JPA : How to convert a native query result set to

Question

I am using JPA in my project.

I came to a query in which I need to make join operation on five tables. So I created a native query which returns five fields.

Now I want to convert the result object to java POJO class which contains the same five Strings.

Is there any way in JPA to directly cast that result to POJO object list ??

I came to the following solution ..

@NamedNativeQueries({  
    @NamedNativeQuery(  
        name = "nativeSQL",  
        query = "SELECT * FROM Actors",  
        resultClass = db.Actor.class),  
    @NamedNativeQuery(  
        name = "nativeSQL2",  
        query = "SELECT COUNT(*) FROM Actors",  
        resultClass = XXXXX) // <--------------- problem  
})  

Now here in resultClass, do we need to provide a class which is actual JPA entity ? OR We can convert it to any JAVA POJO class which contains the same column names ?

Answer 1

Yes, with JPA 2.1 it's easy. You have very useful Annotations. They simplify your life.

First declare your native query, then your result set mapping (which defines the mapping of the data returned by the database to your POJOs). Write your POJO class to refer to (not included here for brevity). Last but not least: create a method in a DAO (for example) to call the query. This worked for me in a dropwizard (1.0.0) app.

First declare a native query in an entity class:

@NamedNativeQuery (
name = "domain.io.MyClass.myQuery",
query = "Select a.colA, a.colB from Table a",
resultSetMapping = "mappinMyNativeQuery")   // must be the same name as in the SqlResultSetMapping declaration

Underneath you can add the resultset mapping declaration:

@SqlResultSetMapping(
name = "mapppinNativeQuery",  // same as resultSetMapping above in NativeQuery
   classes = {
      @ConstructorResult( 
          targetClass = domain.io.MyMapping.class
          columns = {
               @ColumnResult( name = "colA", type = Long.class),  
               @ColumnResult( name = "colB", type = String.class)
          }
      )
   } 
)

Later in a DAO you can refer to the query as

public List<domain.io.MyMapping> findAll() {
        return (namedQuery("domain.io.MyClass.myQuery").list());
    }

That's it.

Answer 2

First declare following annotations:

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface NativeQueryResultEntity {
}

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface NativeQueryResultColumn {
    int index();
}

Then annotate your POJO as follows:

@NativeQueryResultEntity
public class ClassX {
    @NativeQueryResultColumn(index=0)
    private String a;

    @NativeQueryResultColumn(index=1)
    private String b;
}

Then write annotation processor:

public class NativeQueryResultsMapper {

    private static Logger log = LoggerFactory.getLogger(NativeQueryResultsMapper.class);

    public static <T> List<T> map(List<Object[]> objectArrayList, Class<T> genericType) {
        List<T> ret = new ArrayList<T>();
        List<Field> mappingFields = getNativeQueryResultColumnAnnotatedFields(genericType);
        try {
            for (Object[] objectArr : objectArrayList) {
                T t = genericType.newInstance();
                for (int i = 0; i < objectArr.length; i++) {
                    BeanUtils.setProperty(t, mappingFields.get(i).getName(), objectArr[i]);
                }
                ret.add(t);
            }
        } catch (InstantiationException ie) {
            log.debug("Cannot instantiate: ", ie);
            ret.clear();
        } catch (IllegalAccessException iae) {
            log.debug("Illegal access: ", iae);
            ret.clear();
        } catch (InvocationTargetException ite) {
            log.debug("Cannot invoke method: ", ite);
            ret.clear();
        }
        return ret;
    }

    // Get ordered list of fields
    private static <T> List<Field> getNativeQueryResultColumnAnnotatedFields(Class<T> genericType) {
        Field[] fields = genericType.getDeclaredFields();
        List<Field> orderedFields = Arrays.asList(new Field[fields.length]);
        for (int i = 0; i < fields.length; i++) {
            if (fields[i].isAnnotationPresent(NativeQueryResultColumn.class)) {
                NativeQueryResultColumn nqrc = fields[i].getAnnotation(NativeQueryResultColumn.class);
                orderedFields.set(nqrc.index(), fields[i]);
            }
        }
        return orderedFields;
    }
}

Use above framework as follows:

String sql = "select a,b from x order by a";
Query q = entityManager.createNativeQuery(sql);

List<ClassX> results = NativeQueryResultsMapper.map(q.getResultList(), ClassX.class);

Answer 3

If you use Spring-jpa, this is a supplement to the answers and this question. Please correct this if any flaws. I have mainly used three methods to achieve "mapping result Object[] to a pojo" based on what practical need I meet:

1. JPA built in method is enough.
2. JPA built in method is not enough, but a customized sql with its Entity are enough.

3. The former 2 failed, and I have to use a nativeQuery. Here are the examples. The pojo expected:

   public class Antistealingdto {
   
       private String secretKey;
   
       private Integer successRate;
   
