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How can I map a result set to custom POJO in JPA

I need to fetch 6 columns by joining 3 different tables. I have declared them as NamedNativequery on top of the entity class and I have used create named query method form JPA. When I try fo fetch the result set i get the list of array objects instead of the List of objects of POJO type. is there any external mapping should I be defining in order to map the result set to an external POJO?

You certainly can. This should help:
#NamedNativeQuery(query = "SELECT t1.col1, t2.col2 FROM t1 JOIN t2 ON ...", name = "MyNamedQuery", resultSetMapping = "MyPojoMapper")
#SqlResultSetMapping(name = "MyPojoMapper", classes = #ConstructorResult(
targetClass = MyPojo.class,
columns = {
#ColumnResult(name = "col1", type = String.class),
#ColumnResult(name = "cols", type = String.class)
}))
Then use it as such:
NativeQuery query = session.getNamedNativeQuery("MyNamedQuery");
MyPojo result = (MyPojo) query.getSingleResult();

You can use projection to specify what properties you want to get
https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#projections
or directly get with JPQL:
Repository.java
#Repository
public class CustomRepositoryImpl {
#Autowired
private EntityManager entityManager;
public List<Dto> find() {
var query = "SELECT new Dto(
x.Field1,
y.Field2,
z.Field3,
...)
FROM XxxEntity x
LEFT JOIN YyyEntity y
LEFT JOIN ZzzEntity z"
var jpqlQuery = entityManager.createQuery(query);
return jpqlQuery.getResultList();
}
}
Dto.java
public class Dto {
// Must have parameterized constructor with all fields what used in Repository
public Dto(int field1, String field2, String field3, ...) {
}
}

How to show values from table without using Entities?

I am trying to do "sql interpreter" in my web-app, only for CRUD. Everything work fine, I am using method prepareStatement() to execute query. But I have problem with operation select :
When I use the select operation only for 1 field, then parsing to a string gives a fairly good result:
for(String x: resultList){
System.out.println(x);
}
Is there any way to execute:
SELECT field_1, field_2, field_3 FROM table;
and print result in console, with some neat form without use Entites?
Well if it isn't possible, is there any way to generate entity "on the fly"? I mean generate Entities using java code.

You could use a native query and explicitly specify which columns you want to select:
String sql = "SELECT field_1, field_2, field_3 FROM table";
Query q = em.createNativeQuery(sql);
List<Object[]> results = q.getResultList();
for (Object[] r : results) {
System.out.println("(field_1, field_2, field_3) = (" + r[0] + ", " + r[1] + ", " + r[2] + ")");
}

With Spring Data JPA Projections
If you already use some entities and Spring Repository then you can add this code to one of them. Thanks Spring Data JPA Projections.
public interface SomeEntityRepository extends Repository<SomeEntity, Long> {
#Query(value = "SELECT field_1, field_2, field_3 FROM table", nativeQuery = true)
List<TableDto> getFromTable();
}
Where TableDto:
public interface TableDto{
Long getField_1();
String getField_2();
String getField_3();
}
With Spring JdbcTemplate
Or use Spring JdbcTemplate:
String query = "SELECT field_1, field_2, field_3 FROM table where id = ?";
List<TableDto> resluts = jdbcTemplate.queryForObject(
query, new Object[] { id }, new TableDtoRowMapper());
public class TableDtoRowMapper implements RowMapper<TableDto> {
#Override
public TableDtomapRow(ResultSet rs, int rowNum) throws SQLException {
TableDto dto = new TableDto();
dto.setField_1(rs.getString("field_1"));
dto.setField_2(rs.getString("field_2"));
dto.setField_3(rs.getString("field_3"));
return dto;
}
}
In this example TableDto is real class with getters and setters.

Can we call or combine Select and a procedure in Spring data jpa #Query

I have a procedure written in database. my_procedure(val1, val2)
So, lets say I have a database query like this:
select field1 as fieldName, field2 as fieldId
(select * from mydb.my_procedure(id)) as aValue // A procedure call
from mydb.my_table
I want to convert this to Spring's Data JPA #Query. Something like this:
#Query (" HERE I WANT THE ABOVE QUERY TO IMPLEMENT")
public List<MyTable> getDetails ()
Are we allowed to do this?
UPDATE
For example I have below query which I want to convert.
select id, name, roll,
(select * from db.calculate_fee (date, id)) fee
from Student
where id = 1 AND roll = 5
I want to do something like
#Query("SELECT student, (select * from db.calculate_fee (date, id) fee FROM Student student "
+ "WHERE student.id=:id, "
+ "AND student.name=:roll")
public List<Student> getDetails(#Param("id") Integer id, #Param("roll") Integer roll);
Is there anyway to do this?

