BAEL-9152: Set the Null Value for a Target Property in Mapstruct (#18869)

* wraps up mapping using expression

* final version

Author: pedrolopes9-7

mapstruct-3/src/main/java/com/baeldung/setnullproperty/dto/ArticleDTO.java

@@ -0,0 +1,37 @@
+package com.baeldung.setnullproperty.dto;
+
+import java.util.Objects;
+
+public class ArticleDTO extends ReviewableDTO {
+
+    private String title;
+
+    public ArticleDTO(String title) {
+        this.title = title;
+    }
+
+    public ArticleDTO() {
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        ArticleDTO that = (ArticleDTO) o;
+        return Objects.equals(title, that.title);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(title);
+    }
+}

mapstruct-3/src/main/java/com/baeldung/setnullproperty/dto/ReviewableDTO.java

@@ -0,0 +1,37 @@
+package com.baeldung.setnullproperty.dto;
+
+import java.util.Objects;
+
+public class ReviewableDTO {
+
+    private String title;
+
+    public ReviewableDTO() {
+    }
+
+    public ReviewableDTO(String title) {
+        this.title = title;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        ReviewableDTO that = (ReviewableDTO) o;
+        return Objects.equals(title, that.title);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(title);
+    }
+}

mapstruct-3/src/main/java/com/baeldung/setnullproperty/dto/WeeklyNewsDTO.java

@@ -0,0 +1,42 @@
+package com.baeldung.setnullproperty.dto;
+
+import java.util.Objects;
+
+public class WeeklyNewsDTO extends ReviewableDTO {
+
+    private String title;
+
+    public WeeklyNewsDTO() {
+    }
+
+    public WeeklyNewsDTO(String title1) {
+        this.title = title1;
+    }
+
+    @Override
+    public String getTitle() {
+        return title;
+    }
+
+    @Override
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        if (!super.equals(o)) {
+            return false;
+        }
+        WeeklyNewsDTO that = (WeeklyNewsDTO) o;
+        return Objects.equals(title, that.title);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(super.hashCode(), title);
+    }
+}

mapstruct-3/src/main/java/com/baeldung/setnullproperty/entity/Article.java

@@ -0,0 +1,38 @@
+package com.baeldung.setnullproperty.entity;
+
+import java.util.Objects;
+
+public class Article extends Reviewable {
+
+    private String title;
+
+    public Article(String id, String reviewedBy) {
+        this.id = id;
+        this.reviewedBy = reviewedBy;
+    }
+
+    public Article() {
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        Article article = (Article) o;
+        return Objects.equals(id, article.id) && Objects.equals(reviewedBy, article.reviewedBy);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(id, reviewedBy);
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+}

mapstruct-3/src/main/java/com/baeldung/setnullproperty/entity/Reviewable.java

@@ -0,0 +1,54 @@
+package com.baeldung.setnullproperty.entity;
+
+import java.util.Objects;
+
+public class Reviewable {
+    protected String id;
+    protected String reviewedBy;
+    protected String title;
+
+    public Reviewable(String reviewedBy) {
+        this.reviewedBy = reviewedBy;
+    }
+
+    public Reviewable() {
+    }
+
+    public String getReviewedBy() {
+        return reviewedBy;
+    }
+
+    public void setReviewedBy(String reviewedBy) {
+        this.reviewedBy = reviewedBy;
+    }
+
+    public String getId() {
+        return id;
+    }
+
+    public void setId(String id) {
+        this.id = id;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        Reviewable that = (Reviewable) o;
+        return Objects.equals(reviewedBy, that.reviewedBy);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(reviewedBy);
+    }
+}

mapstruct-3/src/main/java/com/baeldung/setnullproperty/entity/WeeklyNews.java

@@ -0,0 +1,27 @@
+package com.baeldung.setnullproperty.entity;
+
+import java.util.Objects;
+
+public class WeeklyNews extends Reviewable {
+
+    public WeeklyNews() {
+    }
+
+    public WeeklyNews(String reviewedBy) {
+        this.reviewedBy = reviewedBy;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        WeeklyNews that = (WeeklyNews) o;
+        return Objects.equals(reviewedBy, that.reviewedBy);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(reviewedBy);
+    }
+}

mapstruct-3/src/main/java/com/baeldung/setnullproperty/mapper/ArticleMapper.java

@@ -0,0 +1,52 @@
+package com.baeldung.setnullproperty.mapper;
+
+import org.mapstruct.AfterMapping;
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+import org.mapstruct.MappingTarget;
+import org.mapstruct.Named;
+
+import com.baeldung.setnullproperty.dto.ArticleDTO;
+import com.baeldung.setnullproperty.entity.Article;
+
+@Mapper(uses = ReviewableMapper.class)
+public interface ArticleMapper {
+
+    @Mapping(target = "title", source = "dto.title")
+    @Mapping(target = "id", source = "persisted.id")
+    @Mapping(target = "reviewedBy", expression = "java(null)")
+    Article toArticleUsingExpression(ArticleDTO dto, Article persisted);
+
+    @Mapping(target = "title", source = "dto.title")
+    @Mapping(target = "id", source = "persisted.id")
+    @Mapping(target = "reviewedBy", expression = "java(getDefaultReviewStatus())")
+    Article toArticleUsingExpressionMethod(ArticleDTO dto, Article persisted);
+
+    default String getDefaultReviewStatus() {
+        return null;
+    }
+
+    @Mapping(target = "title", source = "dto.title")
+    @Mapping(target = "id", source = "persisted.id")
+    @Mapping(target = "reviewedBy", ignore = true)
+    Article toArticleUsingIgnore(ArticleDTO dto, Article persisted);
+
+    @AfterMapping
+    default void setNullReviewedBy(@MappingTarget Article article) {
+        article.setReviewedBy(null);
+    }
+
+    @Mapping(target = "title", source = "dto.title")
+    @Mapping(target = "id", source = "persisted.id")
+    Article toArticleUsingAfterMapping(ArticleDTO dto, Article persisted);
+
+    @Mapping(target = "title", source = "dto.title")
+    @Mapping(target = "id", source = "persisted.id")
+    @Mapping(target = "reviewedBy", qualifiedByName = "toNull")
+    Article toArticleUsingQualifiedBy(ArticleDTO dto, Article persisted);
+
+    @Named("toNull")
+    default String mapToNull(String property) {
+        return null;
+    }
+}

mapstruct-3/src/main/java/com/baeldung/setnullproperty/mapper/ReviewableMapper.java

