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Is there a way to map 1 column of a query to a collection using Spring JPA/Hibernate [duplicate]

I am using Spring JPA to perform all database operations. However I don't know how to select specific columns from a table in Spring JPA?
For example:
SELECT projectId, projectName FROM projects

You can use projections from Spring Data JPA (doc). In your case, create interface:
interface ProjectIdAndName{
String getId();
String getName();
}
and add following method to your repository
List<ProjectIdAndName> findAll();

I don't like the syntax particularly (it looks a little bit hacky...) but this is the most elegant solution I was able to find (it uses a custom JPQL query in the JPA repository class):
#Query("select new com.foo.bar.entity.Document(d.docId, d.filename) from Document d where d.filterCol = ?1")
List<Document> findDocumentsForListing(String filterValue);
Then of course, you just have to provide a constructor for Document that accepts docId & filename as constructor args.

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.

In my situation, I only need the json result, and this works for me:
public interface SchoolRepository extends JpaRepository<School,Integer> {
#Query("select s.id, s.name from School s")
List<Object> getSchoolIdAndName();
}
in Controller:
#Autowired
private SchoolRepository schoolRepository;
#ResponseBody
#RequestMapping("getschoolidandname.do")
public List<Object> getSchool() {
List<Object> schools = schoolRepository.getSchoolIdAndName();
return schools;
}

With the newer Spring versions One can do as follows:
If not using native query this can done as below:
public interface ProjectMini {
String getProjectId();
String getProjectName();
}
public interface ProjectRepository extends JpaRepository<Project, String> {
#Query("SELECT p FROM Project p")
List<ProjectMini> findAllProjectsMini();
}
Using native query the same can be done as below:
public interface ProjectRepository extends JpaRepository<Project, String> {
#Query(value = "SELECT projectId, projectName FROM project", nativeQuery = true)
List<ProjectMini> findAllProjectsMini();
}
For detail check the docs

In my case i created a separate entity class without the fields that are not required (only with the fields that are required).
Map the entity to the same table.
Now when all the columns are required i use the old entity, when only some columns are required, i use the lite entity.
e.g.
#Entity
#Table(name = "user")
Class User{
#Column(name = "id", unique=true, nullable=false)
int id;
#Column(name = "name", nullable=false)
String name;
#Column(name = "address", nullable=false)
Address address;
}
You can create something like :
#Entity
#Table(name = "user")
Class UserLite{
#Column(name = "id", unique=true, nullable=false)
int id;
#Column(name = "name", nullable=false)
String name;
}
This works when you know the columns to fetch (and this is not going to change).
won't work if you need to dynamically decide the columns.

In my opinion this is great solution:
interface PersonRepository extends Repository<Person, UUID> {
<T> Collection<T> findByLastname(String lastname, Class<T> type);
}
and using it like so
void someMethod(PersonRepository people) {
Collection<Person> aggregates =
people.findByLastname("Matthews", Person.class);
Collection<NamesOnly> aggregates =
people.findByLastname("Matthews", NamesOnly.class);
}

I guess the easy way may be is using QueryDSL, that comes with the Spring-Data.
Using to your question the answer can be
JPAQuery query = new JPAQuery(entityManager);
List<Tuple> result = query.from(projects).list(project.projectId, project.projectName);
for (Tuple row : result) {
System.out.println("project ID " + row.get(project.projectId));
System.out.println("project Name " + row.get(project.projectName));
}}
The entity manager can be Autowired and you always will work with object and clases without use *QL language.
As you can see in the link the last choice seems, almost for me, more elegant, that is, using DTO for store the result. Apply to your example that will be:
JPAQuery query = new JPAQuery(entityManager);
QProject project = QProject.project;
List<ProjectDTO> dtos = query.from(project).list(new QProjectDTO(project.projectId, project.projectName));
Defining ProjectDTO as:
class ProjectDTO {
private long id;
private String name;
#QueryProjection
public ProjectDTO(long projectId, String projectName){
this.id = projectId;
this.name = projectName;
}
public String getProjectId(){ ... }
public String getProjectName(){....}
}

Using Spring Data JPA there is a provision to select specific columns from database
---- In DAOImpl ----
#Override
#Transactional
public List<Employee> getAllEmployee() throws Exception {
LOGGER.info("Inside getAllEmployee");
List<Employee> empList = empRepo.getNameAndCityOnly();
return empList;
}
---- In Repo ----
public interface EmployeeRepository extends CrudRepository<Employee,Integer> {
#Query("select e.name, e.city from Employee e" )
List<Employee> getNameAndCityOnly();
}
It worked 100% in my case.
Thanks.

