It is possible to save same parent to 2 children:
I want to disable this possibility.
the domains:
#Entity
public class Child {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
Long id;
#OneToOne
Parent parent;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public Parent getParent() {
return parent;
}
public void setParent(Parent parent) {
this.parent = parent;
}
}
#Entity
public class Parent {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
Long id;
#OneToOne(mappedBy="parent")
private Child child;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
#PreRemove
private void preRemove() {
child.setParent(null);
}
}
How to change this code to disable possiblity of having same parent for 2 children? Should I craete FK or somethin? How do that in elegant way with JPA?
Define a #JoinColumn on your #OneToOne and add unique = true. This way uniqness of parents will be checked at the database side:
#OneToOne
#JoinColumn(name="PARENT_ID", unique = true)
Parent parent;
Related
Project is based on JPA persistance with two Entities (Deaprtment and Employee)
Department(OneToMany) and Employee(ManyToOne)
Whenever I send a request via API there's a StackOverFlow error. So far I back Traced the main cause which is the stack is full is indefinite recursion. Could someone explain why this happened ususally it shouldn't have confused by bidirectioanl relationship of entities.
package com.springjpacrud01.model;
import javax.persistence.*;
import java.util.List;
#Entity
#Table(name = "department")
public class Department {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
#Column(name = "name")
private String name;
#OneToMany(mappedBy = "department", fetch = FetchType.LAZY)
List<Employee> employees;
public Department() { }
public Department(Long id, String name) {
this.id = id;
this.name = name;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Employee> getEmployees() {
return employees;
}
public void setEmployees(List<Employee> employees) {
this.employees = employees;
}
}
import com.fasterxml.jackson.annotation.JsonBackReference;
import javax.persistence.*;
#Entity
#Table(name = "employees")
public class Employee {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(name = "name")
private String name;
#Column(name = "position")
private String position;
#ManyToOne
#JoinColumn(name = "department_id")
private Department department;
public Employee(Long id, String name, String position) {
this.id = id;
this.name = name;
this.position = position;
}
public Employee() {
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPosition() {
return position;
}
public void setPosition(String position) {
this.position = position;
}
public Department getDepartment() {
return department;
}
public void setDepartment(Department department) {
this.department = department;
}
}
After I just deleted the getters/setters from the Department entity it worked but
it shouldn't have work like that and I want why I cannot do relation pointing to each other entities? It couldn't form JSON response because of the infinite recursion of pointing to each other I guess. How can I solve it effectively in order to retrieve Employees by department ID, thank you)
If someone needs it I've solved this by understanding the deep root of the cause which was #JoinColumn created and addressed by Hibernate to that empty common column which I deleted manually. And when I was requesting the department_id of the employee via the employee repository Hibernate sort of got stuck in an infinite loop of going to the employee repository and from there to the department repository and in the department repository going to the employee repository. To stop that I've mapped the relation differently by making a configuration of the department
#OneToMany(mappedBy = "department", cascade= CascadeType.ALL, orphanRemoval=true) private Set<Employee> employeeHashSet = new HashSet<>();
And
#ManyToOne
#JoinColumn(name = "department_id")
private Department department;
Need make a relationship between same table. Example: the object "category" have subcategories and the subcategorie have other subcategorie.
In MySQL make a column and point to primary key of same table, but, howto make in JPA?
My code is:
#Entity
#Table(name = "objects")
public class JObject {
private long id;
private String name;
private JObject parentJObject;
private Set<JObject> jObjects;
public JObject(){
}
public JObject(long id){
this.id = id;
}
public JObject(String name){
this.name = name;
}
public JObject(String name, JObject parentJObject){
this.name = name;
this.parentJObject = parentJObject;
}
#Null
#JoinColumn(name="parent_object_id", referencedColumnName="id")
#ManyToOne(cascade=CascadeType.ALL)
public JObject getParentJObject() {
return parentJObject;
}
public void setParentJObject(JObject parentJObject) {
this.parentJObject = parentJObject;
}
#Null
#OneToMany(mappedBy = "parentJObject", cascade = CascadeType.ALL)
public Set<JObject> getJObjects() {
return jObjects;
}
public void setJObjects(Set<JObject> jObjects) {
this.jObjects = jObjects;
}
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
#NotNull
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
And the making objects:
JObject jObjectcategories = new JObject("Demo 1");
Set categoriesJObjects = new HashSet<JObject>(){{
add(new JObject("Demo 1.1", jObjectcategories));
}};
jObjectcategories.setJObjects(categoriesJObjects);
jObjectDao.save(new HashSet<JObject>() {{
add(jObjectcategories);
}});
But does not works. The log says:
List of constraint violations:[ ConstraintViolationImpl{interpolatedMessage='It has to be null', propertyPath=JObjects, rootBeanClass=class a.b.c.models.JObject, messageTemplate='{javax.validation.constraints.Null.message}'} ]
You need to be consistent in where you place your JPA annotations: either all on fields, or all on getters. But not mixed as you're doing.
