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2018/08/11

[JPA] Entity Inheritance in JPA

Problem
I have three tables which has two identical column (i.e. LAST_MODIFIED_BY and LAST_MODIFIED_DATETIME).
How do define entities via entity inheritance in JPA?

 How-To
There are two steps to implement entity inheritance:
[Step 1] Extract the two columns into an abstract class with @MappedSuperclass 
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  package test.entity;
  
  import java.io.Serializable;
  import java.util.Date;
  
  import javax.persistence.Column;
  import javax.persistence.MappedSuperclass;
  
  import org.springframework.data.annotation.LastModifiedBy;
  import org.springframework.data.annotation.LastModifiedDate;
  
  import lombok.Data;
  
  @Data
  @MappedSuperclass
  public abstract class CommonEntity implements Serializable {
  
      private static final long serialVersionUID = 1L;
  
      @LastModifiedBy
      @Column(name = "LAST_MODIFIED_BY")
      private String lastModifiedBy;
  
      @LastModifiedDate
      @Column(name = "LAST_MODIFIED_DATETIME")
      private Date lastModifiedDatetime;
  
  }

[Step 2] Extend the abstract class from the three entities:
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  package test.entity;
  
  import java.io.Serializable;
  
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.EntityListeners;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.SequenceGenerator;
  import javax.persistence.Table;
  
  import org.springframework.data.jpa.domain.support.AuditingEntityListener;
  
  import lombok.Data;
  import lombok.EqualsAndHashCode;
  
  @Entity
  @Table(name = "PROJECT")
  @Data
  @EqualsAndHashCode(of = "id", callSuper = false)
  public class Project extends CommonEntity implements Serializable {
  
      private static final long serialVersionUID = 1L;
      
      @Id
      @SequenceGenerator(name = "PROJECT_ID_SEQ", sequenceName = "PROJECT_ID_SEQ", allocationSize = 1)
      @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "PROJECT_ID_SEQ")
      @Column(name = "ID")
      private Integer id;
      
      @Column(name = "IDENTIFIER")
      private String identifier;
      
      @Column(name = "NAME")
      private String name;
      
      @Column(name = "STATUS")
      private String status;
  } 




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  package test.entity;
  
  import java.io.Serializable;
  
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.EntityListeners;
  import javax.persistence.Id;
  import javax.persistence.Lob;
  import javax.persistence.Table;
  
  import org.springframework.data.jpa.domain.support.AuditingEntityListener;
  
  import lombok.Data;
  import lombok.EqualsAndHashCode;
  
  @Entity
  @Table(name = "MODEL")
  @Data
  @EqualsAndHashCode(of = "id", callSuper = false)
  public class Model extends CommonEntity implements Serializable {
  
      private static final long serialVersionUID = 1L;
      
      @Id
      @Column(name = "ID")
      private String id;
      
      @Column(name = "PROJECT_ID")
      private Integer projectId;
      
      @Lob
      @Column(name = "STATISTICS_JSON")
      private String statisticsJson;
      
  }




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  package com.cht.ai.bot.entity;
  
  import java.io.Serializable;
  
  import javax.persistence.Column;
  import javax.persistence.Entity;
  import javax.persistence.EntityListeners;
  import javax.persistence.GeneratedValue;
  import javax.persistence.GenerationType;
  import javax.persistence.Id;
  import javax.persistence.SequenceGenerator;
  import javax.persistence.Table;
  
  import org.springframework.data.jpa.domain.support.AuditingEntityListener;
  
  import lombok.Data;
  import lombok.EqualsAndHashCode;
  
  @Entity
  @Table(name = "SLOT")
  @Data
  @EqualsAndHashCode(of = "id", callSuper = false)
  public class Slot extends CommonEntity implements Serializable {
  
      private static final long serialVersionUID = 1L;
      
      @Id
      @SequenceGenerator(name = "SLOT_ID_SEQ", sequenceName = "SLOT_ID_SEQ", allocationSize = 1)
      @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SLOT_ID_SEQ")
      @Column(name = "ID")
      private Integer id;
      
      @Column(name = "NAME")
      private String name;
      
      @Column(name = "TYPE")
      private String type;
      
  }


Posted by Albert Kuo at 8:00 AM
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