@@ -0,0 +1,22 @@
+package com.baeldung.setnullproperty.mapper;
+
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+import org.mapstruct.SubclassMapping;
+
+import com.baeldung.setnullproperty.dto.ArticleDTO;
+import com.baeldung.setnullproperty.dto.ReviewableDTO;
+import com.baeldung.setnullproperty.dto.WeeklyNewsDTO;
+import com.baeldung.setnullproperty.entity.Article;
+import com.baeldung.setnullproperty.entity.Reviewable;
+import com.baeldung.setnullproperty.entity.WeeklyNews;
+
+@Mapper
+public interface ReviewableMapper {
+
+    @SubclassMapping(source = ArticleDTO.class, target = Article.class)
+    @SubclassMapping(source = WeeklyNewsDTO.class, target = WeeklyNews.class)
+    @Mapping(target = "reviewedBy", expression = "java(null)")
+    Reviewable toReviewable(ReviewableDTO dto);
+
+}

mapstruct-3/src/test/java/com/baeldung/setnullproperty/mapper/ArticleMapperUnitTest.java

@@ -0,0 +1,78 @@
+package com.baeldung.setnullproperty.mapper;
+
+import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mapstruct.factory.Mappers;
+
+import com.baeldung.setnullproperty.dto.ArticleDTO;
+import com.baeldung.setnullproperty.dto.WeeklyNewsDTO;
+import com.baeldung.setnullproperty.entity.Article;
+import com.baeldung.setnullproperty.entity.Reviewable;
+import com.baeldung.setnullproperty.entity.WeeklyNews;
+
+class ArticleMapperUnitTest {
+
+    private ArticleMapper articleMapper;
+    private ReviewableMapper reviewableMapper;
+
+    @BeforeEach
+    void setUp() {
+        articleMapper = Mappers.getMapper(ArticleMapper.class);
+        reviewableMapper = Mappers.getMapper(ReviewableMapper.class);
+    }
+
+    @Test
+    void givenArticleDTO_whenToArticleUsingExpression_thenReturnsArticleWithNullStatus() {
+        Article oldArticle1 = new Article("ID-1", "John Doe");
+        Article oldArticle2 = new Article("ID-2", "John Doe");
+
+        Article result1 = articleMapper.toArticleUsingExpression(new ArticleDTO("Updated article 1 title"), oldArticle1);
+        Article result2 = articleMapper.toArticleUsingExpressionMethod(new ArticleDTO("Updated article 2 title"), oldArticle2);
+
+        assertThat(result1.getReviewedBy()).isNull();
+        assertThat(result2.getReviewedBy()).isNull();
+        assertThat(result1.getTitle()).isEqualTo("Updated article 1 title");
+        assertThat(result2.getTitle()).isEqualTo("Updated article 2 title");
+    }
+
+    @Test
+    void givenArticleDTO_whenToArticleUsingIgnore_thenReturnsArticleWithNullStatus() {
+        Article oldArticle1 = new Article("ID-1", "John Doe");
+
+        Article result1 = articleMapper.toArticleUsingIgnore(new ArticleDTO("Updated article 1 title"), oldArticle1);
+
+        assertThat(result1.getReviewedBy()).isNull();
+        assertThat(result1.getTitle()).isEqualTo("Updated article 1 title");
+    }
+
+    @Test
+    void givenArticleDTO_whenToArticleUsingAfterMapping_thenReturnsArticleWithNullStatus() {
+        Article oldArticle1 = new Article("ID-1", "John Doe");
+
+        Article result1 = articleMapper.toArticleUsingAfterMapping(new ArticleDTO("Updated article 1 title"), oldArticle1);
+
+        assertThat(result1.getReviewedBy()).isNull();
+        assertThat(result1.getTitle()).isEqualTo("Updated article 1 title");
+    }
+
+    @Test
+    void givenArticleDTO_whenToArticleUsingQualifiedBy_thenReturnsArticleWithNullStatus() {
+        Article result1 = articleMapper.toArticleUsingQualifiedBy(new ArticleDTO("Updated article 1 title"), new Article("ID-1", "John Doe"));
+
+        assertThat(result1.getReviewedBy()).isNull();
+        assertThat(result1.getTitle()).isEqualTo("Updated article 1 title");
+    }
+
+    @Test
+    void givenArticleDTO_whenToReviewableUsingMapper_thenReturnsArticleWithNullStatus() {
+        Reviewable result1 = reviewableMapper.toReviewable(new ArticleDTO("Updated article 1 title"));
+        Reviewable result2 = reviewableMapper.toReviewable(new WeeklyNewsDTO());
+
+        assertThat(result1).isInstanceOf(Article.class);
+        assertThat(result2).isInstanceOf(WeeklyNews.class);
+        assertThat(result1.getReviewedBy()).isNull();
+        assertThat(result2.getReviewedBy()).isNull();
+    }
+}