Mistalis Mistalis - 1 month ago 15
Java Question

Hibernate's ManyToMany simple use

I've two entities :

CollabEntity
and
TechnoEntity
.


  • A collab can use several technos.

  • A techno can be used by several collabs.



I would like to know all technos used by a specific collab.

My DB looks like :

CREATE TABLE collabs(
co_id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
co_firstname VARCHAR(25) NOT NULL,
co_lastname VARCHAR(30) NOT NULL,
);

CREATE TABLE technos(
te_id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
te_tech VARCHAR(20)
);

CREATE TABLE cote( //Joins Collab & Techno
co_id INT NOT NULL,
te_id INT NOT NULL,
CONSTRAINT fk_cote_co_id FOREIGN KEY(co_id) REFERENCES collabs(co_id),
CONSTRAINT fk_cote_te_id FOREIGN KEY(te_id) REFERENCES technos(te_id),
PRIMARY KEY(co_id, te_id)
);





CollabEntity.java

@Entity
@Table(name = "collabs")
public class CollabEntity {
@Id
@GeneratedValue
@Column(name = "co_id")
private long id;

@Column(name = "co_firstname", nullable = false)
private String firstname;

@Column(name = "co_lastname", nullable = false)
private String lastname;

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "technos",
joinColumns = {@JoinColumn(name = "co_id", nullable = false, updatable = false)},
inverseJoinColumns = @JoinColumn(name = "te_id")
)
private Set<TechnoEntity> technos = new HashSet<TechnoEntity>();

protected CollabEntity() {
}

public CollabEntity(String firstname, String lastname) {
this.firstname = firstname;
this.lastname = lastname;
}

public long getId() {
return id;
}

public String getFirstname() {
return firstname;
}

public String getLastname() {
return lastname;
}

public Set<TechnoEntity> getTechnos() {
return technos;
}
}





TechnoEntity.java

@Entity
@Table(name = "technos")
public class TechnoEntity {
@Id
@GeneratedValue
@Column(name = "te_id")
private long id;

@Column(name = "te_tech")
private String tech;

@ManyToMany(mappedBy="technos")
private Set<CollabEntity> collabs = new HashSet<CollabEntity>();

protected TechnoEntity() {}

public TechnoEntity(String techno) {
this.tech = techno;
}

public long getId() {
return id;
}

public String getTech() {
return tech;
}
}


It's been a few hours I try things without finding a solution. This is my error :


Exception in thread "main"
org.springframework.beans.factory.BeanCreationException: Error
creating bean with name 'entityManagerFactory' defined in class path
resource [fr/xxx/dao/DatabaseConfig.class]: Invocation of init method
failed; nested exception is javax.persistence.PersistenceException:
[PersistenceUnit: default] Unable to build Hibernate SessionFactory


Precisely :


Caused by: org.hibernate.MappingException: Foreign key
(FK_pc2r8qfxqv9jpgsfxrs61kfql:technos [te_id])) must have same number
of columns as the referenced primary key (technos [co_id,te_id])


Thanks for your help :)

Answer

Change many to many mapping in CollabEntity. You need to change join table name. i.e. name from technos to some other name.

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "collab_technos", 
               joinColumns = {@JoinColumn(name = "co_id", nullable = false, updatable = false)},
               inverseJoinColumns = @JoinColumn(name = "te_id")
    )