Say I have a unidirectional #ManyToOne relationship like the following:
#Entity
public class Parent implements Serializable {
#Id
#GeneratedValue
private long id;
}
#Entity
public class Child implements Serializable {
#Id
#GeneratedValue
private long id;
#ManyToOne
#JoinColumn
private Parent parent;
}
If I have a parent P and children C1...Cn referencing back to P, is there a clean and pretty way in JPA to automatically remove the children C1...Cn when P is removed (i.e. entityManager.remove(P))?
What I'm looking for is a functionality similar to ON DELETE CASCADE in SQL.
If you are using hibernate as your JPA provider you can use the annotation #OnDelete. This annotation will add to the relation the trigger ON DELETE CASCADE, which delegates the deletion of the children to the database.
Example:
public class Parent {
#Id
private long id;
}
public class Child {
#Id
private long id;
#ManyToOne
#OnDelete(action = OnDeleteAction.CASCADE)
private Parent parent;
}
With this solution a unidirectional relationship from the child to the parent is enough to automatically remove all children. This solution does not need any listeners etc. Also a JPQL query like DELETE FROM Parent WHERE id = 1 will remove the children.
Relationships in JPA are always unidirectional, unless you associate the parent with the child in both directions. Cascading REMOVE operations from the parent to the child will require a relation from the parent to the child (not just the opposite).
You'll therefore need to do this:
Either, change the unidirectional #ManyToOne relationship to a bi-directional #ManyToOne, or a unidirectional #OneToMany. You can then cascade REMOVE operations so that EntityManager.remove will remove the parent and the children. You can also specify orphanRemoval as true, to delete any orphaned children when the child entity in the parent collection is set to null, i.e. remove the child when it is not present in any parent's collection.
Or, specify the foreign key constraint in the child table as ON DELETE CASCADE. You'll need to invoke EntityManager.clear() after calling EntityManager.remove(parent) as the persistence context needs to be refreshed - the child entities are not supposed to exist in the persistence context after they've been deleted in the database.
Create a bi-directional relationship, like this:
#Entity
public class Parent implements Serializable {
#Id
#GeneratedValue
private long id;
#OneToMany(mappedBy = "parent", cascade = CascadeType.REMOVE)
private Set<Child> children;
}
I have seen in unidirectional #ManytoOne, delete don't work as expected.
When parent is deleted, ideally child should also be deleted, but only parent is deleted and child is NOT deleted and is left as orphan
Technology used are Spring Boot/Spring Data JPA/Hibernate
Sprint Boot : 2.1.2.RELEASE
Spring Data JPA/Hibernate is used to delete row .eg
parentRepository.delete(parent)
ParentRepository extends standard CRUD repository as shown below
ParentRepository extends CrudRepository<T, ID>
Following are my entity class
#Entity(name = “child”)
public class Child {
#Id
#GeneratedValue
private long id;
#ManyToOne( fetch = FetchType.LAZY, optional = false)
#JoinColumn(name = “parent_id", nullable = false)
#OnDelete(action = OnDeleteAction.CASCADE)
private Parent parent;
}
#Entity(name = “parent”)
public class Parent {
#Id
#GeneratedValue
private long id;
#Column(nullable = false, length = 50)
private String firstName;
}
Use this way to delete only one side
#ManyToOne(cascade=CascadeType.PERSIST, fetch = FetchType.LAZY)
// #JoinColumn(name = "qid")
#JoinColumn(name = "qid", referencedColumnName = "qid", foreignKey = #ForeignKey(name = "qid"), nullable = false)
// #JsonIgnore
#JsonBackReference
private QueueGroup queueGroup;
#Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
Given annotation worked for me. Can have a try
For Example :-
public class Parent{
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
#Column(name="cct_id")
private Integer cct_id;
#OneToMany(cascade=CascadeType.REMOVE, fetch=FetchType.EAGER,mappedBy="clinicalCareTeam", orphanRemoval=true)
#Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
private List<Child> childs;
}
public class Child{
#ManyToOne(fetch=FetchType.EAGER)
#JoinColumn(name="cct_id")
private Parent parent;
}
You don't need to use bi-directional association instead of your code, you have just to add CascaType.Remove as a property to ManyToOne annotation, then use #OnDelete(action = OnDeleteAction.CASCADE), it's works fine for me.
Related
I am new to JPA. I have parent and several children. I am able to successfully save parent and associated child with Column Mapping using below code.
#Data
#Entity
#Table(name = "Parent")
public class Parent{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "ParentKey", nullable = false, length = 20)
private Long parentKey;
#Column(name = "ParentID", nullable = true, length = 60)
private String parentID;
#OneToMany(cascade = CascadeType.ALL)
#JoinColumn(name = "ParentKey", nullable = false)
private Set<Child> childSet = new HashSet<>(0);
}
#Data
#Entity
#Table(name = "Child")
public class Child {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long childKey;
private String ChildID;
}
I have a scenario where I receive only child records with parent ID. I lookup parent and want to use same child object and repository for saving additional child records. Since there is no reference for parent key, how can I achieve without duplicating child object.
Child Object does not have ParentKey. I do not want to make any changes to Parent when I am loading child records only.
I am using mySQL.
Thanks
First, you need a way to query DB that will get you Parent entity by parentID. If you are using spring data jpa module, you can add the following method to a ParentRepository
Optional<Parent> findByParentID(String parentID);
Assuming your service method looks like this, you first retrieve Parent from DB using parentID and then you can add children to that parent.
public void saveChildren(String parentID, Set<Child> children) {
Parent parent = parentRepository.findByParentID(parentID)
.orElseThrow(() -> <Your excp that says parent not found by parentID>);
// assuming you have filtered out duplicates, now you can save remaining as
parent.getChildSet().addAll(children);
parentRepository.save(parent);
}
Let's say I have the following "parent" pojo...
