JPA Query Selecting Only Specific Columns Without Using Criteria Query

JPA & Criteria API - Select only specific columns

One of the JPA ways for getting only particular columns is to ask for a Tuple object.

In your case you would need to write something like this:

CriteriaQuery<Tuple> cq = builder.createTupleQuery();
// write the Root, Path elements as usual
Root<EntityClazz> root = cq.from(EntityClazz.class);
cq.multiselect(root.get(EntityClazz_.ID), root.get(EntityClazz_.VERSION));  //using metamodel
List<Tuple> tupleResult = em.createQuery(cq).getResultList();
for (Tuple t : tupleResult) {
    Long id = (Long) t.get(0);
    Long version = (Long) t.get(1);
}

Another approach is possible if you have a class representing the result, like T in your case. T doesn't need to be an Entity class. If T has a constructor like:

public T(Long id, Long version)

then you can use T directly in your CriteriaQuery constructor:

CriteriaQuery<T> cq = builder.createQuery(T.class);
// write the Root, Path elements as usual
Root<EntityClazz> root = cq.from(EntityClazz.class);
cq.multiselect(root.get(EntityClazz_.ID), root.get(EntityClazz_.VERSION));  //using metamodel
List<T> result = em.createQuery(cq).getResultList();

See this link for further reference.

JPA Query selecting only specific columns without using Criteria Query?

Yes, like in plain sql you could specify what kind of properties you want to select:

SELECT i.firstProperty, i.secondProperty FROM ObjectName i WHERE i.id=10

Executing this query will return a list of Object[], where each array contains the selected properties of one object.

Another way is to wrap the selected properties in a custom object and execute it in a TypedQuery:

String query = "SELECT NEW CustomObject(i.firstProperty, i.secondProperty) FROM ObjectName i WHERE i.id=10";
TypedQuery<CustomObject> typedQuery = em.createQuery(query , CustomObject.class);
List<CustomObject> results = typedQuery.getResultList();

Examples can be found in this article.

UPDATE 29.03.2018:

@Krish:

@PatrickLeitermann for me its giving "Caused by: org.hibernate.hql.internal.ast.QuerySyntaxException: Unable to locate class ***" exception . how to solve this ?

I guess you’re using JPA in the context of a Spring application, don't you? Some other people had exactly the same problem and their solution was adding the fully qualified name (e. g. com.example.CustomObject) after the SELECT NEW keywords.

Maybe the internal implementation of the Spring data framework only recognizes classes annotated with @Entity or registered in a specific orm file by their simple name, which causes using this workaround.

Spring JPA selecting specific columns

You can set nativeQuery = true in the @Query annotation from a Repository class like this:

public static final String FIND_PROJECTS = "SELECT projectId, projectName FROM projects";

@Query(value = FIND_PROJECTS, nativeQuery = true)
public List<Object[]> findProjects();

Note that you will have to do the mapping yourself though. It's probably easier to just use the regular mapped lookup like this unless you really only need those two values:

public List<Project> findAll()

It's probably worth looking at the Spring data docs as well.

Spring boot JPA & Criteria API - Select single column

in CustomRepositoryMethod replace first
line CriteriaQuery<Comment> cq = cb.createQuery(Comment.class); to CriteriaQuery<Note> cq = cb.createQuery(Note.class)

cb.createQuery parameter accept result Class in docs you can see.

update

// assuming query like
// select oComment from comment inner join Note on comment.noteuuid=Note.noteuuid where Note.noteUuid = 1 and version > 0;

CriteriaBuilder cb = em.getCriteriaBuilder();
// data type of oComment
CriteriaQuery<Note> query = cb.createQuery(Note.class);
// from comment
Root<Comment> comment = query.from(Comment.class);

//join
Join<Comment, Note> note = comment.join(comment.get("oNote"));

//version Condition
Predicate version=cb.greaterThan(comment.get("version"),0 );

//Note condition
predicate note=cb.equal(note.get("noteuuid"),note.getNoteUuid());

// get oComment and where condtion 
query.select(comment.get("oComment")).where(cb.and(version,note));

    return  em.createQuery(query).setFirstResult(iOffset).setMaxResults(iResultSize).getResultList();

Selecting specific columns in jpa 2 Criteria API?

Yes, it does. The select() method is what you need to use. From the openJPA manual:

The select() method defines the result of the query. If left unspecified, the select projection is assumed to be the root domain object. However, you can specify the selected projections explicitly as a list: qdef.select(customer.get(Customer_.name), order.get(Order_.status));

I want to select specific columns specified by user in Spring boot JPA and Angular 7

For dynamic filters you can use Query By Example in simple cases or Specifications in more advanced cases.

Limiting the columns selected is normally done in Spring Data JPA by using a projection interface as return value.
But doing that dynamically is not possible and either way you can't combine it with the options for dynamic where clauses.

Therefore the solution is to implement a custom method, get an EntityManager injected, construct your query as required using the Criteria API or String concatenation of a JPQL statement (not recommended due to the risk of SQL injection).

Hibernate Criteria Query to get specific columns

Use Projections to specify which columns you would like to return.

Example

SQL Query

SELECT user.id, user.name FROM user;

Hibernate Alternative

Criteria cr = session.createCriteria(User.class)
    .setProjection(Projections.projectionList()
      .add(Projections.property("id"), "id")
      .add(Projections.property("Name"), "Name"))
    .setResultTransformer(Transformers.aliasToBean(User.class));

  List<User> list = cr.list();

Distinct on specific column using JPA Specification

You can't use Specifications because you want to return a List of Strings.

So you could use JPQL

@Query("select distinct h.name from Hcp h where area = 'Dhaka'")
List<String> findDistinctName();