@ -20,7 +20,7 @@ package org.mapstruct.ap.test.nestedbeans.erroneous;
 
 import org.mapstruct.Mapper;
 
-@Mapper
+@Mapper(uses = RoofTypeMapper.class)
 public abstract class UnmappableDeepMapKeyMapper {
 
     abstract UserDto userToUserDto(User user);

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/UnmappableDeepMapValueMapper.java

@@ -20,7 +20,7 @@ package org.mapstruct.ap.test.nestedbeans.erroneous;
 
 import org.mapstruct.Mapper;
 
-@Mapper
+@Mapper(uses = RoofTypeMapper.class)
 public abstract class UnmappableDeepMapValueMapper {
 
     abstract UserDto userToUserDto(User user);

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/UnmappableDeepNestingMapper.java

@@ -20,7 +20,7 @@ package org.mapstruct.ap.test.nestedbeans.erroneous;
 
 import org.mapstruct.Mapper;
 
-@Mapper
+@Mapper(uses = RoofTypeMapper.class)
 public abstract class UnmappableDeepNestingMapper {
 
     abstract UserDto userToUserDto(User user);

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/UnmappableEnumMapper.java

@@ -0,0 +1,47 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.nestedbeans.erroneous;
+
+import org.mapstruct.Mapper;
+
+@Mapper
+public abstract class UnmappableEnumMapper {
+
+    abstract UserDto userToUserDto(User user);
+
+    public ColorDto map(Color color) {
+        return new ColorDto();
+    }
+
+    public CarDto map(Car carDto) {
+        return new CarDto();
+    }
+
+    public DictionaryDto map(Dictionary dictionary) {
+        return new DictionaryDto();
+    }
+
+    public ComputerDto map(Computer computer) {
+        return new ComputerDto();
+    }
+
+    public CatDto map(Cat cat) {
+        return new CatDto();
+    }
+}

processor/src/test/java/org/mapstruct/ap/test/nestedbeans/erroneous/UnmappableValuePropertyMapper.java

@@ -20,7 +20,7 @@ package org.mapstruct.ap.test.nestedbeans.erroneous;
 
 import org.mapstruct.Mapper;
 
-@Mapper
+@Mapper(uses = RoofTypeMapper.class)
 public abstract class UnmappableValuePropertyMapper {
 
     abstract UserDto userToUserDto(User user);

processor/src/test/resources/fixtures/org/mapstruct/ap/test/nestedbeans/UserDtoMapperClassicImpl.java

@@ -0,0 +1,143 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.nestedbeans;
+
+import java.util.ArrayList;
+import java.util.List;
+import javax.annotation.Generated;
+
+@Generated(
+    value = "org.mapstruct.ap.MappingProcessor",
+    date = "2017-03-01T22:15:21+0100",
+    comments = "version: , compiler: javac, environment: Java 1.8.0_112 (Oracle Corporation)"
+)
+public class UserDtoMapperClassicImpl implements UserDtoMapperClassic {
+
+    @Override
+    public UserDto userToUserDto(User user) {
+        if ( user == null ) {
+            return null;
+        }
+
+        UserDto userDto = new UserDto();
+
+        userDto.setName( user.getName() );
+        userDto.setCar( carToCarDto( user.getCar() ) );
+        userDto.setSecondCar( carToCarDto( user.getSecondCar() ) );
+        userDto.setHouse( houseToHouseDto( user.getHouse() ) );
+
+        return userDto;
+    }
+
+    @Override
+    public CarDto carToCarDto(Car car) {
+        if ( car == null ) {
+            return null;
+        }
+
+        CarDto carDto = new CarDto();
+
+        carDto.setName( car.getName() );
+        carDto.setYear( car.getYear() );
+        List<WheelDto> list = mapWheels( car.getWheels() );
+        if ( list != null ) {
+            carDto.setWheels( list );
+        }
+
+        return carDto;
+    }
+
+    @Override
+    public HouseDto houseToHouseDto(House house) {
+        if ( house == null ) {
+            return null;
+        }
+
+        HouseDto houseDto = new HouseDto();
+
+        houseDto.setName( house.getName() );
+        houseDto.setYear( house.getYear() );
+        houseDto.setRoof( roofToRoofDto( house.getRoof() ) );
+
+        return houseDto;
+    }
+
+    @Override
+    public RoofDto roofToRoofDto(Roof roof) {
+        if ( roof == null ) {
+            return null;
+        }
+
+        RoofDto roofDto = new RoofDto();
+
+        roofDto.setColor( String.valueOf( roof.getColor() ) );
+        roofDto.setType( mapRoofType( roof.getType() ) );
+
+        return roofDto;
+    }
+
+    @Override
+    public List<WheelDto> mapWheels(List<Wheel> wheels) {
+        if ( wheels == null ) {
+            return null;
+        }
+
+        List<WheelDto> list = new ArrayList<WheelDto>();
+        for ( Wheel wheel : wheels ) {
+            list.add( mapWheel( wheel ) );
+        }
+
+        return list;
+    }
+
+    @Override
+    public WheelDto mapWheel(Wheel wheels) {
+        if ( wheels == null ) {
+            return null;
+        }
+
+        WheelDto wheelDto = new WheelDto();
+
+        wheelDto.setFront( wheels.isFront() );
+        wheelDto.setRight( wheels.isRight() );
+
+        return wheelDto;
+    }
+
+    @Override
+    public ExternalRoofType mapRoofType(RoofType roofType) {
+        if ( roofType == null ) {
+            return null;
+        }
+
+        ExternalRoofType externalRoofType;
+
+        switch ( roofType ) {
+            case OPEN: externalRoofType = ExternalRoofType.OPEN;
+            break;
+            case BOX: externalRoofType = ExternalRoofType.BOX;
+            break;
+            case GAMBREL: externalRoofType = ExternalRoofType.GAMBREL;
+            break;
+            default: throw new IllegalArgumentException( "Unexpected enum constant: " + roofType );
+        }
+
+        return externalRoofType;
+    }
+}