You can use JPQL:
TypedQuery <Object[]> query = em.createQuery(
"SELECT p.projectId, p.projectName FROM projects AS p", Object[].class);
List<Object[]> results = query.getResultList();
or you can use native sql query.
Query query = em.createNativeQuery("sql statement");
List<Object[]> results = query.getResultList();

You can apply the below code in your repository interface class.
entityname means your database table name like projects.
And List means Project is Entity class in your Projects.
#Query(value="select p from #{#entityName} p where p.id=:projectId and p.projectName=:projectName")
List<Project> findAll(#Param("projectId") int projectId, #Param("projectName") String projectName);

It is possible to specify null as field value in native sql.
#Query(value = "select p.id, p.uid, p.title, null as documentation, p.ptype " +
" from projects p " +
"where p.uid = (:uid)" +
" and p.ptype = 'P'", nativeQuery = true)
Project findInfoByUid(#Param("uid") String uid);

You can use the answer suggested by #jombie, and:
place the interface in a separate file, outside the entity class;
use native query or not (the choice depended on your needs);
don't override findAll() method for this purpose but use name of your choice;
remember to return a List parametrized with your new interface (e.g. List<SmallProject>).

Using Native Query:
Query query = entityManager.createNativeQuery("SELECT projectId, projectName FROM projects");
List result = query.getResultList();

public static final String FIND_PROJECTS = "select ac_year_id,ac_year from tbl_au_academic_year where ac_year_id=?1";
#Query(value = FIND_PROJECTS, nativeQuery = true)
public List<Object[]> findByAcYearId(Integer ac_year_id);
this works for me

You can update your JPARepository as below.
#Query("select u.status from UserLogin u where u.userId = ?1 or u.email = ?1 or u.mobile = ?1")
public UserStatus findByUserIdOrEmailOrMobile(String loginId);
Where UserStatus is a Enum
public enum UserStatus
{
New,
Active,
Deactived,
Suspended,
Locked
}

Use:
#Query("SELECT e FROM #{#entityName} e where e.userId=:uid")
List<ClienteEnderecoEntity> findInfoByUid(#Param("uid") UUID uid);

{
"Comments":"Why not using JDBCTemplate",
"Url":"https://www.baeldung.com/spring-jdbc-jdbctemplate"
}

ListJoin and multiselect with criteriaquery with Polymorphism

I was wondering if anyone knows the cause of the Exception being thrown? I have the following entities below. Is it because some Employees returned aren't DriverEmployees and thus do not have routes?
#Entity
public class Employee {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", nullable = false)
private Integer id;
private String name;
}
#Entity
public class DriverEmployee extends Employee {
#OneToMany(fetch = FetchType.LAZY)
private List<Routes> routes;
}
#Entity
public class Routes {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", nullable = false)
private Integer id;
private String name;
private String description;
}
CriteriaQuery<Tuple> criteria = criteriaBuilder.createQuery(Tuple.class);
Root<Employee> employee = criteria.from(Employee.class);
Root<DriverEmployee> driverEmployee = criteriaBuilder.treat(employee, DriverEmployee.class);
ListJoin<DriverEmployee, Routes> routes = driverEmployee.joinList("routes");
// Want routes to be returned as a list in the multiselect.
criteria.multiselect(employee.get("name").alias("name"), routes.alias("routes"));
TypedQuery<Tuple> query = em.createQuery(criteria);
query.getResultList().forEach((t) -> {
process(t.get("name", String.class));
processList(t.get("routes", List.class).size());
});
The error I'm receiving is below. Anyone know how I can get the following to run successfully?
Caused by: java.lang.IllegalStateException: No data type for node: org.hibernate.hql.internal.ast.tree.IdentNode
+-[IDENT] IdentNode: 'routes' {originalText=routes}

