How to map a list of Objects into a table with hibernate in spring?

Question

I am trying to map a list of Users to a location object but I get a Mapping Exception. This is because the List object is not recognized by database ? Or why do I get this exception ?

This is my user class :

@Entity
@Table(name = "users")
public class NewUser extends BaseEntity{
    private String login;
    private String fullName;

    private Location location;
    private Department department;
    private Role role;
    private Long days;
    private String team;
    private Long managerId;
    private String hiredDate;

    public String getLogin() {
        return login;
    }

    public void setLogin(String login) {
        this.login = login;
    }

    public String getFullName() {
        return fullName;
    }

    public void setFullName(String fullName) {
        this.fullName = fullName;
    }

    public Location getLocation() {
        return location;
    }

    @ManyToOne(targetEntity = Location.class)
    @JoinTable(name = "location")
    public void setLocation(Location location) {
        this.location = location;
    }

    public Department getDepartment() {
        return department;
    }

    @ManyToOne(targetEntity = Department.class)
    public void setDepartment(Department department) {
        this.department = department;
    }

    public Role getRole() {
        return role;
    }

    @ManyToOne(targetEntity = Role.class)
    @JoinTable(name = "role")
    public void setRole(Role role) {
        this.role = role;
    }

And location class:

@Entity
@Table(name = "location")
public class Location extends BaseEntity{
    private List<NewUser> users;

    public List<NewUser> getUsers() {
        return users;
    }

    @OneToMany(targetEntity = NewUser.class, mappedBy = "location")
    @JoinTable(name = "users")
    public void setUsers(List<NewUser> users) {
        this.users = users;
    }
}

Base entity:

@MappedSuperclass
public abstract class BaseEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }
}

The error is :

Caused by: org.hibernate.MappingException: Could not determine type for: java.util.List, at table: location, for columns: [org.hibernate.mapping.Column(users)]

How to effectively make relational mapping using hibernate annotations ?

Answer 1

Your mappings are incorrect. Assuming you want a FK in users table pointing to corresponding location then use the following:

In User

@ManyToOne
@JoinColumn(name = "location_id")
public void setLocation(Location location) {
    this.location = location;
}

In Location

@OneToMany(mappedBy = "location")
public void setUsers(List<NewUser> users) {
    this.users = users;
}

If you did not want the foreign key to Location in the users table then you could use a join table 'user_locations' with columns user_id (FK to users) and location_id (FK to locations) and use the @JoinTable annotation to specify it accordingly. In your mappings this would look like:

@ManyToOne
@JoinTable(name = "user_locations", joinColumns = @JoinColumn(name="user_id"), inverseJoinColumns = @JoinColumn(name = "location_id"))
public void setLocation(Location location) {
    this.location = location;
}

Answer 2

Hibernate already knows the table for each of the entities, as you're specifiying it using the @Table annotation. You're stablishing two independent relations instead of a two-side one.

Using mappedBy , declare the other entitiy's field you want to rely on:

Location.java

@OneToMany(fetch=FetchType.LAZY, cascade = {CascadeType.ALL}, mappedBy="location")
public List<NewUser> getUsers() {
    return users;
}

NewUser.java

@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name="id_user")
public Location getLocation() {
    return location;
}

See also:

• Can someone please explain mappedBy in hibernate?
• JPA JoinColumn vs mappedBy