I am using JPA Specification , need to select specific columns only.
This is the code:
Specification<Item> spec = (root, query, builder) -> {
query.select(root.get("Id"));
Predicate predicate = builder.equal(root.get("Id"), "12345");
return predicate;
};
In log I see that all columns from Item Entity are selected from database.
Is it a bug?
usage:
interface:
public interface Repo extends PagingAndSortingRepository<Item,String>, JpaSpecificationExecutor<Item> {
}
call:
repo.findAll(spec );
JpaSpecificationExecutor is specifically defined to return the entity type. I suspect it is ignoring the .select(root.get("Id")).
Normally you would use Specifications if you have an extremely dynamic set of conditions you are querying by. If you have just a few parameters you need to search by, I would use a derived query, or a named query.
public interface Repo extends PagingAndSortingRepository<Item,String>, JpaSpecificationExecutor<Item> {
#Query("Select i.id from Item i where name=:name")
Long getIdforName(String name);
}
Related
I trying to select from database specific column only
public interface ItemRepository extends PagingAndSortingRepository<Item,String> {
#Query("SELECT i.id FROM Item i where i.id =?1")
Optional<Item> getit(String id);
}
But instead of returning Object Item it returns String (the id value).
How Can I return the object? (I can't add any constructors to it)
p.s. if I use nativeQuery it does work.
This query in JQL can be simpler.
#Query("SELECT i FROM Item i where i.id =?1")
Optional<Item> getit(String id);
Or even
#Query("FROM Item where id =?1")
Optional<Item> getit(String id);
However, since you are already using JPA, you don't need to define any method with a #Query annotation.
findById is already defined.
Optional<Item> itemOpt = itemRepository.findById(id);
I have multiple aggregate classes, such as Request, Scribe, Candidate, and Exam.
Sample schema:
Request (id, scribe_id, candidate_id, exam_id, status)
Scribe (id, name)
Candidate (id, name)
Exam (id, name, schedule)
As you can see, Request table has references to Scribe, Candidate, and Exam tables.
For one of the requirements, I need to return all requests based on a condition by including all the corresponding details of scribe, candidate, and exam.
For this, the query in my repository class will be similar to the following:
SELECT r.id, r.status, c.name, s.name,
e.schedule, e.name
FROM request r
JOIN candidate c ON r.candidate=c.id
JOIN scribe s ON r.scribe=s.id
JOIN exam e ON r.exam=e.id
WHERE <some-condition>
Now, is there a way to map the result of this query directly to a custom Java object and return the same in Spring Data JDBC?
I believe another alternative is to use the Spring JDBC template.
Curious, any out-of-the-box support from Spring Data JDBC?
Thanks.
I am able to return custom Java object by setting rowMapperClass value of org.springframework.data.jdbc.repository.query.Query annotation. For this need to define RowMapper for custom Java object.
Changes look similar to the following:
public class RequestResourceRowMapper implements RowMapper<RequestResource> {
#Override
public RequestResource mapRow(ResultSet resultSet, int rowNumber) throws SQLException { ... }
}
In repository class, need to set rowMapper value.
#Query(value = """
SELECT r.id, r.status, c.name, s.name,
e.schedule, e.name
FROM request r
JOIN candidate c ON r.candidate=c.id
JOIN scribe s ON r.scribe=s.id
JOIN exam e ON r.exam=e.id
WHERE <some-condition>
""",
rowMapperClass = RequestResourceRowMapper.class)
List<RequestResource> searchRequestResources(...);
This could have even been possible without using a custom row mapper as well, but in that case, you will have to assign different names to the columns across the tables. You could have defined a simple class and defined all the fields in there and for mapping the java fields with the corresponding columns in the table, you could have used the #Column attributes example:
public class RequestData {
#Column("id")
private Integer requestId;
#Column("scribe_id")
private String scribeId;
#Column("candidate_id")
private Integer candidateId;
#Column("scribe_name")
private String scribeName;
#Column("candidate_name")
private String candidateName;
#Column("exam_name")
private String examName;
#Column("exam_schedule")
private String examSchedule;
}
However, for such case, you need to have different column names across the schema's which might not be possible in your case as you have same column names in multiple schemas.
Is there a recommended way to go about dealing with documents that don't have the _class field with spring-data-couchbase( if there is one)? Trying it simply just throws an exception as expected.
Edit: Apologies if this was a bit too vague, let me add a bit more context.