Have you tried it with a native query?
#Query(nativeQuery = true, value = "select field1 as fieldName, field2 as fieldId...")
List<MyTable> getDetails();
(by the way, public is not needed for 'getDetails' as Repositories are interfaces)

#NamedStoredProcedureQueries({
#NamedStoredProcedureQuery(name = "getAllEmployees",
procedureName = "get_all_employees",
resultClasses = Employees.class)
})
#Procedure(name = "getAllEmployees")
List<Employees> getAllEmployees();
Complete tutorial

mapping Hibernate query results to custom class?

Following up on a question I posted yesterday: How to populate POJO class from custom Hibernate query?
Can someone show me an example of how to code the following SQL in Hibernate, and get the results correctly?
SQL:
select firstName, lastName
from Employee
What I'd like to do, if it's possible in Hibernate, is to put the results in their own base class:
class Results {
private firstName;
private lastName;
// getters and setters
}
I believe it's possible in JPA (using EntityManager), but I haven't figured out how to do it in Hibernate (using SessionFactory and Session).
I'm trying to learn Hibernate better, and even this "simple" query is proving confusing to know what form Hibernate returns the results, and how to map the results into my own (base) class. So at the end of the DAO routine, I'd do:
List<Results> list = query.list();
returning a List of Results (my base class).

select firstName, lastName from Employee
query.setResultTransformer(Transformers.aliasToBean(MyResults.class));
You can't use above code with Hibernate 5 and Hibernate 4 (at least Hibernate 4.3.6.Final), because of an exception
java.lang.ClassCastException: com.github.fluent.hibernate.request.persistent.UserDto cannot be cast to java.util.Map
at org.hibernate.property.access.internal.PropertyAccessMapImpl$SetterImpl.set(PropertyAccessMapImpl.java:102)
The problem is that Hibernate converts aliases for column names to upper case — firstName becomes FIRSTNAME. And it try to find a getter with name getFIRSTNAME(), and setter setFIRSTNAME() in the DTO using such strategies
PropertyAccessStrategyChainedImpl propertyAccessStrategy = new PropertyAccessStrategyChainedImpl(
PropertyAccessStrategyBasicImpl.INSTANCE,
PropertyAccessStrategyFieldImpl.INSTANCE,
PropertyAccessStrategyMapImpl.INSTANCE
);
Only PropertyAccessStrategyMapImpl.INSTANCE suits, in opinion of Hibernate, well. So after that it tries to do conversion (Map)MyResults.
public void set(Object target, Object value, SessionFactoryImplementor factory) {
( (Map) target ).put( propertyName, value );
}
Don't know, it is a bug or feature.
How to solve
Using aliases with quotes
public class Results {
private String firstName;
private String lastName;
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}
String sql = "select firstName as \"firstName\",
lastName as \"lastName\" from Employee";
List<Results> employees = session.createSQLQuery(sql).setResultTransformer(
Transformers.aliasToBean(Results.class)).list();
Using a custom result transformer
Another way to solve the problem — using a result transformer that ignores method names case (treat getFirstName() as getFIRSTNAME()). You can write your own or use FluentHibernateResultTransformer. You will not need to use quotes and aliases (if you have column names equal to DTO names).
Just download the library from the project page (it doesn't need additional jars): fluent-hibernate.
String sql = "select firstName, lastName from Employee";
List<Results> employees = session.createSQLQuery(sql)
.setResultTransformer(new FluentHibernateResultTransformer(Results.class))
.list();
This transformer can be used for nested projections too: How to transform a flat result set using Hibernate

