ManyToMany：MappingException：无法确定以下类型：java.util.List

Question

I have some tables :

PROFIL : id_profil, ...

EXPERIENCE : id_experience, id_profil#, ...

COMPETENCE_LEVEL : id_competence_level, level, ...

One PROFIL can have lot of EXPERIENCE and lot of COMPETENCE_LEVEL .

One EXPERIENCE can have lot of COMPETENCE_LEVEL .

One COMPETENCE_LEVEL concerns lot of EXPERIENCE .

So, for me, between EXPERIENCE and COMPETENCE_LEVEL, this is a (np) ManyToMany relation.

I tried:

PROFIL.java:

@Entity
@Table(name="profil")
public class Profil {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="id_profil")
    private Long idProfil;

    public Profil() {
        super();
    }

    public Long getIdProfil() {
        return idProfil;
    }

    public void setIdProfil(Long idProfil) {
        this.idProfil = idProfil;
    }

    @Override
    public String toString() {
        //[...]
    }

}

EXPERIENCE.java:

@Entity
@Table(name="experience")
public class Experience {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="id_experience")
    private Long idExperience;

    @ManyToOne
    @JoinColumn(name="id_profil")
    private Profil idProfil;

    private List<CompetenceLevel> competenceLevels;

    public Experience() {
        super();
        idProfil = new Profil();
    }

    public Long getIdExperience() {
        return idExperience;
    }

    public void setIdExperience(Long idExperience) {
        this.idExperience = idExperience;
    }

    public Profil getIdProfil() {
        return idProfil;
    }

    public void setIdProfil(Profil idProfil) {
        this.idProfil = idProfil;
    }

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "experience_competence_level", joinColumns = @JoinColumn(name = "id_experience", referencedColumnName = "id_experience"), inverseJoinColumns = @JoinColumn(name = "id_competence_level", referencedColumnName = "id_competence_level"))
    public List<CompetenceLevel> getCompetenceLevels() {
        return competenceLevels;
    }

    public void setCompetenceLevels(List<CompetenceLevel> competenceLevels) {
        this.competenceLevels = competenceLevels;
    }

    @Override
    public String toString() {
        // [...]
    }

}

COMPETENCE_LEVEL.java:

@Entity
@Table(name="competence_level")
public class CompetenceLevel {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="id_competence_level")
    private Long idCompetenceLevel;

    @OneToOne
    @JoinColumn(name="id_level")
    private Level level;

    @OneToOne
    @JoinColumn(name="id_profil")
    private Profil profil;

    private List<Experience> experiences;

    public CompetenceLevel() {
        super();
    }

    public Long getIdCompetenceLevel() {
        return idCompetenceLevel;
    }

    public void setIdCompetenceLevel(Long idCompetenceLevel) {
        this.idCompetenceLevel = idCompetenceLevel;
    }

    public Level getLevel() {
        return level;
    }

    public void setLevel(Level level) {
        this.level = level;
    }

    public Profil getProfil() {
        return profil;
    }

    public void setProfil(Profil profil) {
        this.profil = profil;
    }

    @ManyToMany(mappedBy = "competenceLevels")
    public List<Experience> getExperiences() {
        return experiences;
    }

    public void setExperiences(List<Experience> experiences) {
        this.experiences = experiences;
    }

    @Override
    public String toString() {
        // [...]
    }

}

So, I have this error :

org.hibernate.MappingException: Could not determine type for: java.util.List, at table: competence_level, for columns: [org.hibernate.mapping.Column(experiences)]

I don't understand why. I follow this tuto : https://hellokoding.com/jpa-many-to-many-relationship-mapping-example-with-spring-boot-maven-and-mysql/

Do you have an idea ? Thanks.

Answer 1

The reason is simply: don't mix field and method annotations in the same persistent class.

Hibernate generates an unclear error here. It is very hard to figure out the reason of the error, if you don't face it before.

Answer 2

In your code, you are mixing field access and property access. See this answer .

I would prefer using only one of the possibilities. I use field annotations, like you did for idProfil .

In the book "Professional Java for Web Applications" by Nicholas S. Williams (very, very good) I found this:

You should never mix JPA property annotations and JPA field annotations in the same entity. Doing so results in unspecified behaviour and is very likely to cause errors.

And just for clearness, I wouldn't write this

@ManyToOne
@JoinColumn(name="id_profil")
private Profil idProfil;
// better:
// private Profil profil;