processor/src/test/resources/fixtures/org/mapstruct/ap/test/nestedbeans/UserDtoMapperSmartImpl.java

@@ -0,0 +1,221 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.nestedbeans;
+
+import java.util.ArrayList;
+import java.util.List;
+import javax.annotation.Generated;
+
+@Generated(
+    value = "org.mapstruct.ap.MappingProcessor",
+    date = "2017-03-01T22:15:23+0100",
+    comments = "version: , compiler: javac, environment: Java 1.8.0_112 (Oracle Corporation)"
+)
+public class UserDtoMapperSmartImpl implements UserDtoMapperSmart {
+
+    @Override
+    public UserDto userToUserDto(User user) {
+        if ( user == null ) {
+            return null;
+        }
+
+        UserDto userDto = new UserDto();
+
+        userDto.setName( user.getName() );
+        userDto.setCar( carToCarDto( user.getCar() ) );
+        userDto.setSecondCar( carToCarDto( user.getSecondCar() ) );
+        userDto.setHouse( houseToHouseDto( user.getHouse() ) );
+
+        return userDto;
+    }
+
+    @Override
+    public org.mapstruct.ap.test.nestedbeans.other.UserDto userToUserDto2(User user) {
+        if ( user == null ) {
+            return null;
+        }
+
+        org.mapstruct.ap.test.nestedbeans.other.UserDto userDto = new org.mapstruct.ap.test.nestedbeans.other.UserDto();
+
+        userDto.setName( user.getName() );
+        userDto.setCar( carToCarDto1( user.getCar() ) );
+        userDto.setHouse( houseToHouseDto1( user.getHouse() ) );
+
+        return userDto;
+    }
+
+    protected WheelDto wheelToWheelDto(Wheel wheel) {
+        if ( wheel == null ) {
+            return null;
+        }
+
+        WheelDto wheelDto = new WheelDto();
+
+        wheelDto.setFront( wheel.isFront() );
+        wheelDto.setRight( wheel.isRight() );
+
+        return wheelDto;
+    }
+
+    protected List<WheelDto> wheelListToWheelDtoList(List<Wheel> list) {
+        if ( list == null ) {
+            return null;
+        }
+
+        List<WheelDto> list1 = new ArrayList<WheelDto>();
+        for ( Wheel wheel : list ) {
+            list1.add( wheelToWheelDto( wheel ) );
+        }
+
+        return list1;
+    }
+
+    protected CarDto carToCarDto(Car car) {
+        if ( car == null ) {
+            return null;
+        }
+
+        CarDto carDto = new CarDto();
+
+        carDto.setName( car.getName() );
+        carDto.setYear( car.getYear() );
+        List<WheelDto> list = wheelListToWheelDtoList( car.getWheels() );
+        if ( list != null ) {
+            carDto.setWheels( list );
+        }
+
+        return carDto;
+    }
+
+    protected ExternalRoofType roofTypeToExternalRoofType(RoofType roofType) {
+        if ( roofType == null ) {
+            return null;
+        }
+
+        ExternalRoofType externalRoofType;
+
+        switch ( roofType ) {
+            case OPEN: externalRoofType = ExternalRoofType.OPEN;
+            break;
+            case BOX: externalRoofType = ExternalRoofType.BOX;
+            break;
+            case GAMBREL: externalRoofType = ExternalRoofType.GAMBREL;
+            break;
+            default: throw new IllegalArgumentException( "Unexpected enum constant: " + roofType );
+        }
+
