Given this very simple DTO:
#Entity
public class Employee implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
private String name;
#OneToOne
private Employee boss;
}
I'd like to make a query that gathers all employee names and their boss' id, put in a nice clean POJO:
public class EmployeeInfo {
private String name;
private Long bossId;
public EmployeeInfo(String name, Long bossId) {
this.name = name;
this.bossId = bossId;
}
}
This query should be of use:
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<EmployeeInfo> query = cb.createQuery(EmployeeInfo.class);
Root<Employee> root = query.from(Employee.class);
query.select(
cb.construct(EmployeeInfo.class,
root.get("name").as(String.class),
root.get("boss").get("id").as(Long.class)));
result = em.createQuery(query).getResultList();
When a bossId is present in the employee column this works just fine. But when no boss id is set the record will be completly ignored. So how do i treat this non existing boss relation as null or 0 for the construct/multiselect?
In pure SQL it is easy:
SELECT name, COALESCE(boss_id, 0) FROM EMPLOYEE;
But for the love of god i cannot make the criteria api do this.
cb.construct(EmployeeInfo.class,
root.get("name").as(String.class),
cb.coalesce(root.get("boss").get("id").as(Long.class), 0L)));
The problem is that root.get("boss") generate query with cross join like this from Employee employee, Employee boss where employee.boss.id=boss.id. So records where employee.boss.id is null are ignored.
To solve the problem you should use root.join("boss", JoinType.LEFT) instead of root.get("boss")
Related
I have a question about usage of nested list projection interface. I have two entity (Parent and child) (they have Unidirectional association)
Parent =>
#Table(name = "parent")
#Entity
public class ParentEntity {
#GeneratedValue(strategy = GenerationType.AUTO)
private long id;
private String name;
// other fields........
}
Child =>
#Table(name = "child")
#Entity
public class ChildEntity {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private long id;
#NonNull
private String name;
#NonNull
#ManyToOne(fetch = FetchType.LAZY)
private ParentEntity parent;
// other fields........
}
I have two projection interface for select specific columns.
ParentProjection =>
public interface ParentProjection {
String getName();
Set<ChildProjection> getChild();
}
ChildProjection =>
public interface ChildProjection {
String getId();
String getName();
}
I want to take list of ParentProjection which includes with list of ChildProjection.
Repository query like that =>
#Query("select p.name as name, c as child from ParentEntity p left join ChildEntity as c on p.id = c.parent.id")
List<ParentProjection> getParentProjectionList();
This query works, but it selects all columns of ChildEntity, and map only id, name propeties to ChildProjection. (generated query selects all columns, but i want to select only id and name columns)
How can i select only id and name columns (select specific columns for nested list projection interface) and map to ChildProjection fields (using with #Query) ?
Note: I don't need to use class type projection.
You need to add the OneToMany relation to ParentEntity and annotate with Lazy.
Hope it helps (i have tried this).
How to invoke order by on a joined entity? I am trying to achieve the following with:
select * from person p inner join telephone t on p.id=t.person_id join sim s on s.id=t.sim_id order by s.name DESC
#Entity
public class Person implements Serializable{
#Id
private Long id;
#OneToMany(orphanRemoval = true, mappedBy = "person", fetch = FetchType.LAZY, cascade = CascadeType.PERSIST)
private List<Telephone> telephonesNumber;
#Entity
public class Telephone implements Serializable {
#Id
private String number;
#Id
#ManyToOne()
#JoinColumn(name = "person_id")
private Person person;
#Id
#ManyToOne(cascade = {})
#JoinColumn(name = "sim_id")
private Sim sim;
#Entity
public class Sim implements Serializable {
#Id
private Long id;
#Column(unique = true)
private String name;
I use specification interface, in this example sorting is on the field person.id and it works
public class PersonSpecification implements Specification<Person> {
#Override
public Predicate toPredicate(Root<Person> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
List<Predicate> predicates = new ArrayList<>();
// there is many different conditions for example
// if(someCondition!=null) {
// predicates.add(builder.like(root.get("someProperty"), someValue));
// }
query.groupBy(root.get("id"));
//there I want to order by Sim.name i dont know how
query.orderBy(builder.asc(root.get("phone")));//this works
return builder.and((predicates.toArray(new Predicate[predicates.size()])));
}
I want to order by Sim.name but i dont know how.
In JPA specification you can use:
query.orderBy(builder.asc(root.join("telephonesNumber").get("sim").get("name")));
to sort by sim name.
For more details:
https://en.wikibooks.org/wiki/Java_Persistence/Querying#Joining.2C_querying_on_a_OneToMany_relationship
If you using JPA Query:
#Query("select s from Person p
join p.telephonesNumber t
join t.sim s order
by t.sim.id desc")
It will produce this:
select * from person p
inner join telephone t on p.id=t.person_id
inner join sim s on t.sim_id=s.id
order by t.sim_id desc
For more details:
https://github.com/abhilekhsingh041992/spring-boot-samples/blob/master/jpa/src/main/java/example/springboot/jpa/repository/PersonRepository.java
another way for that would be using Query method:
List<Telephone> findAllByOrderBySimIdAsc();
Look at this findAllByOrderBySimIdAsc
With the code before, you can get all rows from Telephone ordered by Sim Id.
i have two entities Customer and Order (trivial setters and getters excluded)
#Entity
public class Customer {
#GeneratedValue
#Id
private int id;
#OneToMany
List<Order> orderList;
}
#Entity
public class Order {
#GeneratedValue
#Id
private int id;
#ManyToOne
Customer customer;
private boolean paid;
public Order(Customer customer) {
this.customer = customer;
customer.getOrderList().add(this)
}
}
Now i want to set 'paid = true' for all the orders of a given customer
Below query seem to do the trick, but I get a feeling it is innefficient and the fact that i stored the reverse relationship in Customer.orderList hints that there should be some other way to do this.
