ModelMapper：将 ID 字段从 DTO 映射到实体上的 ID 字段时出错

Question

I am trying to Map from a ProductReviewDTO which has an int product ID to link to the Product found on the ProductReview entity. However using ModelMapper it can't seem to map correctly. Resulting in a failed to set value error message as well as an IllegalArgument Exception saying that the object is not an instance of declaring class when trying to set the value.

The first mapping of ProductReview to ProductReviewDTO works fine.

DTO:

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class ProductReviewDTO {

    private int id;
    private int productId;
}

Entity:

@Data
@Entity
@Builder
@NoArgsConstructor
@AllArgsConstructor
@Table(name = "product_reviews")
public class ProductReview {

    @Id
    @SequenceGenerator(name="product_reviews_generator", sequenceName = "product_reviews_id_seq", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "product_reviews_generator")
    @Column(name = "id", updatable = false, nullable = false)
    private int id;

    @ManyToOne(cascade=CascadeType.DETACH, fetch = FetchType.LAZY)
    @JoinColumn(name = "product_id", nullable=false)
    private Product product;
}

Mapping:

@NoArgsConstructor
public class ProductReviewMapping implements BaseMapping<ProductReview, ProductReviewDTO> {

    @Override
    public PropertyMap<ProductReview, ProductReviewDTO> MapFromSourceToTarget() {
        return new PropertyMap<ProductReview, ProductReviewDTO>() {
            protected void configure() {
                map().setProductId(source.getProduct().getId());
                map().setUserId(source.getUser().getId());
                map().setRatingId(source.getRating().getId());
            }
        };
    }

    @Override
    public PropertyMap<ProductReviewDTO, ProductReview> MapFromTargetToSource() {
        return new PropertyMap<ProductReviewDTO, ProductReview>() {
            protected void configure() {
                map().setProduct(new Product().builder().id(source.getProductId()).build());
            }
        };
    }
}

Caused by: org.modelmapper.MappingException: ModelMapper mapping errors:

1) Failed to set value '1' on com.pfex.ecom.library.common.entity.Product$ProductBuilder.id()

Answer 1

This is old, but there are no answers and the issue still occurs so I will offer my solution.

I encountered a very similar issue using ModelMapper. The problem in essence is that ModelMapper does not support any complexity beyond getter/setter invocation inside of the PropertyMap logic (see this link ). Even the tertiary operator is too much. This is bewildering to me, but it is true.

In the OP's case, the fact that 'MapFromTargetToSource' is using a builder is too complex.

I found 3 options to work around this. I have listed them below with JUnit examples of each.
_{(Note: I don't have the BaseMapping class available in my version of ModelMapper (2.4.4), so I have a simpler one-way implementation but it works similarly. In practice, I wrap my use of ModelMapper inside of Converter Objects so these options are all encapsulated behind the convert() interface method.)}

Option 1: You can do all the derivation beforehand and set a simple value inside the configure() method.

@Test
public void modelMapper_complexMapping_option_1_externalDerivation_so() {
    ProductReviewDTO source = ProductReviewDTO.builder().id(123).productId(456).build();

    ModelMapper mapper = new ModelMapper();
    TypeMap<ProductReviewDTO, ProductReview> typeMap = mapper.typeMap(ProductReviewDTO.class, ProductReview.class);

    Product derivedField = Product.builder().id(source.getProductId()).build();

    PropertyMap<ProductReviewDTO, ProductReview> targetToSource = new PropertyMap<>() {
        protected void configure() {
            map().setProduct(derivedField);
        }
    };

    typeMap.addMappings(targetToSource);
    ProductReview actual = mapper.map(source, ProductReview.class);

    assertThat(actual.getId(), is(source.getId()));
    assertThat(actual.getProduct().getId(), is(source.getProductId()));
}

Option 2: You can write an internal method in your source class to derive the value. This may or may not make sense depending on use case, organization standards, etc. IMHO it does not make sense for a DTO like the OP is using, but may in other cases.

@Test
public void modelMapper_complexMapping_option_2_internalDerivation_so() {
    ProductReviewDTO source = ProductReviewDTO.builder().id(123).productId(456).build();

    ModelMapper mapper = new ModelMapper();
    TypeMap<ProductReviewDTO, ProductReview> typeMap = mapper.typeMap(ProductReviewDTO.class, ProductReview.class);

    PropertyMap<ProductReviewDTO, ProductReview> targetToSource = new PropertyMap<>() {
        protected void configure() {
            map().setProduct(source.synthesizeProduct());
        }
    };

    typeMap.addMappings(targetToSource);
    ProductReview actual = mapper.map(source, ProductReview.class);

    assertThat(actual.getId(), is(source.getId()));
    assertThat(actual.getProduct().getId(), is(source.getProductId()));
}

public class ProductReviewDTO {

    private int id;
    private int productId;

    public Product synthesizeProduct() {
        return Product.builder().id(getProductId()).build();
    }

}

Option 3: You can use ModelMapper's "using converter" syntax. I find this clunky, but it works. Here is a reference .

@Test
public void modelMapper_complexMapping_option_3_usingConverter_so() {
    ProductReviewDTO source = ProductReviewDTO.builder().id(123).productId(456).build();

    ModelMapper mapper = new ModelMapper();
    TypeMap<ProductReviewDTO, ProductReview> typeMap = mapper.typeMap(ProductReviewDTO.class, ProductReview.class);

    PropertyMap<ProductReviewDTO, ProductReview> targetToSource = new PropertyMap<>() {
        protected void configure() {
            using(new Converter<ProductReviewDTO, Product>() {
                public Product convert(MappingContext<ProductReviewDTO, Product> context) {
                    ProductReviewDTO src = context.getSource();
                    return Product.builder().id(src.getProductId()).build();
                }
            }).map(source).setProduct(null);
        }
    };

    typeMap.addMappings(targetToSource);
    ProductReview actual = mapper.map(source, ProductReview.class);

    assertThat(actual.getId(), is(source.getId()));
    assertThat(actual.getProduct().getId(), is(source.getProductId()));
}