I have a class as following that need to retrieve from DB using Hibernate.
The problem is my class has multiple members and majority of them are classes, how can I retrieve them?
#Entity
public class Student {
#Id
long id;
String name;
String fname;
#OneToMany
List<Course> courses;
#ManyToOne
Dealer dealer;
...
}
#Entity
public class Dealer {
#Id
long id;
String name;
#OneToMany(fetch = FetchType.LAZY, mappedBy = "cr.dealer", cascade = CascadeType.ALL)
Set<Car> cars = new HashSet<Cars>(0);
..
}
I need to retrieve student id 1 and all its courses, its dealer and list of dealers' cars.
My projection is as following but it does not return anything.
...
.setProjection(Projections.projectionList()
.add(Projections.property("friends.cars").as("cars")
...
// Projection is not needed, Hibernate will load child values as shown below
Student student = session.get(Student.class);
List<Course> courses = student.getCourses();
Dealer dealer = student.getDealer();
// If u want records only where child records are present, u can use LEFT_OUTER_JOIN
Criteria criteria = getHibernateSession().createCriteria(Student.class);
criteria.createAlias("Course", "Course", JoinType.LEFT_OUTER_JOIN);
// If u want to use Projections for performance, u have to add each and every column in projection
Criteria criteria = getHibernateSession().createCriteria(A.class);
criteria.createAlias("b", "b", JoinType.INNER_JOIN);
criteria.createAlias("b.r", "b.r", JoinType.INNER_JOIN);
criteria.createAlias("b.c", "b.c", JoinType.LEFT_OUTER_JOIN);
ProjectionList projectionList = Projections.projectionList();
projectionList.add(Projections.groupProperty("column1"));
projectionList.add(Projections.property("column2"));
projectionList.add(Projections.property("column3"));
criteria.setProjection(projectionList);
criteria.setResultTransformer(Transformers.aliasToBean(Table.class));
Because you have a List of Courses and a Set of Cars, you can simply fetch the whole graph in a single query:
select s
from Student s
left join fetch s.courses
left join fetch s.dealer d
left join fetch d.cars
where s.id = :id
Because you are fetching two collections, this query will generate a Cartesian Product, so you need to make sure that the selected children collections don't have too many entries.
If you don;t want to run into a Cartesian product, you can simply run this query:
select s
from Student s
left join fetch s.courses
left join fetch s.dealer d
where s.id = :id
and then you access the dealer.cars to fetch that collection with a separate query:
Student s = ...;
s.getDealer().getCars().size();
If high performences are not a concern, then you should let Hibernate do his work.
Just use the getters of you entities.
For exemple:
Student student1 = session.get(Student.class, 1L);
List<Course> courses = student1.getCourses();
Dealer dealer = student1.getDealer();
Set<Car> cars = dealer.getCars();
I am not sure if you can use QueryOver but it would be very easy for these kind of tasks.
Student student = null;
Dealer dealer = null;
Course course = null;
Car car = null;
var myStudent = Session.QueryOver<Student>(() => student)
.Left.JoinQueryOver(() => student.courses, () => courses)
.Left.JoinQueryOver(() => student.dealer, () => dealer)
.Left.JoinQueryOver(() => dealer.cars, () => car)
.SelectList(list => list
.Select(() => student.Name)
.Select(() => student.Age)
.Select(() => courses.Description)
.Select(() => dealer.locaiton)
.Select(() => car.Model))
.TransformUsing(Transformers.AliasToBean<StudentModel>())
.List<StudentModel>().AsQueryable();
Create a StudentModel DTO to have the results. This is just a hint to start with, you can modify this according to your requirement. I hope this will work. :)
Related
I'm beginner at Hibernate and I wan't to figure out some mechanisms.
I have entity:
#Entity
#Table(name = "dish")
public class Dish implements Serializable {
#ManyToMany(fetch = FetchType.LAZY)
private List<Ingredient> ingredients;
#ManyToOne(fetch = FetchType.LAZY)
private Category category;
}
And repository with such method:
#Query("select d from Dish d join fetch d.ingredients")
Set<Dish> getDishesWithIngredientsAndCategory();
And I noticed, that I'm retrieving by this method only Dishes, that have associated ingredients. I have no idea how to get all Dishes, even that haven't ingredients?
And second question is: is it possible to combine in one #Query fetch two columns? Something like:
#Query("select d from Dish d join fetch d.ingredients, d.category")
I tried to use such query, but I'm receiving QuerySelectionException: "d.category is not mapped".
That I'm retrieving by this method only Dishes, that have associated
ingredients.
Use Left Join instead of join: #Query("select d from Dish d left join fetch d.ingredients")
And second question is: is it possible to combine in one #Query fetch
two columns?
You can try this:
#Query("select d from Dish d join fetch d.ingredients join fetch d.category")
I am having difficulty writing a HQL query to select ONLY the caseid, title, and caseStatus fields from my Cases entity. The cases returned have to be distinct based on caseid. I do not want the name and userid fields to be included. I also do not want to use Lazy fetching for caseid, title, and caseStatus fields. Note that the caseStatus field is a one-to-many List. Below are the entities. The getters/setters are omitted to save space.
