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Cascade remove relation without cascade remove target

I have a ManyToMany-relation between student and teacher in a Student_Teacher-table (Entityless).
Student: Teacher(owning-side): Student_Teacher
1= Tim 50= Mrs. Foo 1= 1 50
2= Ann 51= Mr. Bar 2= 1 51
3= 2 50
4= 2 51
As you see above every Student is currently related to every Teacher.
Now I like to remove Ann and I like to use the database's cascading techique to remove entries from the Student_Teacher-table but I do neither like to remove other Students, nor Teacher, nor other relationship.
This is what I have in the Student-Entity:
#ManyToMany(mappedBy="students")
public Set<Teacher> getTeachers() {
return teachers;
}
This is what I have in the Teacher-Entity:
#ManyToMany
#JoinTable(name="Student_Teacher", joinColumns = {
#JoinColumn(name="StudentID", referencedColumnName = "TeacherID", nullable = false)
}, inverseJoinColumns = {
#JoinColumn(name="TeacherID", referencedColumnName = "StudentID", nullable = false)
})
public Set<Student> getStudents() {
return students;
}
Now I like to use the database's delete cascade functionality. I repeat: The database's delete cascade functionality targeting the Student_Teacher-table only!
The problem:
org.h2.jdbc.JdbcSQLException: Referentielle Integrität verletzt: "FK_43PMYXR2NU005M2VNEB99VX0X: PUBLIC.Student_Teacher FOREIGN KEY(StudentID) REFERENCES PUBLIC.Student(StudentID) (2)"
Referential integrity constraint violation: "FK_43PMYXR2NU005M2VNEB99VX0X: PUBLIC.Student_Teacher FOREIGN KEY(StudentID) REFERENCES PUBLIC.Student(StudentID) (2)"; SQL statement:
delete from "Student" where name='Ann'
at org.h2.message.DbException.getJdbcSQLException(DbException.java:345)
at org.h2.message.DbException.get(DbException.java:179)
at org.h2.message.DbException.get(DbException.java:155)
at org.h2.constraint.ConstraintReferential.checkRow(ConstraintReferential.java:425)
What i can not use is the
#ManyToMany(cascade={CascadeType.REMOVE})
Because of the documetation tells me:
(Optional) The operations that must be cascaded to the target of the association.
The "target" is the Teacher, so this cascade would remove the Teacher (what I do not like to remove).
Question:
How to configure the entitys to remove Ann and the relation only using the database's cascade functionality?
Proof of Concept:
I tried another feature, I have noticed the possibility to configure the foreign-key nativly like this:
#ManyToMany(cascade = { CascadeType.REMOVE })
#JoinTable(name="Student_Teacher", joinColumns = {
#JoinColumn(name="StudentID", referencedColumnName = "TeacherID", nullable = false, foreignKey=#ForeignKey(foreignKeyDefinition="FOREIGN KEY (StudentID) REFERENCES Student ON DELETE NO ACTION"))
}, inverseJoinColumns = {
#JoinColumn(name="TeacherID", referencedColumnName = "StudentID", nullable = false, foreignKey=#ForeignKey(foreignKeyDefinition="FOREIGN KEY (TeacherID) REFERENCES Teacher ON DELETE NO ACTION"))
})
public Set<Student> getStudents() {
return students;
}
The problem is: This works fine but to trigger the removal of the entries in Student_Teacher I have to specify #ManyToMany(cascade = { CascadeType.REMOVE }) on both sides. Hibernate do not parse the foreignKeyDefinition and only see the CascadeType.REMOVE and drops the target-entitys (and the referenced Student Tim) out of the cache, but they are still in the database!!! So I have to clear the hibernate-session immendentelly after drop to re-read the existence of the Teachers Mrs. Foo and Mr. Bar and the Student Tim.

Now I like to use the database's delete cascade functionality. I
repeat: The database's delete cascade functionality targeting the
Student_Teacher-table only!
Simply define the cascade deletion on the database schema level, and the database would do it automatically. However, if the owning side of the association is loaded/manipulated in the same persistence context instance, then the persistence context will obviously be in an inconsistent state resulting in issues when managing the owning side, as Hibernate can't know what is done behind its back. Things get even more complicated if second-level caching is enabled.
So you can do it and take care not to load Teachers in the same session, but I don't recommend this and I write this only as an answer to this part of the question.
How to configure the entities to remove Ann and the relation only
using the database's cascade functionality?
There is no such configuration on JPA/Hibernate level. Most DDL declarations in mappings are used only for automatic schema generation, and are ignored when it comes to entity instances lifecycle and association management.
What i can not use is the
#ManyToMany(cascade={CascadeType.REMOVE})
Cascading of entity lifecycle operations and association management are two different notions that are completely independent of each other. Here you considered the former while you need the latter.
The problem you're facing is that you want to break the association from the Student (inverse side marked with mappedBy) when the Teacher is the owning side. You can do it by removing the student from all teachers to which it is associated, but that could lead to loading lots of data (all associated teachers with all their students). That's why introducing a separate entity for the association table could be a good compromise, as already suggested by #Mark, and as I suggested as well in some of my previous answers on similar topics together with some other potential improvements.