See AliasToBeanResultTransformer:
Result transformer that allows to transform a result to a user specified class which will be populated via setter methods or fields matching the alias names.
List resultWithAliasedBean = s.createCriteria(Enrolment.class)
.createAlias("student", "st")
.createAlias("course", "co")
.setProjection( Projections.projectionList()
.add( Projections.property("co.description"), "courseDescription" )
)
.setResultTransformer( new AliasToBeanResultTransformer(StudentDTO.class) )
.list();
StudentDTO dto = (StudentDTO)resultWithAliasedBean.get(0);
Your modified code:
List resultWithAliasedBean = s.createCriteria(Employee.class, "e")
.setProjection(Projections.projectionList()
.add(Projections.property("e.firstName"), "firstName")
.add(Projections.property("e.lastName"), "lastName")
)
.setResultTransformer(new AliasToBeanResultTransformer(Results.class))
.list();
Results dto = (Results) resultWithAliasedBean.get(0);
For native SQL queries see Hibernate documentation:
13.1.5. Returning non-managed entities
It is possible to apply a ResultTransformer to native SQL queries, allowing it to return non-managed entities.
sess.createSQLQuery("SELECT NAME, BIRTHDATE FROM CATS")
.setResultTransformer(Transformers.aliasToBean(CatDTO.class))
This query specified:
the SQL query string
a result transformer
The above query will return a list of CatDTO which has been instantiated and injected the values of NAME and BIRTHNAME into its corresponding properties or fields.

You need to use a constructor and in the hql use new. I let you the code example taken from this question: hibernate HQL createQuery() list() type cast to model directly
class Result {
private firstName;
private lastName;
public Result (String firstName, String lastName){
this.firstName = firstName;
this.lastName = lastName;
}
}
then your hql
select new com.yourpackage.Result(employee.firstName,employee.lastName)
from Employee
and your java (using Hibernate)
List<Result> results = session.createQuery("select new com.yourpackage.Result(employee.firstName,employee.lastName) from Employee").list();

YMMV but I've found that the key factor is you must make sure to alias every field in your SELECT clause with the SQL "AS" keyword. I've never had to use quotes around the alias names. Also, in your SELECT clause use the case and punctuation of the actual columns in your database and in the aliases use the case of the fields in your POJO. This has worked for me in Hibernate 4 and 5.
#Autowired
private SessionFactory sessionFactory;
...
String sqlQuery = "SELECT firstName AS firstName," +
"lastName AS lastName from Employee";
List<Results> employeeList = sessionFactory
.getCurrentSession()
.createSQLQuery(sqlQuery)
.setResultTransformer(Transformers.aliasToBean(Results.class))
.list();
If you have multiple tables you can use table aliases in the SQL as well. This contrived example with an additional table named "Department" uses more traditional lower case and underscores in database field names with camel case in the POJO field names.
String sqlQuery = "SELECT e.first_name AS firstName, " +
"e.last_name AS lastName, d.name as departmentName" +
"from Employee e, Department d" +
"WHERE e.department_id - d.id";
List<Results> employeeList = sessionFactory
.getCurrentSession()
.createSQLQuery(sqlQuery)
.setResultTransformer(Transformers.aliasToBean(Results.class))
.list();

java.lang.ClassCastException: "CustomClass" cannot be cast to java.util.Map.
This issue appears when the columns specified in SQL Query doesn't match with the columns of the mapping class.
It may be due to:
Non-matching casing of column name or
The column names are not matching or
column exist in query but missing in class.

JPQL case from hibernate 5.4:
Query<Employee> queryList = session.createQuery("select new xxx.xxx.Employee(e.firstName,e.lastName) from Employee e", Employee.class);
List<Employee> list = queryList.list();
Query<Long> queryCount = session.createQuery("select count(*) from Employee", Long.class);
Long count = queryCount.getSingleResult();
The select statement in JPQL is exactly the same as for HQL except that JPQL requires a select_clause, whereas HQL does not.
setResultTransformer #Deprecated It should not be used
more on Hibernate_User_Guide.html#hql-select

In case you have a native query, all answers here use deprecated methods for newer versions of Hibernate, so if you are using 5.1+ this is the way to go:
// Note this is a org.hibernate.query.NativeQuery NOT Query.
NativeQuery query = getCurrentSession()
.createNativeQuery(
"SELECT {y.*} , {x.*} from TableY y left join TableX x on x.id = y.id");
// This maps the results to entities.
query.addEntity("x", TableXEntity.class);
query.addEntity("y", TableYEntity.class);
query.list()

