Inheritance Mapping

Basically there are 3 types of inheritance mapping. We may use those methods suitably.

• SINGLE_TABLE (default)
• JOINED
• TABLE_PER_CLASS

Model

• Single Table inheritance (default strategy) 

Classes

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


@Entity
public class Project {

 private int projectID;
 private String projectName;

 @Id
 @GeneratedValue
 public int getProjectID() {
  return projectID;
 }

 public void setProjectID(int projectID) {
  this.projectID = projectID;
 }

 public String getProjectName() {
  return projectName;
 }

 public void setProjectName(String projectName) {
  this.projectName = projectName;
 }

}

Classes

import javax.persistence.Entity;


@Entity
public class Module extends Project {

 private String moduleName;

 public String getModuleName() {
  return moduleName;
 }

 public void setModuleName(String moduleName) {
  this.moduleName = moduleName;
 }

}

Classes

import javax.persistence.Entity;


@Entity
public class Task extends Module {

 private String taskName;

 public String getTaskName() {
  return taskName;
 }

 public void setTaskName(String taskName) {
  this.taskName = taskName;
 }

}

Result

• Joined inheritance

in this strategy we need to use special annotation called @Inheritance

@Inheritance(strategy=InheritanceType.JOINED)

We have to put this annotation for the top class in the inheritance hierarchy.

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class Project {

 private int projectID;
 private String projectName;

 @Id
 @GeneratedValue
 public int getProjectID() {
  return projectID;
 }
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Result :

•  TABLE_PER_CLASS Strategy