#Entity
#Table(name = "parent")
public class Parent{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#OneToMany(fetch=FetchType.LAZY, mappedBy = "parent", cascade = {CascadeType.ALL})
#JsonIgnoreProperties("parent")
List<Child> children;
}
and I have the following child POJO :
#Entity
#Table(name = "child")
public class Child{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#ManyToOne
#JoinColumn(name="parent_id")
private Parent parent;
}
The result of this will be that I have two tables, and my jpa repository will perform queries using the parent_id field within the child table.
However, What if I want it be like a lookup, where by there is a third table for the relationship, where I have the child id and the parent id as a row, and that would be the relationship? can I modify my spring - jpa / hibernate setup for that? If so, some help would be appreciated!
I have a many-to-one bidirectionnal relationship between a parent and child entity. The problem is, when i'm persisting the child, the parent_id isn't persisted. The other fields are fine, but parent_id stay at NULL. I'm using Spring Data JPA with Hibernate and mapstruct to convert between entity and dto, if that can help.
The java files are the following :
#Entity
#Table(name = "Parent")
public class ParentEntity implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#OneToMany (fetch = FetchType.LAZY, mappedBy="parent_entity", cascade = { CascadeType.ALL })
private List<Child> children;
}
#Entity
#Table(name = "Child")
public class ChildEntity implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#ManyToOne(optional = true)
#JoinColumn(nullable = true, name = "parent_entity_id", insertable = false, updatable = false)
private Parent parent_entity;
}
I already tried a bunch of answers from SO, but to no avail for now.
Since you're using bidirectional relationship, you are now responsible to set a parent for your child. And remove insertable = false.
As far as I know. You have to add each other in both parent and child. Only adding children to the list does not seem to work.
Try it out, and see if that fixes the problem.
Right now, if I want to delete a Parent entry from database, I would use cascade annotation in the Parent class, so that a deletion of Parent would also delete any children tied to it. Like this:
#Entity
public class Parent implements Serializable {
#Id
#GeneratedValue
private long id;
#OneToMany(mappedBy = "parent", cascade = CascadeType.REMOVE)
private Set<Child> children;
}
#Entity
public class Child implements Serializable {
#Id
#GeneratedValue
private long id;
#ManyToOne
#JoinColumn
private Parent parent;
}
The actual deletion would be like this:
this.parentRepository.delete(parentID);
However, if I want to explicitly choose whether to cascade delete or to simple delete, how would I do that?
I don't think I can choose to turn off the cascade annotation in code manually, so is there a way to cascade delete without using annotation?
You should not delete parent if child has relation on parent. It's not good way. In db child should not have notNull restriction on parent
But you really want control cascade deletion, I would recommend use #EntityListeners:
#EntityListeners({ParentJpaCallbacksListener.class})
#Entity
public class Parent implements Serializable {
#Id
#GeneratedValue
private long id;
#OneToMany(mappedBy = "parent")
private Set<Child> children;
}
where
#Component
public class ParentJpaCallbacksListener {
#Autoware ChildRepository childRepository;
#PreRemove
// or #PostRemove
void preRemove(Parent parent) {
// your cascade deletion logic
// for example use childRepository to delete some children
}
}
In this way you should not have cascade = CascadeType.REMOVE.
I have Hibernate Entities that look something like this (getters and setters left out):
#Entity
public class EntityA {
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "parent_id")
private EntityB parent;
}
#Entity
public class EntityB extends SuperEntity {
#OneToMany(mappedBy = "parent")
#Fetch(FetchMode.SUBSELECT)
#JoinColumn(name = "parent_id")
private Set<EntityA> children;
}
#MappedSuperclass
public class SuperEntity {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id")
private long itemId;
}
When I query for EntityA it loads fine, with the parent association being replaced by a Hibernate proxy (as it is Lazy). If I want access to the parent's id I perform the following call:
EntityA entityA = queryForEntityA();
long parentId = entityA.getParent().getItemId();
As I understand that call should NOT make a roundtrip to the database, as the Id is stored in the EntityA table, and the proxy should only return that value. However, in my case this generates a SQL statement which fetches EntityB and only then returns the Id.
How can I investigate the problem? What are some likely causes of this incorrect behaviour?
As I understand that call should NOT make a roundtrip to the database, as the Id is stored in the EntityA table, and the proxy should only return that value.
Use property access type. The behavior you're experiencing is a "limitation" of field access type. Here is how Emmanuel Bernard explained it:
That is unfortunate but expected. That's one of the limitations of field level access.
Basically we have no way to know that getId() indeed only go and access the id field. So we need to load the entire object to be safe.
So change your code into:
#Entity
public class EntityA {
private EntityB parent;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "parent_id")
public EntityB getParent() {
return parent;
}
...
}
#MappedSuperclass
public class SuperEntity {
private long itemId;
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id")
public long getItemId() {
return itemId;
}
...
}
Related question
Hibernate Annotations - Which is better, field or property access?
References
Proxy loaded on getId-call when using annotations on fields
proxy getId => why sql is generated !
HHH-3718 (if this issue can ever be solved)
What you say makes sense - that it would not make a DB hit since EntityA contains the parent ID. I am just not sure if the getParent() call actually loads the EntityB object regardless of whether all you're interested in is the ID. You might try marking the children collection (and any other fields) as Lazy if you want to save the DB hit.
#Entity
public class EntityB : SuperEntity {
#OneToMany(mappedBy = "parent", fetch = FetchType.LAZY)
#Fetch(FetchMode.SUBSELECT)
#JoinColumn(name = "parent_id")
private Set<EntityA> children;
}
As for Hibernate:
This behavior has been changed since Hibernate 5.2.12.