In this current example you have tuple which contains one object of DriverEmployee and one object of Routes (I recommend you to rename this entity to Route and set #Table(name = "routes"). According to JavaDoc of multiselect():
If the type of the criteria query is CriteriaQuery (i.e., a criteria query object created by either the createTupleQuery method or by passing a Tuple class argument to the createQuery method), a Tuple object corresponding to the arguments of the multiselect method, in the specified order, will be instantiated and returned for each row that results from the query execution.
So it means that you CAN'T make a Tuple like Tuple<DriverEmployee, List<Routes>>
The way how you can reach such behavior of your current query is to do it by yourself. For instance:
your method with criteria:
CriteriaQuery<Tuple> criteria = criteriaBuilder.createQuery(Tuple.class);
Root<Employee> employee = criteria.from(Employee.class);
Root<DriverEmployee> driverEmployee = criteriaBuilder.treat(employee, DriverEmployee.class);
ListJoin<DriverEmployee, Routes> routes = driverEmployee.joinList("routes");
criteria.multiselect(employee.get("name").alias("name"), routes.alias("routes"));
TypedQuery<Tuple> query = em.createQuery(criteria);
List<Tuple> resultList = query.getResultList();
Map<String, List<Routes>> resultMap = getMapFromResultList(resultList);
resultMap.entrySet().forEach((name, routesList) -> {
process(name);
processList(routesList);
});
and the method of obtaining the map:
private Map<String, List<Routes>> getMapFromResultList(List<Tuple> tuples) {
Map<String, List<Routes>> map = new HashMap<>();
tuples.forEach(tuple -> {
String name = tuple.get("name", String.class);
Routes routes = tuple.get("routes", Routes.class);
map.computeIfPresent(name, (key, value) -> {
value.add(routes);
return value;
});
map.computeIfAbsent(name, (key) -> {
List<Routes> routesList = new ArrayList<>();
routesList.add(routes);
return routesList;
});
});
return map;
}

I guess the Hibernate JPA Criteria implememtation doesn't support that. If you really want to use the JPA Criteria API to do this, you are probably out of luck. In JPQL/HQL you could model this like SELECT e.name, r FROM DriverEmployee e LEFT JOIN e.routes r. On top of that you have to extract the values like Andrew Kolesnyk mentioned.
However, this is is the perfect use case for Blaze-Persistence Entity Views.
Blaze-Persitence is a query builder on top of JPA which supports many of the advanced DBMS features on top of the JPA model. I created Entity Views on top of it to allow easy mapping between JPA models and custom interface defined models, something like Spring Data Projections on steroids. The idea is that you define your target structure the way you like and map attributes(getters) via JPQL expressions to the entity model. Since the attribute name is used as default mapping, you mostly don't need explicit mappings as 80% of the use cases is to have DTOs that are a subset of the entity model.
A mapping for your model could look as simple as the following
#EntityView(DriverEmployee.class)
interface EmployeeDto {
#IdMapping
Integer getId();
String getName();
List<RoutesDto> getRoutes();
}
#EntityView(Routes.class)
interface RoutesDto {
#IdMapping
Integer getId();
String getName();
}
Querying is a matter of applying the entity view to a query, the simplest being just a query by id.
EmployeeDto dto = entityViewManager.find(entityManager, EmployeeDto.class, id);
The Spring Data integration allows you to use it almost like Spring Data Projections: https://persistence.blazebit.com/documentation/entity-view/manual/en_US/index.html#spring-data-features and it can also be saved back. Here a sample repository
#Repository
interface EmployeeRepository {
EmployeeDto findOne(Long id);
}
It will only fetch the mappings that you tell it to fetch.
Here you can see an example project: https://github.com/Blazebit/blaze-persistence/tree/master/examples/spring-data-webmvc