UPDATE Order o SET o.paid = true WHERE EXISTS
(SELECT c.orderList FROM Customer c WHERE o MEMBER OF c.orderList AND c = :customer)
I'm using container managed transactions, glassfish and javaDb. But I'd prefer if improvements could be done in JPA/JPQL domain and not specific to container or db.
private id; ?? missed field type
Add to #OneToMany annotation,cascade = CascadeType.All
Customer entity = entityManager.find(Customer.class, id)
for (Order order : entity.getOrderList())
{
order.setPaid(true);
}
if you are using cantainer managed transaction then true will be saved to DB
I have the following entities and would like to seek help on how to query for selected attributes from both side of the relationship. Here is my model. Assume all tables are properly created in the db. JPA provider I am using is Hibernate.
#Entity
public class Book{
#Id
private long id;
#Column(nullable = false)
private String ISBNCode;
#ManyToOne(cascade = CascadeType.DETACH, fetch = FetchType.LAZY, optional = false)
private Person<Author> author;
#ManyToOne(cascade = CascadeType.DETACH, fetch = FetchType.LAZY, optional = true)
private Person<Borrower> borrower;
}
#Inheritance
#DiscriminatorColumn(name = "personType")
public abstract class Person<T>{
#Id
private long id;
#OneToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private Info information;
}
#Entity
#DiscriminatorValue(PersonType.Author)
public class Author extends Person<Author> {
private long copiesSold;
}
#Entity
#DiscriminatorValue(PersonType.Borrower)
public class Borrower extends Person<Borrower> {
.....
}
#Entity
public class Info {
#Id
private long id;
#Column(nullable=false)
private String firstName;
#Column(nullable=false)
private String lastName;
......;
}
As you can see, the book table has a many to one relation to Person that is not nullable and Person that is nullable.
I have a requirement to show, the following in a tabular format -
ISBNCode - First Name - Last Name - Person Type
How can I write a JPA query that will allow me to select only attributes that I would want. I would want to get the attributes ISBN Code from Book, and then first and last names from the Info object that is related to Person Object that in turn is related to the Book object. I would not want to get all information from Info object, interested only selected information e.g first and last name in this case.
Please note that the relation between the Borrower and Book is marked with optional=true, meaning there may be a book that may not have been yet borrowed by someone (obviously it has an author).
Example to search for books by the author "Marc":
Criteria JPA Standard
CriteriaQuery<Book> criteria = builder.createQuery( Book.class );
Root<Book> personRoot = criteria.from( Book.class );
Predicate predicate = builder.conjunction();
List<Expression<Boolean>> expressions = predicate.getExpressions();
Path<Object> firtsName = personRoot.get("author").get("information").get("firstName");
expressions.add(builder.equal(firtsName, "Marc"));
criteria.where( predicate );
criteria.select(personRoot);
List<Book> books = em.createQuery( criteria ).getResultList();
Criteria JPA Hibernate
List<Book> books = (List<Book>)sess.createCriteria(Book.class).add( Restrictions.eq("author.information.firstName", "Marc") ).list();
We recommend using hibernate criterias for convenience and possibilities.
Regards,
I have a JPA entity with a list of child entities. In this case a user entity with roles attached to it.
It looks (a bit simplified - some fields/methods omitted) like this:
#Entity
public class MyUser{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long myUserId;
private String username;
#OneToMany
#JoinTable(name = "userrole",
joinColumns = {
#JoinColumn(name="myUserId", unique = true)
},
inverseJoinColumns = {
#JoinColumn(name="roleId")
}
)
private Collection<Role> roles;
public Collection<Role> getRoles() {
return roles;
}
}
If intressting, the Role entity is very simple.
#Entity
public class Role {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long roleId;
private String role; // a few more string fields here .
When I add two users and a few hundred roles per user I get a wierd behaviour when I list the users. Each user get's listed a few hundred times (same user = same unique id).
The problematic code:
Query q = em.createQuery("SELECT u FROM MyUser u LEFT JOIN FETCH u.roles");
Collection<MyUser> users = q.getResultList();
for(MyUser u : users){
// print/use u here
}
However, when I just access the database and do select statements, it seems fine. Every user exists only once.
I use OpenJPA 1.2 together with a IBM DB2 database in this case.
I think you have your model wrong, typically a user-role relationship is not OneToMany but "ManyToMany" so you should change your code to look something like this:
#Entity
public class MyUser{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long myUserId;
private String username;
#ManyToMany //This should be many to many
#JoinTable(name = "userrole",
joinColumns = {
#JoinColumn(name="myUserId") //The userId in the join table should
//NOT be unique because the userId can
//be many times with different roles
},
inverseJoinColumns = {
#JoinColumn(name="roleId")
}
)
private Collection<Role> roles;
public Collection<Role> getRoles() {
return roles;
}
}
Try this way and see if it works.
Also your query shouldn't need the Left Join, the roles should be fetched automatically by JPA once you use the getRoles() method on each entity (using LAZY Fetch)
Actually, it's reasonable to have #ManyToMany mapping for User and UserRole entities. The problem with your query is that it returns all the rows from the join table what I believe you don't need. So just add group by u to your query as follows:
SELECT u FROM MyUser u LEFT JOIN FETCH u.roles GROUP BY u
and you'll be done.