Base Entity Class in JPA

In JPA entities there are repeated fields and methods. Don’t repeat yourself and write a base class with @MappedSuperclass.

Base entity common fields:

id: Table id column, auto increment. In entity model with @Id annotation.

version: Version column for Optimistic Lock has default ’0′ in table and managed from your database and EntityManager. In entity model with @Version annotation.

Common methods:

hashCode() and equals() very important. If you don’t implement the methods you get problems later.

toString(): Optional method, default I use class name and id. You can override this method in your entities.

package com.cemikta.entitydemo.model;

import java.io.Serializable;

import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;
import javax.persistence.Version;

/**
 * Base entity
 *
 * @author Cem Ikta
 */
@MappedSuperclass
public abstract class BaseEntity implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "id", nullable = false, columnDefinition = "BIGINT UNSIGNED")
    protected Long id;

    @Column(name = "version")
    @Version
    private Long version;

    public Long getId() {
        return id;
    }

    public Long getVersion() {
        return version;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (this.getId() != null ? this.getId().hashCode() : 0);

        return hash;
    }

    @Override
    public boolean equals(Object object) {
	if (this == object)
            return true;
        if (object == null)
            return false;
        if (getClass() != object.getClass())
            return false;

        BaseEntity other = (BaseEntity) object;
        if (this.getId() != other.getId() && (this.getId() == null || !this.id.equals(other.id))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return this.getClass().getName() + " [ID=" + id + "]";
    }
}

Base entity audit fields:

It is sometimes important to know when and by whom the table data were saved. I save creation date, modification date and user informations in the table. I have String for user informations, I save only username without foreign key, then I have no relations with user table. With @PrePersist and @PreUpdate you don’t need to set the date manual every time. Set the user informations(createdBy and updatedBy) in your controllers/service but not in models! Business logic must always remain in the right place.

If you need more flexible auditing/versioning of your tables, history of changes, you can use Hibernate Envers.

package com.cemikta.entitydemo.model;

import java.util.Date;
import javax.persistence.Column;
import javax.persistence.MappedSuperclass;
import javax.persistence.PrePersist;
import javax.persistence.PreUpdate;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.validation.constraints.Size;

/**
 * Base entity audit
 *
 * @author Cem Ikta
 */
@MappedSuperclass
public abstract class BaseEntityAudit extends BaseEntity {

    @Column(name = "created_at")
    @Temporal(TemporalType.TIMESTAMP)
    private Date createdAt;

    @Size(max = 20)
    @Column(name = "created_by", length = 20)
    private String createdBy;

    @Column(name = "updated_at")
    @Temporal(TemporalType.TIMESTAMP)
    private Date updatedAt;

    @Size(max = 20)
    @Column(name = "updated_by", length = 20)
    private String updatedBy;

    public Date getCreatedAt() {
            return createdAt;
    }

    public void setCreatedAt(Date createdAt) {
            this.createdAt = createdAt;
    }

    public String getCreatedBy() {
            return createdBy;
    }

    public void setCreatedBy(String createdBy) {
            this.createdBy = createdBy;
    }

    public Date getUpdatedAt() {
            return updatedAt;
    }

    public void setUpdatedAt(Date updatedAt) {
            this.updatedAt = updatedAt;
    }

    public String getUpdatedBy() {
            return updatedBy;
    }

    public void setUpdatedBy(String updatedBy) {
            this.updatedBy = updatedBy;
    }

    /**
     * Sets createdAt before insert
     */
    @PrePersist
    public void setCreationDate() {
        this.createdAt = new Date();
    }

    /**
     * Sets updatedAt before update
     */
    @PreUpdate
    public void setChangeDate() {
        this.updatedAt = new Date();
    }

}

 

Sample usage of EntityBaseAudit:

If you use your table id columns with table name prefix e.g customer_id then use @AttributeOverride. Without table name prefix remove @AttributeOverride.

@Entity
@Table(name = "customers")
@AttributeOverride(name = "id", column = @Column(name = "customer_id",
        nullable = false, columnDefinition = "BIGINT UNSIGNED"))
public class Customer extends BaseEntityAudit {

    // fields without id column ...

    public Customer() {
    }

    // getter and setter ...

}

 

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