+        return externalRoofType;
+    }
+
+    protected RoofDto roofToRoofDto(Roof roof) {
+        if ( roof == null ) {
+            return null;
+        }
+
+        RoofDto roofDto = new RoofDto();
+
+        roofDto.setColor( String.valueOf( roof.getColor() ) );
+        roofDto.setType( roofTypeToExternalRoofType( roof.getType() ) );
+
+        return roofDto;
+    }
+
+    protected HouseDto houseToHouseDto(House house) {
+        if ( house == null ) {
+            return null;
+        }
+
+        HouseDto houseDto = new HouseDto();
+
+        houseDto.setName( house.getName() );
+        houseDto.setYear( house.getYear() );
+        houseDto.setRoof( roofToRoofDto( house.getRoof() ) );
+
+        return houseDto;
+    }
+
+    protected org.mapstruct.ap.test.nestedbeans.other.WheelDto wheelToWheelDto1(Wheel wheel) {
+        if ( wheel == null ) {
+            return null;
+        }
+
+        org.mapstruct.ap.test.nestedbeans.other.WheelDto wheelDto = new org.mapstruct.ap.test.nestedbeans.other.WheelDto();
+
+        wheelDto.setFront( wheel.isFront() );
+        wheelDto.setRight( wheel.isRight() );
+
+        return wheelDto;
+    }
+
+    protected List<org.mapstruct.ap.test.nestedbeans.other.WheelDto> wheelListToWheelDtoList1(List<Wheel> list) {
+        if ( list == null ) {
+            return null;
+        }
+
+        List<org.mapstruct.ap.test.nestedbeans.other.WheelDto> list1 = new ArrayList<org.mapstruct.ap.test.nestedbeans.other.WheelDto>();
+        for ( Wheel wheel : list ) {
+            list1.add( wheelToWheelDto1( wheel ) );
+        }
+
+        return list1;
+    }
+
+    protected org.mapstruct.ap.test.nestedbeans.other.CarDto carToCarDto1(Car car) {
+        if ( car == null ) {
+            return null;
+        }
+
+        org.mapstruct.ap.test.nestedbeans.other.CarDto carDto = new org.mapstruct.ap.test.nestedbeans.other.CarDto();
+
+        carDto.setName( car.getName() );
+        carDto.setYear( car.getYear() );
+        List<org.mapstruct.ap.test.nestedbeans.other.WheelDto> list = wheelListToWheelDtoList1( car.getWheels() );
+        if ( list != null ) {
+            carDto.setWheels( list );
+        }
+
+        return carDto;
+    }
+
+    protected org.mapstruct.ap.test.nestedbeans.other.RoofDto roofToRoofDto1(Roof roof) {
+        if ( roof == null ) {
+            return null;
+        }
+
+        org.mapstruct.ap.test.nestedbeans.other.RoofDto roofDto = new org.mapstruct.ap.test.nestedbeans.other.RoofDto();
+
+        roofDto.setColor( String.valueOf( roof.getColor() ) );
+
+        return roofDto;
+    }
+
+    protected org.mapstruct.ap.test.nestedbeans.other.HouseDto houseToHouseDto1(House house) {
+        if ( house == null ) {
+            return null;
+        }
+
+        org.mapstruct.ap.test.nestedbeans.other.HouseDto houseDto = new org.mapstruct.ap.test.nestedbeans.other.HouseDto();
+
+        houseDto.setName( house.getName() );
+        houseDto.setYear( house.getYear() );
+        houseDto.setRoof( roofToRoofDto1( house.getRoof() ) );
+
+        return houseDto;
+    }
+}

processor/src/test/resources/fixtures/org/mapstruct/ap/test/nestedbeans/UserDtoUpdateMapperSmartImpl.java

