Spring JPA抽象类行为

Question

I have question, what am I doing wrong, my entities are displayed not like I would like, when I go to the h2-console I can see 3 tables, persons employee manager when I go to the persons table I see all persons that extend this abstract class ( employee , manager ), but when I go to the other tables I can only see id of this classes. My question is how to fix it, and also how to make each table to display the id staring from 1 because now the employee table has 3 ids 1,2,3 and the manager table has 4,5 , the person table is displayed correctly. I would like to display 3 employees in the employee table, 2 managers in the managers table, and each entity in the persons table, and the ids staring counting from 1 in every table.

Abstract class Person

@Entity
@Inheritance(strategy = InheritanceType.JOINED)
@DiscriminatorColumn(name = "descriminatorColumn")
@Table(name = "persons")
public abstract class Person {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;

@Column(name = "first_name")
private String firstName;

@Column(name = "last_name")
private String lastName;

@Column(name = "email")
private String address;

@Column(name = "age")
private int age;

public Person(String firstName, String lastName, String address, int age) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.address = address;
    this.age = age;
}

public String getFirstName() {
    return firstName;
}

public void setFirstName(String firstName) {
    this.firstName = firstName;
}

public String getLastName() {
    return lastName;
}

public void setLastName(String lastName) {
    this.lastName = lastName;
}

public String getAddress() {
    return address;
}

public void setAddress(String address) {
    this.address = address;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}

@Override
public String toString() {
    return "Person{" +
            "firstName='" + firstName + '\'' +
            ", lastName='" + lastName + '\'' +
            ", address='" + address + '\'' +
            ", age=" + age +
            '}';
  }
}

Manager class extends Person abstract class

@Entity
@Table(name = "managers")
public class Manager extends Person {

public Manager(String firstName, String lastName, String email, int age) {
    super(firstName, lastName, email, age);
}

@Override
public String toString() {
    return super.toString();
 }
}

Employee class extends Person abstract class

@Entity
@Table(name = "employees")
public class Employee extends Person {

public Employee(String firstName, String lastName, String address, int age) {
    super(firstName, lastName, address, age);
}

@Override
public String toString() {
    return super.toString();
  }
}

Answer 1

My question is how to fix it

There is absolutely nothing to fix as by using JOINED inheritance type it is doing exactly what you have specified, viz:

• save the data common to employeee and manager in persons table.
• save the the data specific to employees in the employees table.
• save the data specific to managers in the managers table.

https://en.wikibooks.org/wiki/Java_Persistence/Inheritance#Joined,_Multiple_Table_Inheritance

Currently Employee and Manager define no additional fields and so only the IDs exist in these tables.

If that is not to change then you would probably be better off using SINGLE_TABLE inheritance with a discriminator column so all the data will be in 1 table.

https://en.wikibooks.org/wiki/Java_Persistence/Inheritance#Example_single_table_inheritance_table_in_database

The final option is not to have any inheritance at all at the database level ie have 2 tables employees and managers which define all fields for each type. You can do that using @MappedSuperclass which prevents the need to duplicate the JPA mappings in the Java class hierarchy.

https://en.wikibooks.org/wiki/Java_Persistence/Inheritance#Mapped_Superclasses

but be aware with this approach you cannot query for all persons but only for managers and employees separately.