#Entity
#Table(name = "Cases")
public class Cases {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "caseid", nullable = false)
private Integer caseid;
private Integer userid;
private String name;
private String title;
#OrderBy("caseStatusId DESC")
#OneToMany(mappedBy = "cases", fetch = FetchType.EAGER)
private List<CaseStatus> caseStatus;
}
#Entity
#Table(name = "CaseStatus")
public class CaseStatus {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "caseStatusId", nullable = false)
private Integer caseStatusId;
private String info;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "caseid")
private Cases cases;
}
My goal is to retrieve a distinct List<Cases> or List<Object[]> of the Cases entity containing only caseid, title, and a List<CaseStatus>. The List<CaseStatus> will contain CaseStatus objects with all of its fields populated.
public List<Object[]> getCases(String title) {
TypedQuery<Object[]> q = em.createQuery("select distinct c.caseid, c.title, cs "
+ "FROM Cases c join c.caseStatus cs "
+ "where c.title like :title", Object[].class);
q.setParameter("title", "%" + title + "%");
List<Object[]> results = q.getResultList();
return results;
}
The above method is close, but not correct because rather than returning a List<CaseStatus> in one of the indexes, it is only returning a single CaseStatus entity.
For example, if my DB contains a single Case with a List<CaseStatus> having a size of n for example, the results will be similar to the example below:
Example of results I'm getting now. Not correct:
List<Object[]> index 0:
Contains an Object[] where:
Object[0] = {some caseid}
Object[1] = {some title}
Object[2] = {1st CaseStatus}
List<Object[]> index 1:
Contains an Object[] where:
Object[0] = {same caseid as the one found in index 0 above}
Object[1] = {same title as the one found in index 0 above}
Object[2] = {2nd CaseStatus}
...
List<Object[]> index n-1:
Contains an Object[] where:
Object[0] = {same caseid as all the previous}
Object[1] = {same title as all the previous}
Object[2] = {nth CaseStatus}
Example of results I hope to achieve:
List<Object[]> index 0:
Contains an Object[] where:
Object[0] = {unique caseid}
Object[1] = {some title}
Object[2] = List<CaseStatus> with size of n
Updated the question. Instead of name, title, and List<CaseStatus>, the fields I want to retrieve are caseid, title, and List<CaseStatus>. caseid is the primary key of Cases.
I found various threads Select Collections with HQL - hibernate forum and Select collections with HQL - stackoverflow. It's pretty much the problem I ran into. Looks like no one found a solution in these threads.
Hibernates a bit confused about the query; in HQL do your join like this (apologies, I've not been able to test before posting due to wonky computer, but you should get the idea)
select distinct c from Cases c left join fetch c.caseStatus cs where....
the "fetch" makes it eager. Note that this will return an array of type Cases. You where clauses look about right.
In fact HQL is fully object-oriented and uses your classes structure in the Query, so by writing c.caseStatus HQL expects that your Cases class has a caseStatus property, which is wrong because it's a collection.
If you take a look at Hibernate HQL documentation you can see that:
Compared with SQL, however, HQL is fully object-oriented and understands notions like inheritance, polymorphism and association.
I think what you need to do here is to change your query so it matches your classes structures:
Query q = em.createQuery("select distinct c.name, c.title, cs.caseStatus FROM Cases c left join c.caseStatus where "
+ "c.name like :name and "
+ "c.title like :title");
Correct syntax should be
TypedQuery<Object[]> q = em.createQuery("select c.name, c.title, cs FROM Cases c "
+ "join c.caseStatus cs where "
+ "c.name = :name and "
+ "c.title = :title", Object[].class);
Return type will be List<Object[]>, where in first index of Object[] is c.name, second is c.title and third is associated caseStatus entity. It is possible to query for multiple instances (rows).
We need JOIN because relationship between CaseStatus and Case is mapped via collection.
SELECT cs
FROM Case c JOIN c.cases cs;
Why don't you just use
Query q = em.createQuery("select distinct c from Cases c where "
+ "c.name like :name and "
+ "c.title like :title");
Just try this. This may be a naive approach but should be able to solve the problem. You may be getting more fields than you required but the return type would be list of Cases.
I have a database table Communications with type, value and a foreign key as index that maps back to a Person table declared as follows:
#Table(name = 'communication', schema = 'schema')
#org.hibernate.annotations.Table(appliesTo = 'communication', indexes = {
#Index(name = "idx_communication_person_id", columnNames = { "person_id" })
}
)
And the Person object maps to this as:
#OneToMany(fetch = LAZY, cascade = ALL, orphanRemoval = true)
#JoinColumn(name = "person_id")
#OrderColumn
#Index(name = "idx_communication_person_id")
private final List<Communication> communications
Now I want to create a HQL query with Hibernate, that selects based on this index colum, like:
WHERE person.id in ( SELECT c.person_id FROM Communication c WHERE c.type = 3 AND c.value = 'john.doe#server.com' )
That doesn't work, because HQL doesn't know c.person_id at this point, because index columns are in general unknown to HQL.