hibernate native query complex constructor mapping

Java, Spring Data JPA
I have 2 entities:
class Source {
Integer id;
String name;
}
class Item {
Integer id;
String name;
Integer sourceId;
}
I need statistic native query result like this:
select s.id source_id, s.name source_name, count(i.id) item_count
from source s
left join item i on s.id = i.source_id
group by s.id
And i want to have result in Java object MyResult:
class MyResult {
Source source;
Integer itemCount;
MyResult(Source source, Integer itemCount) {...}
}
The closest solution is using #SqlResultSetMapping like this:
#SqlResultSetMapping(
name = "MyResultMapping",
entities = {
#EntityResult(
entityClass = Source.class,
fields = {
#FieldResult(name = "id", column = "source_id"),
#FieldResult(name = "name", column = "source_name"),
}
),
...
???
}
)
OR
#SqlResultSetMapping(
name = "MyResultMapping",
classes = {
#ConstructorResult(
targetClass = MyResult.class,
columns = {
#ColumnResult(name = "???"),
???
}
)
}
)
With second variant i can use something like this:
MyResult(Integer sourceId, String sourceName, Integer itemsCount) {
this.source = new Source(sourceId, sourceName);
this.itemsCount = itemsCount;
}
but i want it to automate with #SqlResultSetMapping... (because my real objects more complex)

With Spring Data JPA it's better to use projections to achieve you need, for example:
public interface SourceWithItemCount {
Source getSource();
Integer getItemCount();
}
Then in your Source repository create HQL query method, like this:
public interface SourceRepo extends JpaRepository<Source, Integer> {
#Query("select s as source, count(i) like itemCount from Source s left join Item i on i.sourceId = s.id group by s"
List<SourceWithItemCount> getSourcesWithItemCount();
}
Important note is to use aliases for returned values (s as source etc.) it's allows Spring Data JPA to map them to projections properties.
Join on <condition> works from Hibernate version 5.1+ (if I'm not mistaken) so I recommend you to create classic one-to-many relation between your objects, like this, for example:
#Entity
class Source {
#Id private Integer id;
private String name;
#OneToMany #JoinColumn(name = "source_id") private List<Item> items;
}
#Entity
class Item {
#Id private Integer id;
private String name;
}
Then create JPQL query method supported by all versions of Hibernate (and other ORM providers):
#Query("select s as source, count(i) like itemCount from Source s left join s.items i group by s"
List<SourceWithItemCount> getSourcesWithItemCount();

Spring JPA native query with Projection gives "ConverterNotFoundException"

I'm using Spring JPA and I need to have a native query. With that query, I need to get only two fields from the table, so I'm trying to use Projections. It isn't working, this is the error I'm getting:
org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [org.springframework.data.jpa.repository.query.AbstractJpaQuery$TupleConverter$TupleBackedMap] to type [com.example.IdsOnly]
I tried to follow precisely the instructions of that page I linked, I tried to make my query non-native (do I actually need it to be native if I use projections, btw?), but I always get that error.
If I use an interface it works, but the results are proxies and I really need them to be "normal results" that I can turn into json.
So, here's my code. The Entity:
import lombok.Data;
import lombok.NoArgsConstructor;
#Data
#NoArgsConstructor
#Entity
#Table(name = "TestTable")
public class TestTable {
#Id
#Basic(optional = false)
#GeneratedValue(strategy = GenerationType.SEQUENCE)
#Column(name = "Id")
private Integer id;
#Column(name = "OtherId")
private String otherId;
#Column(name = "CreationDate")
#Temporal(TemporalType.TIMESTAMP)
private Date creationDate;
#Column(name = "Type")
private Integer type;
}
The class for the projection:
import lombok.Value;
#Value // This annotation fills in the "hashCode" and "equals" methods, plus the all-arguments constructor
public class IdsOnly {
private final Integer id;
private final String otherId;
}
The Repository:
public interface TestTableRepository extends JpaRepository<TestTable, Integer> {
#Query(value = "select Id, OtherId from TestTable where CreationDate > ?1 and Type in (?2)", nativeQuery = true)
public Collection<IdsOnly> findEntriesAfterDate(Date creationDate, List<Integer> types);
}
And the code that tries to get the data:
#Autowired
TestTableRepository ttRepo;
...
Date theDate = ...
List<Integer> theListOfTypes = ...
...
Collection<IdsOnly> results = ttRepo.findEntriesAfterDate(theDate, theListOfTypes);
Thanks for the help. I really don't understand what I'm doing wrong.

