Hibernate SQL Query result Mapping/Convert TO Object/Class/Bean

Question

1 2: select (table.*)/(all column) is OK

String sql = "select t_student.* from t_student";
//String sql = "select t_student.id,t_student.name,... from t_student"; //select all column
SQLQuery query = session.createSQLQuery(sql);
query.addEntity(Student.class);//or query.addEntity("alias", Student.class);
//query.list();[Student@..., Student@..., Student@...]
query.setResultTransformer(Transformers.ALIAS_TO_ENTITY_MAP); //or other transformer
query.list(); //[{Student(or alias)=Student@...},{Student=Student@...}]

3: select some column(not all of), is Error

String sql = "select t_student.id,t_student.name.t_student.sex from t_student";
SQLQuery query = session.createSQLQuery(sql);
query.addEntity(Student.class);
query.setResultTransformer(Transformers.ALIAS_TO_ENTITY_MAP);
query.list(); //Exception:invalid column/no column

I want "3" to work ok, and let the result can be mapped to Student.class.
Like: Student[id=?, name=?, sex=?, (other field are null/default)]
I've no idea for this error, help me please!

Answer 1

You can go further and add .setResultTransformer(Transformers.aliasToBean(YOUR_DTO.class)); and automatically map it to your custom dto object, see also Returning non-managed entities.

For example:

public List<MessageExtDto> getMessagesForProfile2(Long userProfileId) {
    Query query = getSession().createSQLQuery("  "
            + " select a.*, b.* "
            + " from messageVO AS a "
            + " INNER JOIN ( SELECT max(id) AS id, count(*) AS count FROM messageVO GROUP BY messageConversation_id) as b ON a.id = b.id "
            + " where a.id > 0 "
            + " ")
            .addScalar("id", new LongType())
            .addScalar("message", new StringType())
            ......... your mappings
            .setResultTransformer(Transformers.aliasToBean(MessageExtDto.class));

    List<MessageExtDto> list = query.list();
    return list;
}

Answer 2

I want "3" to work ok, and let the result can be mapped to Student.class

That's possible using
Query createNativeQuery(String sqlString, String resultSetMapping)

In the second argument you could tell the name of the result mapping. For example:

1) Let's consider a Student entity, the magic is going to be in the SqlResultSetMapping annotation:

import javax.persistence.Entity;
import javax.persistence.SqlResultSetMapping;
import javax.persistence.Table;

@Entity
@Table(name = "student")
@SqlResultSetMapping(name = "STUDENT_MAPPING", classes = {@ConstructorResult(
    targetClass = Student.class, columns = {
      @ColumnResult(name = "name"),
      @ColumnResult(name = "address")
})})
public class Student implements Serializable {
   private String name;
   private String address;

   /* Constructor for the result mapping; the key is the order of the args*/ 
   public Student(String aName, String anAddress) {
       this.name = aName;
       this.address = anAddress;
   }

   // the rest of the entity
}

2) Now you can execute a query which results will be mapped by STUDENT_MAPPING logic:

String query = "SELECT s FROM student s";
String mapping = "STUDENT_MAPPING";
Query query = myEntityManager.createNativeQuery(query, mapping);
@SuppressWarnings("unchecked")
List<Student> students = query.getResultList();
for (Student s : students) {
   s.getName(); // ...
}

Note: I think it's not possible to avoid the unchecked warning.