How to construct an Entity class using Spring Data JpaRepository when using @Query

Question

Here's my use case

My JPA Repo interface

@Repository
public interface MyJpaRepository extends JpaRepository<MyEntity, Integer> {

//Example query that illustrates working with multiple tables only. Ignore the details of join conditions
    @Query(value="SELECT a.p, a.q,a.r , b.s, b.t, c.u,c.v FROM a, b, c
WHERE a.p=?1,b.s=?2,c.u=5"+ 
            "ORDER BY b.t",nativeQuery = true)
    List<MyEntity> findByPAndS(String p, Integer s);

}

In this scenario, how should my Entity look like? Here's my draft

@Entity
public class MyEntity {

    @Column
    private Integer p;

    @Column
    private Integer q;

    @Column
    private String r;

    @Column
    private String s;

    @Column
    private String t;

    @Column
    private String u;

    @Column
    private Double v;

    public MyEntity(){
    }
}

Are there any issues with my Entity declaration? How does JPA/Spring Data infer which table a specific column is associated with? If I need to define that explicitly, how can I do that?

Entities are mapped to tables. If you want to map individual values from various tables to a Java object then see stackoverflow.com/questions/16420697/… or create a DB view comprising the necessary data and map an entity to that. — Alan Hay
– Alan Hay, Commented Dec 14, 2016 at 20:28

Community · Accepted Answer · 2017-05-23 10:30:42Z

As said by Alan Hay, one @Entity class ist usually mapped to one table in your database. Without a "name" parameter the table name is infered by the class name (class MyFoo -> Table "MyFoo"). If you wish to refer another table you can explicitly set it like so:

@Entity(name = "MyTableName")
class MyFoo {}

Concerning your class members: if the member name matches the columns name you don't necessarily need the @Column Annotation.

@Entity
class MyFoo {
    private String bar;
}

Will map to Table "MyFoo" with column "bar", until you explicitely use another name:

@Column(name = "Mycolumn")
private String bar;

As you have 3 Tables one usually would create 3 @Entity classes and 3 Repositories to access them and the domain objects reference each other (see @OneToOne, @OneToMany, and so on,..)

If you definitely want to stick with a single Entity for multiple tables you might check this SO answer, using @SecondaryTable: is-possible-map-a-single-entity-with-multiple-tables-using-jpa

0gam · Accepted Answer · 2016-12-15 04:38:03Z

@Entity
@Table
public class Employee {

   @Id
   @GeneratedValue(strategy = GenerationType.AUTO)  

   private int eid;
   private String ename;
   private double salary;
   private String deg;

   public Employee(int eid, String ename, double salary, String deg) {
      super( );
      this.eid = eid;
      this.ename = ename;
      this.salary = salary;
      this.deg = deg;
   }

   public Employee( ) {
      super();
   }

   public int getEid( ) {
      return eid;
   }

   public void setEid(int eid) {
      this.eid = eid;
   }

   public String getEname( ) {
      return ename;
   }

   public void setEname(String ename) {
      this.ename = ename;
   }

   public double getSalary( ) {
      return salary;
   }

   public void setSalary(double salary) {
      this.salary = salary;
   }

   public String getDeg( ) {
      return deg;
   }

   public void setDeg(String deg) {
      this.deg = deg;
   }
}

I think you need this link.enter link description here

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