My project is using JPA 2 with Hibernate and there is a single table inheritance setup for dealing with two types of customer. When I try to query data on customers by using Spring Data JPA Specification, I always get incorrect result. I think it's because I create the query wrong and still got no idea how to make it right.
Here is my test code (I am trying search customer by company name):
#Test
public void test() {
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Customer> customerQuery = criteriaBuilder.createQuery(Customer.class);
Root<Customer> customerRoot = customerQuery.from(Customer.class);
Root<CompanyCustomer> companyCustomerRoot = customerQuery.from(CompanyCustomer.class);
CriteriaQuery<Customer> select = customerQuery.select(customerRoot);
select.where(criteriaBuilder.equal(companyCustomerRoot.get(CompanyCustomer_.companyName), "My Company Name"));
TypedQuery<Customer> query = entityManager.createQuery(select);
List<Customer> results = query.getResultList();
assertEquals(1, results.size()); // always got size 2
}
SQL script in the log:
Hibernate:
select
customer0_.id as id2_16_,
customer0_.type as type1_16_,
customer0_.first_name as first_na8_16_,
customer0_.last_name as last_nam9_16_,
customer0_.company_name as company13_16_
from
customers customer0_ cross
join
customers companycus1_
where
companycus1_.type='COMPANY'
and companycus1_.company_name=?
There are two records in my database:
insert into customers (id, type, company_name) values (1, 'COMPANY', 'My Company Name');
insert into customers (id, type, first_name, last_name) values (2, 'PERSONAL', 'My First Name', 'My Last Name');
My single table inheritance setup:
#Entity
#Table(name = "customers")
#DiscriminatorColumn(name = "type", discriminatorType = DiscriminatorType.STRING)
public abstract class Customer {
#Enumerated(EnumType.STRING)
#Column(name = "type", insertable = false, updatable = false)
private CustomerType type;
private String contactNumber;
}
#Entity
#DiscriminatorValue("PERSONAL")
public class PersonalCustomer extends Customer {
private String firstName;
private String lastName;
}
#Entity
#DiscriminatorValue("COMPANY")
public class CompanyCustomer extends Customer {
private String companyName;
}
public enum CustomerType {
COMPANY, PERSONAL;
}
I found the answer from
JPA Criteria Query over an entity hierarchy using single table inheritance
Solution:
Use CriteriaBuilder.treat() to downcast Customer entity instead of using CriteriaQuery.from()
Related
I am trying to write simple Pet-project, I use Hibernate in DAO layer. I have entity Group with field Students.
#Data
#AllArgsConstructor
#RequiredArgsConstructor
#EqualsAndHashCode
#ToString
#Builder
#Entity
#Table(name = "groups")
#NamedQueries({
#NamedQuery(name = "get all groups", query = "from Group"),
#NamedQuery(name = "find group by id", query = "select g from Group g join fetch g.students where g.id=:groupId"),
#NamedQuery(name = "find group by name", query = "from Group g where g.name like :groupName"),
#NamedQuery(name = "find number of groups", query = "select count(*) from Group"),
#NamedQuery(name = "find group and sort by name", query = "from Group order by name, id"),
#NamedQuery(name = "find group and sort by id", query = "from Group order by id")
})
public class Group {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column
private int id;
#Column
private String name;
#OneToMany(cascade={CascadeType.PERSIST, CascadeType.DETACH, CascadeType.MERGE, CascadeType.REFRESH})
#JoinTable(
name="studentsGroups",
joinColumns=#JoinColumn(name="groupId"),
inverseJoinColumns=#JoinColumn(name="studentId")
)
#LazyCollection(LazyCollectionOption.FALSE)
private List<Student> students;
}
in DAO layer for exaple I have method
#Transactional
public Optional<Group> findById(int groupId) {
Session session = sessionFactory.getCurrentSession();
return Optional.ofNullable(session.get(Group.class, groupId));
}
I want to check my DAO and I am writing junit test. I use assertThat to compare entity from database and entity from test data. In test data, field students have type ArrayList but from Hibernate get type PersistentBag and I can't compare these fields although all data are same.
#Test
public void givenFindGroupById_whenFindGroupById_thenGroupWasFound() {
Optional<Group> actual = groupDao.findById(2);
assertThat(actual).isPresent().get().isEqualTo(expectedGroups.get(1));
}
List<Group> expectedGroups = Arrays.asList(
Group.builder().id(1).name("a2a2").students(expectedStudentsForGroupA2A2Name).build(),
Group.builder().id(2).name("b2b2").students(expectedStudentsForGroupB2B2Name).build(),
Group.builder().id(3).name("c2c2").students(expectedStudentsForGroupC2C2Name).build(),
Group.builder().id(4).name("d2d2").students(expectedStudentsForGroupD2D2Name).build());
Is there some way to convert PersistentBag to ArrayList, or I am doing something wrong?
