one to many relation JPA example

DrRakha

The one to many relation between comment and topic table table is represented in the following code .One to many and one to many is bidirectional . I used @OneToMany and @ManyToOne .

Code:

FetchType.LAZY

Means don't load the object until the get function is accessed .This saves memory and avoid unneeded hits.

Code:

cascade=CascadeType.ALL

Means one the referenced record deleted ( here topic) , all the other records use this reference is deleted .(here is comments)

Here the code example between the table "comment" and "topic" .

Topic entity :

Code:

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import java.util.Date;
import java.util.Set;

import javax.persistence.SequenceGenerator;

@Entity
@Table(name="TOPIC")
@SequenceGenerator(sequenceName="TOPIC_SEQ",name="TOPIC_SEQ_GEN")
public class topic {

    private long Id;
    private String title;
    private Date creationDate;
    private Date modifedDate;
    private String content;
    private String pending;
    private String editUser;
    private Set<comment> commentSet;
    
    @Id
    @GeneratedValue(generator="TOPIC_SEQ_GEN",strategy=GenerationType.SEQUENCE)
    public long getId() {
        return Id;
    }
    public void setId(long id) {
        Id = id;
    }
    
    @Column(name="TITLE")
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    
    @Column(name="CREATION_DATE")
    public Date getCreationDate() {
        return creationDate;
    }
    public void setCreationDate(Date creationDate) {
        this.creationDate = creationDate;
    }
    
    @Column(name="MODIFED_DATE")
    public Date getModifedDate() {
        return modifedDate;
    }
    public void setModifedDate(Date modifedDate) {
        this.modifedDate = modifedDate;
    }
    
    @Column(name="CONTENT")
    public String getContent() {
        return content;
    }
    public void setContent(String content) {
        this.content = content;
    }
    
    public void setPending(String pending) {
        this.pending = pending;
    }
    @Column(name="PENDING")
    public String getPending() {
        return pending;
    }
    public void setEditUser(String editUser) {
        this.editUser = editUser;
    }
    @Column(name="EDIT_USER")
    public String getEditUser() {
        return editUser;
    }
    public void setCommentSet(Set<comment> commentSet) {
        this.commentSet = commentSet;
    }
    @OneToMany(fetch=FetchType.LAZY,cascade=CascadeType.ALL,mappedBy="topic")
    public Set<comment> getCommentSet() {
        return commentSet;
    }
}
 

comment entity :

Code:

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;

@Entity
@Table(name="COMMENT")
@SequenceGenerator(sequenceName="COMMENT_SEQ",name="COMMENT_SEQ_GEN")
public class comment {
    private long id;
    private String content;
    private topic topic;
    
    public void setId(long id) {
        this.id = id;
    }
    @Id
    @GeneratedValue(generator="COMMENT_SEQ_GEN",strategy=GenerationType.SEQUENCE)
    public long getId() {
        return id;
    }
    
    @Column(name="CONTENT")
    public void setContent(String content) {
        this.content = content;
    }
    public String getContent() {
        return content;
    }
    
   
    public void setTopic(topic topic) {
        this.topic = topic;
    }
 @ManyToOne(fetch =  FetchType.LAZY)
    @JoinColumn(name = "TOPIC_ID", nullable = false)
    public topic getTopic() {
        return topic;
    }
    

}
 

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one to many relation JPA example

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