use of entityManager.createNativeQuery(query,foo.class)

Question

I would like to return a List of Integers from a

javax.persistence.EntityManager.createNativeQuery call

Why is the following incorrect?

Answer 1

Suppose your query is "select id,name from users where rollNo = 1001".

Here query will return a object with id and name column. Your Response class is like bellow:

public class UserObject{
        int id;
        String name;
        String rollNo;

        public UserObject(Object[] columns) {
            this.id = (columns[0] != null)?((BigDecimal)columns[0]).intValue():0;
            this.name = (String) columns[1];
        }

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getRollNo() {
            return rollNo;
        }

        public void setRollNo(String rollNo) {
            this.rollNo = rollNo;
        }
    }

here UserObject constructor will get a Object Array and set data with object.

public UserObject(Object[] columns) {
            this.id = (columns[0] != null)?((BigDecimal)columns[0]).intValue():0;
            this.name = (String) columns[1];
        }

Your query executing function is like bellow :

public UserObject getUserByRoll(EntityManager entityManager,String rollNo) {

        String queryStr = "select id,name from users where rollNo = ?1";
        try {
            Query query = entityManager.createNativeQuery(queryStr);
            query.setParameter(1, rollNo);

            return new UserObject((Object[]) query.getSingleResult());
        } catch (Exception e) {
            e.printStackTrace();
            throw e;
        }
    }

Here you have to import bellow packages:

import javax.persistence.Query;
import javax.persistence.EntityManager;

Now your main class, you have to call this function. First you have to get EntityManager and call this getUserByRoll(EntityManager entityManager,String rollNo) function. Calling procedure is given bellow:

@PersistenceContext
private EntityManager entityManager;

UserObject userObject = getUserByRoll(entityManager,"1001");

Now you have data in this userObject.

Here is Imports

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

Note:

query.getSingleResult() return a array. You have to maintain the column position and data type.

select id,name from users where rollNo = ?1 

query return a array and it's [0] --> id and [1] -> name.

For more info, visit this Answer

Thanks :)