I want to fetch data from couchbase for some student by name, let's say . The repository looks something like -
#Repository
public interface StudentRepository extends CouchbaseRepository {
Optional<StudentDocument> findByName(String name);
}
Now the documents in couchbase don't have the _class field OR say if we are entering a different "key" and "value" for _class field as we don't want to rely on it, so this method fails. I sort of hacked a workaround for this using -
`
#Override
public Student getStudent(String name) {
N1qlQuery query = N1qlQuery.simple(String.format("select *, META().id AS _ID, META().cas AS _CAS" +
" from student where name = \'%s\';", name));
return Optional.ofNullable(studentRepository.getCouchbaseOperations()
.findByN1QL(query, StudentWrapper.class)
.get(0))
.map(StudentWrapper::getStudent)
.orElseGet(() -> {
throw new HttpClientErrorException(HttpStatus.NOT_FOUND);
});
}
`
I was wondering if there is an alternate way of achieving this
While using Spring spEL, Couchbase will automatically include the _class (or whatever attribute you have defined as your type) for you:
public interface AreaRepository extends CouchbaseRepository<Area, String> {
//The _class/type is automatically included by Couchbase
List<Area> findByBusinessUnityIdAndRemoved(String businessId, boolean removed);
}
However, if you want to use N1QL, you have to add the #{#n1ql.filter} :
public interface BusinessUnityRepository extends CouchbaseRepository<BusinessUnity, String>{
#Query("#{#n1ql.selectEntity} where #{#n1ql.filter} and companyId = $2 and $1 within #{#n1ql.bucket}")
BusinessUnity findByAreaRefId(String areaRefId, String companyId);
}
the #{#n1ql.filter} will automatically add the filter by type for you.
public List<Series> findSeries(int period, String fieldname, int num) {
TypedQuery<Series> query = em.createQuery(
"select s from Series s where s.period = ?1 order by ?2",
Series.class);
query.setParameter(1, period);
query.setParameter(2, fieldname);
query.setMaxResults(num);
return query.getResultList();
}
This is the method I am using. I think order by isn't even getting executed, it doesn't give any error even when I pass incorrect fieldname.
When it comes to dynamic limit and ordering, its best to use PagingAndSortingRepository so now my Repository extends this repository. I can simply use JPA criteria query as below.
If u want to learn more about JPA criteria query i found this very helpful http://docs.spring.io/spring-data/data-jpa/docs/1.0.x/reference/html/#jpa.query-methods.query-creation
#Repository
public interface SeriesRepository extends PagingAndSortingRepository<Series,Long>{
List<Series> findByPeriod(int period, Pageable pageable);
}
And then when I call this method from my dao i can just instantiate PageRequest which is one of the implementation of Pageable. I can add limit and sorting order to this instance.
public List<Series> getSeriesByFilter(int period, String fieldname, int num) {
Sort sort = new Sort(Sort.Direction.ASC, fieldname);
Pageable pageable = new PageRequest(0, num, sort);
return seriesRepo.findByPeriod(period, pageable);
}
You cannot pass variables as column name in order by.
There is a work around which may help you achieve what you are trying.
public List<Series> findSeries(int period, String fieldname, int num) {
String query = "select s from Series s where s.period = "+period+" order by "+fieldname;
return entityManager.createQuery(query).getResultList();
}
Check this question Hibernate Named Query Order By parameter
There are ways to pass column name in order by in ASP, however I am not able to find anything in Spring or JPA.
"Order By" using a parameter for the column name
http://databases.aspfaq.com/database/how-do-i-use-a-variable-in-an-order-by-clause.html
I have a method:
public List<Timetable> getTimetableTableForRegion(String id) {
List<Timetable> timetables;
TypedQuery<Timetable> query = em_read.createQuery("SELECT ..stuff.. where R.id = :id", Timetable.class).setParameter("id", Long.parseLong(id));
timetables = query.getResultList();
return timetables;
}
which returns this:
so, what am I missing in order to return a list of Timetable's?
ok, so, ..stuff.. part of my JPQL contained an inner join to other table. Even through in SELECT there were selected fields just from one table, which was used as type - Timetable, Eclipslink was unable to determine if this fields are part of that entity and instead of returning list of defined entity returned list of Object[].
So in conclusion: Use #OneToMany/#ManyToOne mappings (or flat table design) and query just for ONE table in your JPQL to be able to typize returned entities.
Not sure it might be something is looking for, but I had similar problem and converted Vector to ArrayList like this:
final ArrayList<YourClazz> results = new ArrayList<YourClazz>();;
for ( YourClazzkey : (Vector<YourClazz>) query.getResultList() )
{
results.add(key);
}
i have faced the same problem. and my entity has no one to one or one to many relationship. then also jpql was giving me queryresult as vector of objects. i changed my solution to query to criteria builder. and that worked for me.
code snippet is as below:
CriteriaBuilder builder = this.entityManager.getCriteriaBuilder();
CriteriaQuery<Timetable> criteria = builder.createQuery(Timetable.class);
Root<Enumeration> root = criteria.from(Timetable.class);
criteria.where(builder.equal(root.get("id"), id));
List<Timetable> topics = this.entityManager.createQuery(criteria) .getResultList();
return topics;