PersistentBag uses Object's equals method for equals() and hashCode() Bug.
FIX:
Exclude students field for equals check by adding #EqualsAndHashCode.Exclude over it.
Now assert the Students values: assertThat(actual.get().getStudents()).containsOnlyElementsOf(expectedGroups.get(1).getStudents())
Model:
#Entity
public class User {
#Id
private Integer id;
#JoinColumn(name = "user_id")
#OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true)
private List<Project> projects;
}
#Entity
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
#DiscriminatorColumn(name = "Type")
public abstract class Project {
#Id
private Integer id;
private String name;
}
#Entity
#DiscriminatorValue("Administrative")
public class AdminProject extends Project {
private String departmentName;
}
#Entity
#DiscriminatorValue("Design")
public class DesignProject extends Project {
private String companyName;
}
I am trying to use JPA's criteria api to query for User entities based on an attribute of an implementation of Project. For example, query all users that have a project with "SOME_NAME" department (that field does not exist on DesignProject).
I see there is a way of doing so via downcasting of the Project entity for the query. I am trying something similar to:
CriteriaBuilder cb...
Root<User> userRoot...
root = ((From) root).join("projects", JoinType.LEFT);
root = cb.treat(root, AdminProject.class);
root = root.get("departmentName");
Exception:
org.springframework.dao.InvalidDataAccessApiUsageException: org.hibernate.hql.internal.ast.QuerySyntaxException: Invalid path: 'generatedAlias2.departmentName' [select generatedAlias0 from io.github.perplexhub.rsql.model.User as generatedAlias0 left join generatedAlias0.projects as generatedAlias1 where treat(generatedAlias2 as io.github.perplexhub.rsql.model.AdminProject).departmentName=:param0]; nested exception is java.lang.IllegalArgumentException: org.hibernate.hql.internal.ast.QuerySyntaxException: Invalid path: 'generatedAlias2.departmentName' [select generatedAlias0 from io.github.perplexhub.rsql.model.User as generatedAlias0 left join generatedAlias0.projects as generatedAlias1 where treat(generatedAlias2 as io.github.perplexhub.rsql.model.AdminProject).departmentName=:param0]
What am I missing? Is it something related to the join, or how the downcasting occurs afterwards?
Edit
After the answer by #K.Nicholas, I have managed to make the query work on an isolated scenario, but not on my app.
But, I noticed that the entityManager.createQuery(query) call throws the exception above when called for the first time, and it works if I call it again without changing the query object. Here is the query generated on the second call (this query finds the objects I want from the database):
select generatedAlias0 from User as generatedAlias0 left join generatedAlias0.projects as generatedAlias2 where treat(generatedAlias2 as io.github.perplexhub.rsql.model.AdminProject).departmentName=:param0
Why is the entity manager creating two different queries when called two consecutive times?
I would do the Entitys a little different, as you will see. The main concern is that you are using User as your root with a join to a list of Projects. This is a concern because you should have the foreign key on the Project class and use the projects field as a query only field. That is what I have done. It works better that way. It is also a concern because you have to do a join fetch instead of a join so that the projects get fetched along with the users.
So, first, the entities are like so:
#Entity
public class User {
#Id
private Integer id;
#OneToMany(mappedBy="user")
private List<Project> projects;
}
#Entity
#Inheritance(strategy = InheritanceType.SINGLE_TABLE)
#DiscriminatorColumn(name = "Type")
public abstract class Project {
#Id
private Integer id;
private String name;
#ManyToOne
private User user;
}
#Entity
#DiscriminatorValue("Administrative")
public class AdminProject extends Project {
private String departmentName;
}
#Entity
#DiscriminatorValue("Design")
public class DesignProject extends Project {
private String companyName;
}
After a bit a digging I found a JPQL query that does the trick. This was a starting point:
List<User> users = entityManager.createQuery("select distinct(u) from User u join fetch u.projects p where TYPE(p) = 'Administrative' and p.departmentName = 'dept1'", User.class).getResultList();
After a bit more digging I found that the treat worked fine if you do it correctly and that with JPA 2.1 you should use an EntityGraph do get the join to do a fetch.
CriteriaBuilder builder = entityManager.getCriteriaBuilder();
CriteriaQuery<User> query = builder.createQuery(User.class);
Root<User> root = query.from(User.class);
Join<User, Project> join = root.join("projects");
query.select(root).where(builder.equal(builder.treat(join, AdminProject.class).get("departmentName"), "dept1"));
EntityGraph<User> fetchGraph = entityManager.createEntityGraph(User.class);
fetchGraph.addSubgraph("projects");
users = entityManager.createQuery(query.distinct(true)).setHint("javax.persistence.loadgraph", fetchGraph).getResultList();
As a side note the queries generated as slightly different but I didn't look that closely at them. You should.
