I'm a beginner to the JPA/JPQL stuff and I'm having problems fetching many-to-one relationships when I make the relationship bi-directional. Here is the JPQL:
select c from Child c join fetch c.parent
Here are the two simple classes:
#Entity
public class Parent {
#Id
private int id;
private String title;
#OneToMany(mappedBy = "parent")
private Set<Child> children;
}
#Entity
public class Child {
#Id
private int id;
#ManyToOne(fetch = FetchType.LAZY)
private Parent parent;
}
The equivalent SQL query executed by datanucleus is:
SELECT 'com.*.Child' AS NUCLEUS_TYPE,`C`.`ID`,`C`.`PARENT_ID` FROM `CHILD` `C` INNER JOIN `PARENT` `B0` ON `C`.`PARENT_ID` = `B0`.`ID`
Now if I completely remove the reference to "children" in Parent, the SQL is exactly what I need:
SELECT 'com.*.Child' AS NUCLEUS_TYPE,`C`.`ID`,`B0`.`ID`,`B0`.`TITLE` FROM `CHILD` `C` INNER JOIN `PARENT` `B0` ON `C`.`PARENT_ID` = `B0`.`ID`
To be clear: what I'm trying to achieve is to fetch the child's parent with my JPQL query.
Update: I just tried these two classes with EclipseLink and this works, so looks like this problem is Datanucleus-specific.
You need #JoinColumn to create bidirectional relation:
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "parent_id")
private Parent parent;
If you are using JPA annotations select c from Child c and than child.getParent() on objects from database should be enough.
You need to use #JoinColumn in the Child class and try this.
Parent:
#OneToMany(targetEntity = Child.class, fetch = FetchType.EAGER, mappedBy = "parent", cascade=CascadeType.ALL)
Child:
#ManyToOne(targetEntity=Parent.class, fetch = FetchType.EAGER, cascade=CascadeType.ALL)
#JoinColumn(name="id", nullable = false)
And when you fetch the data from parent table it will automatically contains the associated data from the child table in the Set 'children'
Nevermind, this was a Datanucleus bug. It has been fixed in datanucleus-rdbms-3.2.6. This is the commit for the fix:
http://sourceforge.net/p/datanucleus/code/18118/
Related
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.
I am a JPA newbie and trying to understand #JoinTable annotation for Bidirectional OneToMany relationship b/w Project and Task Entities where Project can have multiple tasks.
I can use #JoinTable with Entity having #ManyToOne annotation, but when I am placing #JoinColumn on the other Entity having #OneToMany, I am not getting an option to specify "mappedBy" attribute on #ManyToOne annotation.
I would like to know why ?
I have tried placing #JoinTable annotation on both the entities but then Hibernate is itrying to insert two records in Join table
Project Entity :-
#Entity
#Data
public class Project {
#Id
#Column(name = "project_pk")
#GeneratedValue
private Long id;
#Column(name = "project_name")
private String name;
#OneToMany(mappedBy = "project", cascade = CascadeType.ALL)
List<Task> tasks;
}
Tasks Entity :-
#Entity
#Data
public class Task {
#Id
#GeneratedValue
#Column(name = "task_pk")
private Long id;
public Task() {
}
private String name;
#ManyToOne(cascade = CascadeType.ALL)
#JoinTable(name = "project_related_tasks",
inverseJoinColumns = #JoinColumn(name = "project_id", referencedColumnName = "project_pk"),
joinColumns = #JoinColumn(name = "task_id", referencedColumnName = "task_pk")
)
private Project project;
public Task(String name) {
this.name = name;
}
}
There are two ways to implement one-to-many relations:
Using a join table
Using a foreign key on the many-to-one side
mappedBy is used for the second way (using a foreign key). You don't have to specify mappedBy, if you want to use a join table.
Using a join table is not very good idea because you can't control that join table using Hibernate. For example you can't just add a record to a join table directly.
what is #JoinColumn and how it is used in Hibernate
I have a unidirectional, one-to-many, parent/child relation.
In my test case, I have 1 parent with 2 children which are inserted via cascading insert.
Looking at the queries that are ran, I have 1 insert for the parent, 1 insert and two update queries for each of the children. The updates for the foreign key - they are setting the parent_id column in the child table, but I can see that the parent_id has already been set correctly by the insert.
Here is an example
#Entity
#Table(name = "PARENT")
public class Parent
{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "ID")
private Long parentId;
#OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinColumn(name = "parent_id", nullable=false)
private List<Child> children;
}
#Entity
#Table(name = "CHILD")
public class Child
{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "ID")
private Long id;
#Column(name = "PARENT_ID")
private Long parentId;
//some other field
}
//The test looks like this
Parent parent = new Parent();
Child child1 = new Child();
Child child2 = new Child();
//set all fields
parent.addChild(child1);
parent.addChild(child2);
em.merge(parent);
Is it possible to not have the update queries?
Is it possible to insert all children in a single query?
You might try persist instead of merge
JPA EntityManager: Why use persist() over merge()?
No. It is not possible. because after insert in parent table, a child table can be inserted.
First of all, sorry for my English.
So, I'm working with MS SQL Server with hibernate and i faced with a problem.
I have next mapping of one of the tables in my DB:
#Entity(name = " ... ")
public class Entity extends BaseEntity implements Comparable {
#Id
#Column(name = "...")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#Column(name = "parent_entity_id", insertable = false, updatable = false)
private Integer parentId;
#ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.PERSIST})
#JoinColumn(name = "parent_entity_id")
private Entity parent;
#OneToMany(mappedBy = "parent", fetch = FetchType.LAZY, cascade = {CascadeType.REMOVE}, orphanRemoval = true)
private Set<Entity> children;
//other fields, setters, getters
}
That means, that my Entity objects can have children, which are also an Entity objects.
So, my problems is that I can't correctly delete parent with all his children. When I try to remove parent, i get an SQL error:
The DELETE statement conflicted with the SAME TABLE REFERENCE
So, any ideas, how to solve this problem?
You have a foreign key defined between parent_entity_id and id. Set it to allow cascading deletes: deleting a parent will delete all it's children, and all their children et cetera.
Be sure you actually want this to happen!
I'm struggling with how to create the following relationship in JPA. It's a OneToOne Unidirectional relationship where the parent knows the child, but the child doesn't know the parent, but I want the child table to have the FK to the parent. I've tried different versions of mapped by and join column, but apparently whatever combination I come up with doesn't seem to work. And my googlefoo isn't helping me with an answer either. Here's what I have now.
#Entity
class Parent
{
#OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true, mappedBy = "child")
private Child child
}
#Entity
class Child
{
private bool someField
}
Is there a way to do this that I'm just missing?
If this
#OneToOne(..)
#JoinColumn(name = "parent_id")
private Child child;
does not work, try this:
#OneToOne(..)
#JoinColumn(table = "child", name = "parent_id")
private Child child;