The OneToOne should be a ManyToOne according to your description, since several objects share the same parent.
And the cascade ALL doesn't make sense: you don't want to delete a parent when a child is deleted.
I am trying to establish unidirectional relationship between two entities called Person and Address,while saving Person(containing collection of Address) getting org.hibernate.TransientObjectException: object references an unsaved transient instance.
When I change cascadeType=all,child objects are getting propagated.But the problem here is with cascadeType=all Hibernate also tries to delete child entities on Deleting Owning entity.I don't want that to happen because in ManyToMany relationship child entity might be being referenced by some other entity.Ideally cascadeType=persist should do the job but unfortunately that give me mentioned exception.
Can somebody help me out how can I save the child objects (Address) with cascadeType=persist.I just wonder why cascadeType=persist is not doing the task of persisting.
public class Person {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
private String name;
#LazyCollection(LazyCollectionOption.FALSE)
#ManyToMany(cascade={CascadeType.PERSIST,CascadeType.MERGE})
private Collection<Address> address=new HashSet<Address>();
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Collection<Address> getAddress() {
return address;
}
public void setAddress(Collection<Address> address) {
this.address = address;
}
}
#Entity(name="Address")
public class Address {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
#Column(name="id")
private Long id;
#Column(name="country")
private String country;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
}
In case of many- many relationship you always have to make use of JOIN Table(which is a third table).In that case you dont have a problem of Child entities getting deleted on deleting the Owning entity even if you use CASCADE-ALL.
Please see following post below:
Modeling many-to-many Relationship in JPA/Hibernate
I have one exception, which yold what I have no mapping on table. But I have this
Exeption is : \
AnnotationException: mappedBy reference an unknown target entity property: Relative.people in Person.relations
Relative entity is here:
#Entity
#Table(name = "relation")
public class Relative extends AbstractModel<UUID> implements Model<UUID> {
private UUID id;
private Person person;
private RelationTypeEnum relation;
public Relative() {
}
#Override
public void assignId() {
id = UUID.randomUUID();
}
#Override
#Id
#Column(name = "id")
public UUID getId() {
return id;
}
#ManyToOne
#JoinColumn(name="person_id", nullable=false)
public Person getPerson() {
return person;
}
#Column(name = "relation")
public RelationTypeEnum getRelation() {
return relation;
}
public void setId(UUID id) {
this.id = id;
}
public void setPerson(Person person) {
this.person = person;
}
public void setRelation(RelationTypeEnum relation) {
this.relation = relation;
}
}
And Person entity is here:
#Entity
#Table(name = "people")
public class Person extends AbstractModel<UUID> implements Model<UUID> {
private UUID id;
private String name;
private List<Relative> relations;
#Override
public void assignId() {
id = UUID.randomUUID();
}
#Override
#Id
#Column(name = "id")
public UUID getId() {
return id;
}
#Column(name = "name")
public String getName() {
return name;
}
#OneToMany(targetEntity=Relative.class, cascade=CascadeType.ALL,
mappedBy="people")
public List<Relative> getRelations() {
return relations;
}
public void setId(UUID id) {
this.id = id;
}
public void setName(String username) {
this.name = username;
}
public void setRelations(List<Relative> relations) {
this.relations = relations;
}
}
Solved.
Just changed
#Table(name = "people")
to
#Table(name = "person")
In my case there was a project which included a copy of the jar causing this issue. It was a web project which is including the jar inside its lib i.e. 2 copies of the same jar one with a different class version. Only discovered this when I physically opened the main ear and found the 2nd jar inside a web project.
My domain has a Category entity which has a biderectional relationship on itself. Each category can have a parent and children.
#Entity
public class Category implements DomainObject {
private Long id;
private Integer version;
private String name;
private Category parent;
private Set<Category> children;
#Override
#Id
#GeneratedValue
public final Long getId() {
return id;
}
#Version
public Integer getVersion() {
return version;
}
public void setVersion(Integer version) {
this.version = version;
}
public void setId(Long id) {
this.id = id;
}
#Column(unique=true, nullable=false)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
#ManyToOne
public Category getParent() {
return parent;
}
public void setParent(Category parent) {
this.parent = parent;
}
#OneToMany
#JoinColumn(name = "parent_id")
public Set<Category> getChildren() {
return children;
}
public void setChildren(Set<Category> children) {
this.children = children;
}
}
I have created the following query to fetch the "root" categories with their direct (level 1) children.
select distinct c from Category c left join fetch c.children where c.parent is null order by c.name
This actually works. My question is: why do I need the "JoinColumn" annotation on getChildren() to make this work and why can't I just make a "foin fetch" query, without "distinct"? If I remove "distinct" I get a multiplication. For each child of a parent, the entire parent is copied in the result set.
Is there a better way to do this? It just feels... a bit crappy.
In JPA you need to set distinct when you join a OneToMany, otherwise it will return duplicates.
This is required.
The JPA spec requires this, but it is an odd default, but relates to what happens in database joins.