Using List or Set in JPA 2.1 for multiple columns in same table

Question

I am new with JPA. I am building sample maven project with Wicket-Spring-Hibernate-JPA.

I am using Hibernate EntityManager: v4.3.5.Final. I am using JPA: v2.1-api. I am using database mySql: v5.6.

When I am writing a model class, I want to map tables multiple columns with an element in model class as List or Set.

Database Table Name:  QUESTION_MAIN
Column Name : Type : PK
QID         : int : PK
QTYPE       : varchar
QUESTION    : varchar
OPTION1     : varchar
OPTION2     : varchar
OPTION3     : varchar
OPTION4     : varchar
OPTION5     : varchar
OPTION6     : varchar

Note: Assuming that there will be maximum 6 options to question.

Now in model class, I want to represent this like:

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="QUESTION_MAIN")
public class Question {

   @Id
   @GeneratedValue
   @Column(name="QID")
   private Long id;

   @Column(name="QTYPE")
   private String quest_type;

   @Column(name="QUESTION")
   private String question;

   //TODO: Create List or Set for OPTIONS
}

For the line in code:

//TODO: Create List or Set for OPTIONS

I want to create a List or Set for the options columns here.

Please do let me know any possible way for this. Or if anyone aware of such situation, provide any alternative to this.

---

Hello Luiggi, I am not sure the above link you provided solves my issue. Still I am trying to understand the option provided in that link. What I am looking for is, can I be able to create a List or Set of ColumnNames as one element in our Bean Class (with JPA Annotations).

Answer 1

At least, need to map entity property to table column. So simply need property (variable, getter&setter) for each OPTIONS in entity;

...
@Column(name="OPTION") //here OPTION1, OPTION2, and so on
private String option;
...

Another way is to create a separate table and an entity for OPTION to fulfill your requirement. From Question entity can do relationship to Option entity (one-to-many uni or bidirectional relationship - below example used bidirectional)

@Entity
@Table(name="OPTION")
public class Option {
    @Id
    @GeneratedValue
    @Column(name="") //column name in table
    private Long id;

    @Column(name="")
    private String optionTitle; //can use enum for OPTION1, OPTION2, and so on

    @Column(name="")
    private String optionValue;

    @ManyToOne
    @JoinColumn(name = "QUESTION_ID", nullable = false)   //QUESTION_ID (whatever you defined foreign key column in Option table)
    private Question question;

    ..
    //constructor, getters & setters
}

In Question entity, add property for option collection (List, Set and any sortable collection as you needed)

@OneToMany(mappedBy = "question")
private List<Option> optionList = new ArrayList<Option>();