       // GETTERs AND SETTERs
   
       public Antistealingdto(String secretKey, Integer successRate) {
           this.secretKey = secretKey;
           this.successRate = successRate;
       }
   }
   

Method 1: Change the pojo into an interface:

public interface Antistealingdto {
    String getSecretKey();
    Integer getSuccessRate();
}

And repository:

interface AntiStealingRepository extends CrudRepository<Antistealing, Long> {
    Antistealingdto findById(Long id);
}

Method 2: Repository:

@Query("select new AntistealingDTO(secretKey, successRate) from Antistealing where ....")
Antistealing whatevernamehere(conditions);

Note: parameter sequence of POJO constructor must be identical in both POJO definition and sql.

Method 3: Use @SqlResultSetMapping and @NamedNativeQuery in Entity as the example in Edwin Dalorzo's answer.

The first two methods would call many in-the-middle handlers, like customized converters. For example, AntiStealing defines a secretKey, before it is persisted, a converter is inserted to encrypt it. This would result in the first 2 methods returning a converted back secretKey which is not what I want. While the method 3 would overcome the converter, and returned secretKey would be the same as it is stored (an encrypted one).

Answer 4

See example below for using a POJO as pseudo entity to retrieve result from native query without using complex SqlResultSetMapping. Just need two annotations, a bare @Enity and a dummy @Id in your POJO. @Id can be used on any field of your choice, an @Id field can have duplicate keys but not null values.

Since @Enity does not map to any physical table, so this POJO is called a pseudo entity.

Environment: eclipselink 2.5.0-RC1, jpa-2.1.0, mysql-connector-java-5.1.14

You can download complete maven project here

Native query is based on mysql sample employees db http://dev.mysql.com/doc/employee/en/employees-installation.html

persistence.xml

<?xml version="1.0" encoding="UTF-8"?><persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.1" 
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
<persistence-unit name="jpa-mysql" transaction-type="RESOURCE_LOCAL">
    <class>org.moonwave.jpa.model.pojo.Employee</class>
    <properties>
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/employees" />
        <property name="javax.persistence.jdbc.user" value="user" />
        <property name="javax.persistence.jdbc.password" value="***" />
        <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
    </properties>
</persistence-unit>

Employee.java

package org.moonwave.jpa.model.pojo;

@Entity
public class Employee {

@Id
protected Long empNo;

protected String firstName;
protected String lastName;
protected String title;

public Long getEmpNo() {
    return empNo;
}
public void setEmpNo(Long empNo) {
    this.empNo = empNo;
}
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 getTitle() {
    return title;
}
public void setTitle(String title) {
    this.title = title;
}
public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("empNo: ").append(empNo);
    sb.append(", firstName: ").append(firstName);
    sb.append(", lastName: ").append(lastName);
    sb.append(", title: ").append(title);
    return sb.toString();
}
}

EmployeeNativeQuery.java

public class EmployeeNativeQuery {
private EntityManager em;
private EntityManagerFactory emf;

public void setUp() throws Exception {
    emf=Persistence.createEntityManagerFactory("jpa-mysql");
    em=emf.createEntityManager();
}
public void tearDown()throws Exception {
    em.close();
    emf.close();
}

@SuppressWarnings("unchecked")
public void query() {
    Query query = em.createNativeQuery("select e.emp_no as empNo, e.first_name as firstName, e.last_name as lastName," + 
            "t.title from employees e join titles t on e.emp_no = t.emp_no", Employee.class);
    query.setMaxResults(30);
    List<Employee> list = (List<Employee>) query.getResultList();
    int i = 0;
    for (Object emp : list) {
        System.out.println(++i + ": " + emp.toString());
    }
}

public static void main( String[] args ) {
    EmployeeNativeQuery test = new EmployeeNativeQuery();
    try {
        test.setUp();
        test.query();
        test.tearDown();
    } catch (Exception e) {
        System.out.println(e);
    }
}
}

Answer 5

Since others have already mentioned all the possible solutions, I am sharing my workaround solution.

In my situation with Postgres 9.4, while working with Jackson,

//Convert it to named native query.
List<String> list = em.createNativeQuery("select cast(array_to_json(array_agg(row_to_json(a))) as text) from myschema.actors a")
                   .getResultList();

List<ActorProxy> map = new ObjectMapper().readValue(list.get(0), new TypeReference<List<ActorProxy>>() {});

I am sure you can find same for other databases.

Also FYI, JPA 2.0 native query results as map

Answer 6

Simple way to converting SQL query to POJO class collection ,

Query query = getCurrentSession().createSQLQuery(sqlQuery).addEntity(Actors.class);
List<Actors> list = (List<Actors>) query.list();
return list;