with spring data you can cut the middle-man and simply define
public interface IdsOnly {
Integer getId();
String getOtherId();
}
and use a native query like;
#Query(value = "Id, OtherId from TestTable where CreationDate > ?1 and Type in (?2)", nativeQuery = true)
public Collection<IdsOnly> findEntriesAfterDate(Date creationDate, List<Integer> types);
check out https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#projections

The query should be using a constructor expression:
#Query("select new com.example.IdsOnly(t.id, t.otherId) from TestTable t where t.creationDate > ?1 and t.type in (?2)")
And i dont know Lombok, but make sure there is a constructor that takes the two IDs as parameters.

JPA 2.1 introduces an interesting ConstructorResult feature if you want to keep it native.

You can return list of Object Array (List) as return type of the native query method in repository class.
#Query(
value = "SELECT [type],sum([cost]),[currency] FROM [CostDetails] " +
"where product_id = ? group by [type],[currency] ",
nativeQuery = true
)
public List<Object[]> getCostDetailsByProduct(Long productId);
for(Object[] obj : objectList){
String type = (String) obj[0];
Double cost = (Double) obj[1];
String currency = (String) obj[2];
}

#Query(value = "select isler.saat_dilimi as SAAT, isler.deger as DEGER from isler where isler.id=:id", nativeQuery = true)
List<Period> getById(#Param("id") Long id);
public interface Period{
Long getDEGER();
Long getSAAT();
}
as seen in the example code for native query given above, cast return values to any value like as "SAAT", "DEGER" and then define interface "period" which have getDEGER() and getSAAT(). Even if I have not understand why parameter after get must be uppercase, in lowercase scenario it didn't work properly. ie. interface with getDeger(), getSaat() does not work properly in my case.

Spring JPA Join Efficiency - Create a query for each iteration

I have a simple 2 JPA entities which I have a Join Between them:
Primary entity Country:
public class Country implements Serializable {
#Id
#Column(name = "MCC")
private String mcc;
......
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
#JoinColumn(name = "mcc", referencedColumnName = "mcc")
private List<CountryInfo> countryInfo;
Joint entity CountryInfo:
public class CountryInfo implements Serializable {
#Id
#Column(name = "id")
private Long id;
#Column(name = "mcc")
private String mcc;
#Column(name = "continent")
private String continent;
When I've turned on my configuration to dump the queries being executed, I've noticed that for each Country found, another call is done on the CountryInfo entity with the mcc specified..
This is obviously slow since rather than creating 1 call with a JOIN, it is executing N + 1 queries (where N = count of Country).
I've already seen this tutorial https://zeroturnaround.com/rebellabs/how-to-use-jpa-correctly-to-avoid-complaints-of-a-slow-application/ and changed accordingly but it is still calling N + 1 queries..
Is there a way to overcome this?
EDIT
In order to get the data I have a Repository:
#RepositoryRestResource(exported = false)
public interface CountryRepository extends JpaRepository<E212MCC, Long>,
JpaSpecificationExecutor<E212MCC> {
}
And then call with some specifications:
List<E212MCC> countries = this.countryRepository.findAll(specifications);

Since you are using Specifications you could try with specification that performs fetch join operation (I am assuming that you are using JPA meta model):
private Specification<Country> joinContryInfo() {
return (root, query, cb) -> {
root.fetch(Country_.countryInfo);
// here you can fetch more entities if you need...
return null;
};
}
And then, just add it to your specification object:
Specifications.where(joinCountryInfo())
If you are not using meta model then just replace Country_.countryInfo with "countryInfo" string.
If you are using CountryInfo fields for searching, you can omit joinContryInfo() specification and prepare join and search query in one specification:
private Specification<Country> continentEqual(String param) {
return (root, query, cb) -> {
Join<Country,CountryInfo> join = (Join) root.fetch(Country_.countryInfo);
return cb.equal(join.get(CountryInfo_.continent), addWildCards(param));;
};
}