How do I properly address the index in HQL, or if that is not possible: how do I write the statement to archive the same as the native-like query above?
EDIT: For performance reasons there must not be a JOIN in any form.
I think you need something like this:
SELECT p.* FROM person p
JOIN p.communication c
WHERE c.type = 3 AND c.value = 'john.doe#server.com'
That doesn't work, because HQL doesn't know c.person_id at this point, because index columns are in general unknown to HQL.
This doesn't make much sense to me.
If you want to have an HQL statement that returns a list of identifiers for Person based on some criteria, you can easily do it much like how your SQL statement is written.
SELECT p.id
FROM Communication c JOIN FETCH c.person p
WHERE c.type = :communicationType
AND c.value = :emailAddress
If you actually want persons, just write the query to select c.person rather than p.id in order to hydrate all Persons. In the following, the query allows you to specify a person identifier on the predicate if needed.
SELECT c.person
FROM Communication c JOIN FETCH c.person p
WHERE c.person.id = :personId
AND c.type = :communicationType
AND c.value = :emailAddress
UPDATE
If you don't want to use any joins, then simply expose the personId as a numeric value on your Communication entity without any association mappings.
public class Communication {
#Column(name = "personId", nullable = false, insertable = false, updatable = false)
private Long personId;
}
You should then be able to issue a query such as:
SELECT c.personId
FROM Communcation c
WHERE c.type = :communicationType
AND c.value = :emailAddress
I have the following situation:
#Entity
public class Period
{
String Name;
}
#Entity
public class Bill
{
Period period;
#OneToMany(mappedBy = "bill", fetch = FetchType.LAZY)
private List<Entry> entry = new ArrayList<Entry>(0);
}
#Entity
public class Entry
{
#NotNull
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "BILL_ID", nullable = false)
Bill bill;
String text;
BigDecimal amount;
}
So what I need is to fetch all the data in a single query, either with the root being the Bill or the Entry using JPA 2.0 criteria (with Hibernate behind). I've read few posts about this problem HERE and HERE and it seems that I can't use subqueries in the result or fetch data two levels deep.
EDIT: To make my problem more clear: When I use Entry as root, I can't fetch Period and when I use Bill as root I can't fetch all other tables in Entry. Also I can't use eager fetch because there are other use cases that need those tables.
Are there any other ways to do this?
Thanks!
To fetch data from association, you use left join fetch clauses:
select distinct b from Bill b
left join fetch b.period
left join fetch b.entry
where b...
or
select distinct e from Entry e
left join fetch e.bill b
left join fetch b.period
where e...
Regarding Criteria, its fetch() method returns a Fetch, which itself has a method fetch() returning a Fetch(), which itself has a method fetch() returning a Fetch, etc. So yes, its supports as many levels you want.
consider the following schema
#Entity
Class employee{
#OneToMany()
List<employee> manaagedEmps;
#OneToOne
employee manager;
}
how to write a query that get all the managed employee for a certain manager , direct(the list of managedEmps) and indirect (managed by managed employee).
It seems that JPA does not support recursive queries. Recently I solved the smilar problem by adding "path" field of type ltree (postgresql). Path is generated by adding id separated by dot to path of parent and path of root nodes is just id. With that field you are able to query subtree (direct and indirect employees) of some node (manager):
SELECT * FROM nodes WHERE path ~ '*.42.*{1,}'; /* for path of type ltree */
SELECT * FROM nodes WHERE path LIKE '%.42.%'; /* for path of type varchar */
The following JPQL query returns flat list of subs for employee with id 2.
List<Employee> subs = em.createQuery(
"SELECT e FROM Employee e LEFT JOIN FETCH e.subs WHERE e.path LIKE '%.' || ?1 || '.%'",
Employee.class
).setParameter(1, '2').getResultList();
//Returns a list of the managed employee of the manager with the specified ID.
#NamedQuery(name="queryName", query="SELECT p.managedEmps FROM employee p WHERE p.manager.uuid = :uuid")
I am using postgresql here.
I did this through native query like this:
Suppose following entity
#Entity
#Table(name = "employee")
public class Employee {
#Id
private Long id;
#ManyToOne
#JoinColumn(name = "parent_id")
private Employee parent;
}
Now, following query can be used to get all childs and sub childs under one manager recursively:
public interface IEmployeeRepository extends JpaRepository<Employee, Long> {
#Query(value = "with recursive subordinates as ("
+ " select e1.id as id, e1.parent_id as parent from employee e1 where e1.parent_id = :parentId"
+ " union"
+ " select e2.id, e2.parent_id from employee e2"
+ " inner join subordinates s on (s.id = e2.parent_id)"
+ " ) select * from subordinates", nativeQuery = true)
Collection<Employee2> getChilds(#Param("parentId") Long parentId);
public static interface Employee2 {
Long getId();
Long getParent();
}
}
Now, you have to convert this result Collection into List in your service layer. That's it.
References:
postgres recursive queries
Jpa Projections to get result
Hope this helps.
I usually prefer to offer some code, but in this case I think the article itself does a better job of explaining.