I have an entity as below. I am curious if it is possible to create a relationship as I will be describing with the example:
I am creating 2 Person entities Michael and Julia.
I am adding Julia to Michael's friends set.
After that I am retrieving Michael as a JSON response and Julia is available in the response. But when I am retrieving Julia, her friends set is empty. I want to create the bidirectional friendship relation by saving just one side of the friendship. I would like to get Michael on Julia's friends set without doing any other operations. I think that it must be managed by Hibernate. Is it possible and how should I do it?
#ToString(exclude = "friends") // EDIT: these 2 exclusion necessary
#EqualsAndHashCode(exclude = "friends")
public class Person{
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id")
private Long id;
#Column(name = "name",unique = true)
private String name;
#JsonIgnoreProperties("friends") // EDIT: will prevent the infinite recursion
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(name = "FRIENDSHIP",
joinColumns = #JoinColumn(name = "person_id",
referencedColumnName = "id"),
inverseJoinColumns = #JoinColumn(name = "friend_id",
referencedColumnName = "id"))
private Set<Person> friends;
Here is my service layer code for creating a friendship:
#Override
public Person addFriend(String personName, String friendName)
throws FriendshipExistsException, PersonNotFoundException {
Person person = retrieveWithName(personName);
Person friend = retrieveWithName(friendName);
if(!person.getFriends().contains(friend)){
person.getFriends().add(friend);
return repository.save(person);
}
else{
throw new FriendshipExistsException(personName, friendName);
}
}
Related Question:
N+1 query on bidirectional many to many for same entity type
Updated the source code and this version is working properly.
// Creating a graph to help hibernate to create a query with outer join.
#NamedEntityGraph(name="graph.Person.friends",
attributeNodes = #NamedAttributeNode(value = "friends"))
class Person {}
interface PersonRepository extends JpaRepository<Person, Long> {
// using the named graph, it will fetch all friends in same query
#Override
#EntityGraph(value="graph.Person.friends")
Person findOne(Long id);
}
#Override
public Person addFriend(String personName, String friendName)
throws FriendshipExistsException, PersonNotFoundException {
Person person = retrieveWithName(personName);
Person friend = retrieveWithName(friendName);
if(!person.getFriends().contains(friend)){
person.getFriends().add(friend);
friend.getFriends().add(person); // need to setup the relation
return repository.save(person); // only one save method is used, it saves friends with cascade
} else {
throw new FriendshipExistsException(personName, friendName);
}
}
If you check your hibernate logs, you will see:
Hibernate: insert into person (name, id) values (?, ?)
Hibernate: insert into person (name, id) values (?, ?)
Hibernate: insert into friendship (person_id, friend_id) values (?, ?)
Hibernate: insert into friendship (person_id, friend_id) values (?, ?)
I have an Entity called Student
#Entity
#Table(name = "students")
public class Student implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "STUDENT_ID")
private Integer studentId;
#Column(name = "STUDENT_NAME", nullable = false, length = 100)
private String studentName;
#OneToMany(fetch = FetchType.EAGER, mappedBy = "student", cascade = CascadeType.ALL)
private List<Note> studentNotes;
// Some other instance variables that are not relevant to this question
/* Getters and Setters */
}
and an entity called as Note
#Entity
#Table(name = "notes")
public class Note implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "NOTE_ID")
private Integer noteId;
#Column(name = "NOTE_CONTENT")
private String noteText;
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name = "STUDENT_ID")
private Student student;
/* Getters and Setters */
}
As you can see the relationship dictates that a Student can have multiple number of notes.
For displaying some information about the student on a particular page I need only the studentName, count of notes and all the notes.
I created a StudentDTO for that and it looks something like this:
public class StudentDTO {
private Long count;
private String name;
private List<Note> notes;
/* Getters and setters */
}
And I am using the following code to map the Student and Notes returned from the DB to the StudentDTO
private static void testDTO() {
Session session = getSessionFactory().openSession();
String queryString = "SELECT count(n) as count, s.studentName as name, s.studentNotes as notes " +
"from Student s join s.studentNotes n where s.id = 3";
Query query = session.createQuery(queryString);
List<StudentDTO> list = query.setResultTransformer(Transformers.aliasToBean(StudentDTO.class)).list();
for (StudentDTO u : list) {
System.out.println(u.getName());
System.out.println(u.getCount());
System.out.println(u.getNotes().size());
}
}
The above code fails when there are notes fetched in the query but if I remove the notes and get only name and count it works fine.