Below is a result transformer that ignores case:
package org.apec.abtc.dao.hibernate.transform;
import java.lang.reflect.Field;
import java.util.Arrays;
import java.util.List;
import org.hibernate.HibernateException;
import org.hibernate.property.access.internal.PropertyAccessStrategyBasicImpl;
import org.hibernate.property.access.internal.PropertyAccessStrategyChainedImpl;
import org.hibernate.property.access.internal.PropertyAccessStrategyFieldImpl;
import org.hibernate.property.access.internal.PropertyAccessStrategyMapImpl;
import org.hibernate.property.access.spi.Setter;
import org.hibernate.transform.AliasedTupleSubsetResultTransformer;
/**
* IgnoreCaseAlias to BeanResult Transformer
*
* #author Stephen Gray
*/
public class IgnoreCaseAliasToBeanResultTransformer extends AliasedTupleSubsetResultTransformer
{
/** The serialVersionUID field. */
private static final long serialVersionUID = -3779317531110592988L;
/** The resultClass field. */
#SuppressWarnings("rawtypes")
private final Class resultClass;
/** The setters field. */
private Setter[] setters;
/** The fields field. */
private Field[] fields;
private String[] aliases;
/**
* #param resultClass
*/
#SuppressWarnings("rawtypes")
public IgnoreCaseAliasToBeanResultTransformer(final Class resultClass)
{
if (resultClass == null)
{
throw new IllegalArgumentException("resultClass cannot be null");
}
this.resultClass = resultClass;
this.fields = this.resultClass.getDeclaredFields();
}
#Override
public boolean isTransformedValueATupleElement(String[] aliases, int tupleLength) {
return false;
}
/**
* {#inheritDoc}
*/
#Override
public Object transformTuple(final Object[] tuple, final String[] aliases)
{
Object result;
try
{
if (this.setters == null)
{
this.aliases = aliases;
setSetters(aliases);
}
result = this.resultClass.newInstance();
for (int i = 0; i < aliases.length; i++)
{
if (this.setters[i] != null)
{
this.setters[i].set(result, tuple[i], null);
}
}
}
catch (final InstantiationException | IllegalAccessException e)
{
throw new HibernateException("Could not instantiate resultclass: " + this.resultClass.getName(), e);
}
return result;
}
private void setSetters(final String[] aliases)
{
PropertyAccessStrategyChainedImpl propertyAccessStrategy = new PropertyAccessStrategyChainedImpl(
PropertyAccessStrategyBasicImpl.INSTANCE,
PropertyAccessStrategyFieldImpl.INSTANCE,
PropertyAccessStrategyMapImpl.INSTANCE
);
this.setters = new Setter[aliases.length];
for (int i = 0; i < aliases.length; i++)
{
String alias = aliases[i];
if (alias != null)
{
for (final Field field : this.fields)
{
final String fieldName = field.getName();
if (fieldName.equalsIgnoreCase(alias))
{
alias = fieldName;
break;
}
}
setters[i] = propertyAccessStrategy.buildPropertyAccess( resultClass, alias ).getSetter();
}
}
}
/**
* {#inheritDoc}
*/
#Override
#SuppressWarnings("rawtypes")
public List transformList(final List collection)
{
return collection;
}
#Override
public boolean equals(Object o) {
if ( this == o ) {
return true;
}
if ( o == null || getClass() != o.getClass() ) {
return false;
}
IgnoreCaseAliasToBeanResultTransformer that = ( IgnoreCaseAliasToBeanResultTransformer ) o;
if ( ! resultClass.equals( that.resultClass ) ) {
return false;
}
if ( ! Arrays.equals( aliases, that.aliases ) ) {
return false;
}
return true;
}
#Override
public int hashCode() {
int result = resultClass.hashCode();
result = 31 * result + ( aliases != null ? Arrays.hashCode( aliases ) : 0 );
return result;
}
}

