JUnit with H2 Database : Unique index or primary key violation when adding multilingual services for multiple data

Question

During the creation of the database by Hibernate, it is adding a unique key constraint for the foreign key id_student in oe_iv_student_lang table because we have to implement the Serializable interface which results in Hibernate not letting us add multiple rows with same parent foreign key in its corresponding child table.

I have attached the snippet for better understanding..

Student Class:

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

@Entity
@Table(name = "oe_iv_student")
public class OeIvStudent {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id_student")
    private Integer idStudent;
}

Student Lang Class:

import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

@Entity
@Table(name = "oe_iv_student_lang")
public class OeIvStudentLang implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id_student_lang")
    private Integer idStudentLang;

    @OneToOne
    @JoinColumn(name = "id_student")
    private OeIvStudent idStudent;

    @Column(name = "ln_code")
    private String lnCode;
}

Location Class:

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

@Entity
@Table(name = "oe_locations")
public class OeLocations {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id_location")
    private Integer idLocation;

    @OneToOne
    @JoinColumn(name = "id_student", referencedColumnName = "id_student")
    private OeIvStudentLang idStudent;

    @Column(name = "code")
    private String code;
}

The reason I use Serializable interface is that I am mapping an Object of OeIvStudentLang class in OeLocations but the column being referenced is of OeIvStudent class. Having an Object of OeIvStudentLang makes it easier for me to naivgate throught the tables, i.e.

OeLocations->OeIvStudentLang->OeIvStudent

If I do not use Serializable in the OeIvStudentLangclass, Hibernate throws a Exception saying that OeIvStudentLang is not Serializable when I work with OeLocations class.If I were to use an Object of OeIvStudent instead, I would not be able to navigate to the lang class from OeLocations.

Please have a look and suggest what to be done.

Thanks :)

Answer 1

This hasn't anything to do with implementing Serializable.

You've defined the relationship between OeIvStudentLang and OeIvStudent as @OneToOne. This means that every OeIvStudentLang has exactly one OeIvStudent. As you've even stated, this should be a One-To-Many relationship, thus you need to change your mapping from @OneToOne to @OneToMany and it should remove this unique constraint.

For reference:

A one-to-one association is similar to many-to-one association with a difference that the column will be set as unique.