How to map oneToMany using ModelMapper

Question

I am using springBoot, I want to map OneToMany relationship from parent to child. Directly using entity with eager fetching I get recursive records, therefore, trying using ModelMapper for DTO mapping to Entity but I am not able to figure out how to do it. Please assume getters and setters.

Parent.java

@Entity
public class Parent {

    @Id
    private int parentId;

    private String a;

    @OneToMany(mappedBy = "parent")
    private Set<Child> child;

Child.java

@Entity
public class Child {

    @Id
    private int childId;

    private String c;

    @ManyToOne
    @JoinColumn(name = "b")
    private Parent parent;

I have working repository and servicelayer with findAll method.

ParentDto.java

public class ParentDto {

    private String a;

    private Set<Child> child;

ParentController.java

@RestController
public class ParentController {

    @Autowired
    private ModelMapper modelMapper;

    @Autowired
    private ParentService parentService;


    @RequestMapping(method = RequestMethod.GET, value="/parents" )
    public List<ParentDto> getParents() {
        List<Parent> parents =  parentService.getAll();
        return parents.stream()
                .map(x-> modelMapper.map(x, ParentDto.class))
                .collect(Collectors.toList());
    }
}

Error: While trying to fetch http://localhost:8080/parents

.
.
ModelMapper mapping errors: 1) Converter org.modelmapper.internal.converter.CollectionConverter@51381583 failed to convert java.util.Set to java.util.Set. 1 error
org.modelmapper.MappingException: ModelMapper mapping errors:

1) Converter org.modelmapper.internal.converter.CollectionConverter@51381583 failed to convert java.util.Set to java.util.Set.

1 error
    at org.modelmapper.internal.Errors.throwMappingExceptionIfErrorsExist(Errors.java:380)
    at org.modelmapper.internal.MappingEngineImpl.map(MappingEngineImpl.java:80)
.
.

1) Directly passing domain/entity to frontend is not recommended. 2) By recursive I mean infinite loop of parent->child->parent->child..... and JVM crashes. That's obviously a problem. I might get around that problem by using eager at parent and lazy at child though haven't tried, for the same I switched to DTO — garg10may
– garg10may, Commented Jun 13, 2019 at 7:20
And that is why EAGER is not the recommended fetch type... You can also always write your own custom mapper for domain model to DTO — XtremeBaumer
– XtremeBaumer, Commented Jun 13, 2019 at 7:21
And without the configuration of your ModelMapper we cant help you — XtremeBaumer
– XtremeBaumer, Commented Jun 13, 2019 at 7:23
Possible duplicate of Infinite Recursion with Jackson JSON and Hibernate JPA issue — Alan Hay
– Alan Hay, Commented Jun 13, 2019 at 7:25

helleye · Accepted Answer · 2020-02-28 00:55:26Z

0

This has nothing to do with “N + 1” and “Infinite Recursion” issue ，May be add Conver method to mapper； Mapping Children with ModelMapper https://amydegregorio.com/2018/10/03/mapping-children-with-modelmapper/

answered Feb 28, 2020 at 0:55

helleye

464 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

helleye Over a year ago

This blog use MapStruct to mapping one to many relation；“Automating Code with MapStruct：medium.com/@swathisprasad/…”

Yunnosch · Accepted Answer · 2022-11-17 06:47:58Z

0

I propose "Preferred nested properties".
http://modelmapper.org/user-manual/configuration

edited Nov 17, 2022 at 6:47

Yunnosch

26.8k9 gold badges46 silver badges66 bronze badges

answered Nov 17, 2022 at 6:34

vi0

3701 gold badge2 silver badges13 bronze badges

3 Comments

vi0 Over a year ago

@AttilaT My answer contains more than just a link

Attila T Over a year ago

Prefixing a link with a sentence that contains only five words, three out of which are direct quote from the page linked is essentially a link-only answer.

vi0 Over a year ago

@AttilaT I indicated a specific place to use the link. That is why I quoted him exactly.

4b0 · Accepted Answer · 2020-02-28 06:58:02Z

-1

You need to use @JsonIgnore annotation on the parent mapping defined in your child entity.

Refer this documentation for more info - https://fasterxml.github.io/jackson-annotations/javadoc/2.5/com/fasterxml/jackson/annotation/JsonIgnore.html

edited Feb 28, 2020 at 6:58

4b0

22.4k30 gold badges97 silver badges143 bronze badges

answered Feb 28, 2020 at 6:56

TeJas

683 silver badges7 bronze badges

Collectives™ on Stack Overflow

How to map oneToMany using ModelMapper

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related