When notes is included in the query, this is the error that is fired by Hibernate:
select
count(studentnot2_.NOTE_ID) as col_0_0_,
. as col_3_0_,
studentnot3_.NOTE_ID as NOTE_ID1_2_,
studentnot3_.NOTE_CONTENT as NOTE_CON2_2_,
studentnot3_.STUDENT_ID as STUDENT_3_2_
from
students studentx0_
inner join
notes studentnot2_
on studentx0_.STUDENT_ID=studentnot2_.STUDENT_ID
inner join
notes studentnot3_
on studentx0_.STUDENT_ID=studentnot3_.STUDENT_ID
where
studentx0_.STUDENT_ID=3;
And this is the error message that I get:
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'as col_3_0_, studentnot3_.NOTE_ID as NOTE_ID1_2_, studentnot3_.NOTE_CONTENT as N' at line 1
Now I can see where the query is wrong but it is generated by Hibernate, not something that I have control on. Is there something that I need to change in my queryString to acheive the result that I need.
I do not want to manually map the results to my DTO, is there a way that I can directly map my studentNotes in Student.java to notes in StudentDTO.java
Looks like this query is wrong. The better way is to get just the student. You can always get collection of notes from a student.
Session session = getSessionFactory().openSession();
String queryString = from Student s where s.studentId = 3;
Query query = session.createQuery(queryString);
Student student = query.getSingleResult();
sysout(student.getNotes().size())
Also, I never retrieved collection this way in SELECT clause; so, not sure but do you really need
join s.studentNotes
in your query? Not sure if my answer is helpful.
Your query is wrong as you would need two joins to also select the count of notes, but that's not even necessary, as you could determine the count by just using the size of the notes collection.
I created Blaze-Persistence Entity Views for exactly that use case. You essentially define DTOs for JPA entities as interfaces and apply them on a query. It supports mapping nested DTOs, collection etc., essentially everything you'd expect and on top of that, it will improve your query performance as it will generate queries fetching just the data that you actually require for the DTOs.
The entity views for your example could look like this
#EntityView(Student.class)
interface StudentDTO {
#Mapping("studentName")
String getName();
#Mapping("studentNotes")
List<NoteDTO> getNotes();
default int getCount() { return getNotes().size(); }
}
#EntityView(Note.class)
interface NoteDTO {
// attributes of Note that you need
#IdMapping Integer getId();
String getNoteText();
}
Querying could look like this
StudentDTO student = entityViewManager.find(entityManager, StudentDTO.class, studentId);
I want to execute a query like this:
SELECT Table1.COL1,
Table1.COL2,
(SELECT SUM(Table2.COL3)
FROM Table2
WHERE Table2.UID = Table1.UID) SUMOF
FROM Table1;
How can I do it?
I usually create a Criteria add ProjectionList to it, to fill COL1 and COL2 only.
I have created a DetachedCriteria to calculate the sum...
Now, how to attach this detached criteria to the main one? My intuition says - it's some sort of Projection which needs to be added to the list, but I don't see how. Also, not sure how WHERE Table2.COL4 = Table1.COL5 of detached criteria will work.
Also, I'm sure this query might be written in different way, for example with join statement. It's still interesting if there's a way to run it like this.
DetachedCriteria and main Criteria
DetachedCriteria detachedCriteria = DetachedCriteria.forClass(Table2.class, "table2");
detachedCriteria
.setProjection(
Projections.projectionList()
.add(Projections.sum("table2.col3"), "sumCol3")
)
.add(Restrictions.eq("table2.uid", "table1.uid"))
;
Criteria criteria = session.createCriteria(Table1.class, "Table1");
criteria
.setProjection(
Projections.projectionList()
.add(Projections.property("Table1.col1"), "col1")
.add(Projections.property("Table1.col2"), "col2")
)
;
Entities (very short version)
#Entity
#Table(name = "Table1")
public class Table1 {
#Id
#Column(name = "uid")
public String getUid();
#Column(name = "col1")
public String getCol1();
#Column(name = "col2")
public String getCol2();
#Column(name = "col3")
public String getCol3();
#Column(name = "col4")
public String getCol4();
#Column(name = "col5")
public String getCol5();
}
#Entity
#Table(name = "Table2")
public class Table2 {
#Id
#Column(name = "uid")
public String getUid();
#Column(name = "col3")
public BigDecimal getCol3();
#Column(name = "col4")
public String getCol4();
#Column(name = "col5")
public String getCol5();
}
For a correlated subquery (like the one you presented above), you can use #Formula which can take an arbitrary SQL query. Then, you'll need to fetch the entity and the subquery will be executed.
However, a native SQL is more elegant if you only need this query for a single business requirement.
As for derived table queries (e.g. select from select), neither JPA nor Hibernate support derived table queries for a very good reason.
Entity queries (JPQL pr Criteria) are meant to fetch entities that you plan to modify.
For a derived table projection, native SQL is the way to go. Otherwise, why do you think EntityManager offers a createNativeQuery method?