Hibernate join two entities - spring

Question

i really don't know what actually my problem is.
I have two models in my Project.
model-package
Ansprechpartner
Lieferant
Ansprechpartner.java
#Entity
#Table(name = "ANSPRECHPARTNER")
#EntityListeners(AuditingEntityListener.class)
#JsonIgnoreProperties(value = {"anlageAm", "updatedAt"}, allowGetters = true)
public class Ansprechpartner {
...
#NotNull
#ManyToOne
#JoinColumn(name = "lief_code", foreignKey=#ForeignKey(name = "APART_LIEF_FK"))
private Lieferanten liefCode;
public Lieferanten getLiefCode() {
return liefCode;
}
public void setLiefCode(Lieferanten liefCode) {
this.liefCode = liefCode;
}
...
}
Lieferant.java
#Entity
#Table(name = "LIEFERANTEN")
#EntityListeners(AuditingEntityListener.class)
#JsonIgnoreProperties(value = {"anlageAm"}, allowGetters = true)
public class Lieferanten {
...
#Id
private String code;
#OneToMany(mappedBy = "liefCode")
private Set<Ansprechpartner> apart;
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
public Set<Ansprechpartner> getApart() {
return apart;
}
public void setApart(Set<Ansprechpartner> apart) {
this.apart = apart;
}
...
}
My Controller:
#RestController
#RequestMapping("/apart")
public class AnsprechpartnerController {
...
#GetMapping("/all/{id}")
public Ansprechpartner getApartWithId(#PathVariable("id") long id) {
Ansprechpartner apart = apartRepository.findOne(id);
return apartRepository.findOne(id);
}
}
When i try to get the json data i get the following problem. Ansprechpartner gets data from Lieferant (because of that join). But then Lieferant again shows data from Ansprechpartner and so on.
Maybe better described with the following picture:
Image with explanation
EDIT:
I finally solved it with the #JsonIgnoreProperties annotation:
In my Ansprechpartner.java i did it this way:
#NotNull
#JsonIgnoreProperties("apart")
// #JsonManagedReference
#ManyToOne
#JoinColumn(
name = "lief_code",
foreignKey=#ForeignKey(name = "APART_LIEF_FK")
)
private Lieferanten liefCode;
And in my Lieferanten.java i did it this way:
// #JsonBackReference
#JsonIgnoreProperties("liefCode")
#OneToMany(mappedBy = "liefCode", fetch = FetchType.LAZY)
private Set<Ansprechpartner> apart;

Answer 1

To avoid infinite recursions you can use #JsonManagedReference & #JsonBackReference
Json Infinite Recursion is one of the most common problems when we serialize Java objects which having Bidirectional-Relationships.
#JsonManagedReference: a part with the annotation will be serialized normally.
#JsonBackReference: a part with the annotation will be omitted from serialization.
like:
#JsonBackReference
private Set<Ansprechpartner> apart;
You can check details in solution-2

Answer 2

Strange behaviour. Possibly you could try:
1) Make sure in the Lieferanten entity, in the equals / hashCode you do not use the Set<Ansprechpartner> apart.
2) You can explicitly detach the entities from the persistence context:
#NotNull
#ManyToOne
#JoinColumn(name = "lief_code"
, foreignKey=#ForeignKey(name = "APART_LIEF_FK")
, cascade={CascadeType.DETACH})
private Lieferanten liefCode;
and then in the controller:
#GetMapping("/all/{id}")
public Ansprechpartner getApartWithId(#PathVariable("id") long id) {
Ansprechpartner apart = apartRepository.findOne(id);
apartRepository.detach(apart);
return apart;
}
you would need to implement a bit -> link, in repository in order to have that available.
3) explicitly add lazy loading: #OneToMany(mappedBy = "liefCode", fetch = FetchType.LAZY).

Answer 3

The root cause is jackson trying to serialize object when object has Bidirectional-Relationships.
You can fixed it by this way
Short way
Better way :
Returning entities directly to view layer is not a good practice.
You should convert entities to DTOs (Data Transfer Object) and pass the DTOs to view