Writing (exist this type of Challenges working with hibernate)
Custom Queries
Custom Queries with Optional Parameters
Mapping Hibernate Custom query results to Custom class.
I am not saying about custom EntityRepository interface which extends JpaRepository on SpringBoot which you can write custom Query with #Query -> here you can't write query with optional params
e.g. if param is null don't append it in query string. And you can use Criteria api of hibernate but it not recommended in their documentation because of performance issue...
But exist simple and error prone and performance good way...
Write your own QueryService class which are methods will get
string(answer for first and second problem) sql and will map result to
Custom class (third problem) with it's any association #OneToMany, #ManyToOne ....
#Service
#Transactional
public class HibernateQueryService {
private final Logger log = LoggerFactory.getLogger(HibernateQueryService.class);
private JpaContext jpaContext;
public HibernateQueryService(JpaContext jpaContext) {
this.jpaContext = jpaContext;
}
public List executeJPANativeQuery(String sql, Class entity){
log.debug("JPANativeQuery executing: "+sql);
EntityManager entityManager = jpaContext.getEntityManagerByManagedType(Article.class);
return entityManager.createNativeQuery(sql, entity).getResultList();
}
/**
* as annotation #Query -> we can construct here hibernate dialect
* supported query and fetch any type of data
* with any association #OneToMany and #ManyToOne.....
*/
public List executeHibernateQuery(String sql, Class entity){
log.debug("HibernateNativeQuery executing: "+sql);
Session session = jpaContext.getEntityManagerByManagedType(Article.class).unwrap(Session.class);
return session.createQuery(sql, entity).getResultList();
}
public <T> List<T> executeGenericHibernateQuery(String sql, Class<T> entity){
log.debug("HibernateNativeQuery executing: "+sql);
Session session = jpaContext.getEntityManagerByManagedType(Article.class).unwrap(Session.class);
return session.createQuery(sql, entity).getResultList();
}
}
Use case - you can write any type condition about query params
#Transactional(readOnly = true)
public List<ArticleDTO> findWithHibernateWay(SearchFiltersVM filter){
Long[] stores = filter.getStores();
Long[] categories = filter.getCategories();
Long[] brands = filter.getBrands();
Long[] articles = filter.getArticles();
Long[] colors = filter.getColors();
String query = "select article from Article article " +
"left join fetch article.attributeOptions " +
"left join fetch article.brand " +
"left join fetch article.stocks stock " +
"left join fetch stock.color " +
"left join fetch stock.images ";
boolean isFirst = true;
if(!isArrayEmptyOrNull(stores)){
query += isFirst ? "where " : "and ";
query += "stock.store.id in ("+ Arrays.stream(stores).map(store -> store.toString()).collect(Collectors.joining(", "))+") ";
isFirst = false;
}
if(!isArrayEmptyOrNull(brands)){
query += isFirst ? "where " : "and ";
query += "article.brand.id in ("+ Arrays.stream(brands).map(store -> store.toString()).collect(Collectors.joining(", "))+") ";
isFirst = false;
}
if(!isArrayEmptyOrNull(articles)){
query += isFirst ? "where " : "and ";
query += "article.id in ("+ Arrays.stream(articles).map(store -> store.toString()).collect(Collectors.joining(", "))+") ";
isFirst = false;
}
if(!isArrayEmptyOrNull(colors)){
query += isFirst ? "where " : "and ";
query += "stock.color.id in ("+ Arrays.stream(colors).map(store -> store.toString()).collect(Collectors.joining(", "))+") ";
}
List<Article> articles = hibernateQueryService.executeHibernateQuery(query, Article.class);
/**
* MapStruct [http://mapstruct.org/][1]
*/
return articles.stream().map(articleMapper::toDto).collect(Collectors.toList());
}

jpa native query control entity(part 3)

Retrieve company table
GetEntity.java
String table = "company";
String q = "select * from " +table;
Query query = em.createNativeQuery(q, Company.class);
List<Company> list = query.getResultList();
...
Retrieve staff table
GetEntity.java
String table = "staff";
String q = "select * from " +table;
Query query = em.createNativeQuery(q, Staff.class);
List<Staff> list = query.getResultList();
...
My questions is how do I control the ? from the following:
em.createNativeQuery(q, ?);
List<?> list = q.getResultList();
Any ideas or suggestion?

Another option is to pass the Class entityClass as an argument to your find method and then you can try and derive table name from entityClass by using reflection and use the entityClass as the type argument to your createNativeQuery method.
Hope this helps!