@@ -0,0 +1,170 @@
+/**
+ *  Copyright 2012-2017 Gunnar Morling (http://www.gunnarmorling.de/)
+ *  and/or other contributors as indicated by the @authors tag. See the
+ *  copyright.txt file in the distribution for a full listing of all
+ *  contributors.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.mapstruct.ap.test.nestedbeans;
+
+import java.util.ArrayList;
+import java.util.List;
+import javax.annotation.Generated;
+
+@Generated(
+    value = "org.mapstruct.ap.MappingProcessor",
+    date = "2017-03-01T22:15:22+0100",
+    comments = "version: , compiler: javac, environment: Java 1.8.0_112 (Oracle Corporation)"
+)
+public class UserDtoUpdateMapperSmartImpl implements UserDtoUpdateMapperSmart {
+
+    @Override
+    public void userToUserDto(UserDto userDto, User user) {
+        if ( user == null ) {
+            return;
+        }
+
+        if ( user.getName() != null ) {
+            userDto.setName( user.getName() );
+        }
+        if ( user.getCar() != null ) {
+            if ( userDto.getCar() == null ) {
+                userDto.setCar( new CarDto() );
+            }
+            carToCarDto( user.getCar(), userDto.getCar() );
+        }
+        else {
+            userDto.setCar( null );
+        }
+        if ( user.getSecondCar() != null ) {
+            if ( userDto.getSecondCar() == null ) {
+                userDto.setSecondCar( new CarDto() );
+            }
+            carToCarDto( user.getSecondCar(), userDto.getSecondCar() );
+        }
+        else {
+            userDto.setSecondCar( null );
+        }
+        if ( user.getHouse() != null ) {
+            if ( userDto.getHouse() == null ) {
+                userDto.setHouse( new HouseDto() );
+            }
+            houseToHouseDto( user.getHouse(), userDto.getHouse() );
+        }
+        else {
+            userDto.setHouse( null );
+        }
+    }
+
+    protected WheelDto wheelToWheelDto(Wheel wheel) {
+        if ( wheel == null ) {
+            return null;
+        }
+
+        WheelDto wheelDto = new WheelDto();
+
+        wheelDto.setFront( wheel.isFront() );
+        wheelDto.setRight( wheel.isRight() );
+
+        return wheelDto;
+    }
+
+    protected List<WheelDto> wheelListToWheelDtoList(List<Wheel> list) {
+        if ( list == null ) {
+            return null;
+        }
+
+        List<WheelDto> list1 = new ArrayList<WheelDto>();
+        for ( Wheel wheel : list ) {
+            list1.add( wheelToWheelDto( wheel ) );
+        }
+
+        return list1;
+    }
+
+    protected void carToCarDto(Car car, CarDto mappingTarget) {
+        if ( car == null ) {
+            return;
+        }
+
+        if ( car.getName() != null ) {
+            mappingTarget.setName( car.getName() );
+        }
+        mappingTarget.setYear( car.getYear() );
+        if ( mappingTarget.getWheels() != null ) {
+            List<WheelDto> list = wheelListToWheelDtoList( car.getWheels() );
+            if ( list != null ) {
+                mappingTarget.getWheels().clear();
+                mappingTarget.getWheels().addAll( list );
+            }
+        }
+        else {
+            List<WheelDto> list = wheelListToWheelDtoList( car.getWheels() );
+            if ( list != null ) {
+                mappingTarget.setWheels( list );
+            }
+        }
+    }
+
+    protected ExternalRoofType roofTypeToExternalRoofType(RoofType roofType) {
+        if ( roofType == null ) {
+            return null;
+        }
+
+        ExternalRoofType externalRoofType;
+
+        switch ( roofType ) {
+            case OPEN: externalRoofType = ExternalRoofType.OPEN;
+            break;
+            case BOX: externalRoofType = ExternalRoofType.BOX;
+            break;
+            case GAMBREL: externalRoofType = ExternalRoofType.GAMBREL;
+            break;
+            default: throw new IllegalArgumentException( "Unexpected enum constant: " + roofType );
+        }
+
+        return externalRoofType;
+    }
+
+    protected void roofToRoofDto(Roof roof, RoofDto mappingTarget) {
+        if ( roof == null ) {
+            return;
+        }
+
+        mappingTarget.setColor( String.valueOf( roof.getColor() ) );
+        if ( roof.getType() != null ) {
+            mappingTarget.setType( roofTypeToExternalRoofType( roof.getType() ) );
+        }
+    }
+
+    protected void houseToHouseDto(House house, HouseDto mappingTarget) {
+        if ( house == null ) {
+            return;
+        }
+
+        if ( house.getName() != null ) {
+            mappingTarget.setName( house.getName() );
+        }
+        mappingTarget.setYear( house.getYear() );
+        if ( house.getRoof() != null ) {
+            if ( mappingTarget.getRoof() == null ) {
+                mappingTarget.setRoof( new RoofDto() );
+            }
+            roofToRoofDto( house.getRoof(), mappingTarget.getRoof() );
+        }
+        else {
+            mappingTarget.setRoof( null );
+        }
+    }
+}