You may create a new entity TeacherStudent for the relationship, and then use CascadeType.REMOVE safely:
#Entity
public class Student {
#OneToMany(mappedBy="student",cascade={CascadeType.REMOVE})
public Set<TeacherStudent> teacherStudents;
}
#Entity
public class Teacher {
#OneToMany(mappedBy="teacher",cascade={CascadeType.REMOVE})
public Set<TeacherStudent> teacherStudents;
}
#Entity
public class TeacherStudent {
#ManyToOne
public Teacher teacher;
#ManyToOne
public Student student;
}
You'll have to take care of the composite foreign key for TeacherStudent. You may take a look at https://stackoverflow.com/a/29116687/3670143 for that.
Another relevant thread about ON DELETE CASCADE is JPA + Hibernate: How to define a constraint having ON DELETE CASCADE

As you see above every Student is related to every Teacher.
The point is when in a situation where "every A is related to every B", then there is no need to have a many to many table to keep such relationship. Since logically A and B is independent to each other in this situation. Adding/Deleting/Modifying A makes no effect on B and vice versa. This behaviour is exactly what you are after, because you want the cascading operations stop at the relation table:
delete cascade functionality targeting the Student_Teacher-table only!
Relationship table is only useful when in situation where "every A is related to a subset of B".
So to solve your problem is actually a fairly one: Drop the Student_Teacher table.

As we had a similar problem but finally solved it another way, here is our solution :
We replaced
#ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
in our relationship with
#ManyToMany(fetch = FetchType.LAZY, cascade = {
CascadeType.DETACH,
CascadeType.MERGE,
CascadeType.REFRESH,
CascadeType.PERSIST
})
and it successfully removed the association without removing linked entity.

JPA Inverse Join with OneToMany causing More than one row with the given identifier

I have a convenient relation set up in which an entity has a one-to-many relationship with another, and that has a many-to-one with another. So, a LISTING has many LISTING_LINE_ITEMS, and those LISTING_LINE_ITEMS have one SERVICE_PERIOD, but a SERVICE_PERIOD has many LISTING_LINE_ITEMS. I have attempted to describe this relationship using JPA's #JoinTable as follows:
LISTING
#OneToMany
#JoinTable (name = "LISTING_LINE_ITEM", joinColumns = #JoinColumn (name = "listing_id"), inverseJoinColumns = #JoinColumn (name = "service_period_id"))
Set<ServicePeriod> servicePeriods;
LISTING_LINE_ITEM
#ManyToOne (fetch = FetchType.EAGER)
#JoinColumn (name = "listing_id", nullable = false)
Listing listing;
#ManyToOne (fetch = FetchType.EAGER, cascade = CascadeType.PERSIST)
#JoinColumn (name = "service_period_id")
ServicePeriod servicePeriod;
SERVICE_PERIOD
#ManyToOne
#JoinTable (name = "LISTING_LINE_ITEM", joinColumns = #JoinColumn (name = "service_period_id"), inverseJoinColumns = #JoinColumn (name = "listing_id"))
Listing listing;
The obvious goal is to be able to easily obtain a list of ServicePeriods for a Listing or a single Listing for a ServicePeriod. Currently the way this is set up I'm getting an exception:
org.hibernate.HibernateException: More than one row with the given identifier was found: 361951, for class: com.gonfind.entity.ServicePeriod
I believe this is because a listing has ListingLineItems that refer to the same ServicePeriod. I'm sure that there is a way to accomplish what I'm after but I don't know what it is.

You do appear to have some problems there. On the technical / JPA side:
you cannot use LISTING_LINE_ITEM both as a join table and as an entity table. There are several reasons for this, but the main reason is that you will confuse JPA: it will try to use that table in different, incompatible ways for those two purposes.
in JPA, a bidirectional relationship is owned by exactly one side; the other side uses the mappedBy attribute of its relationship annotation to reference the owning side.
But you also have data design problems. Your constraint that line items' service periods be restricted to one of those separately associated with the same listing constitutes either
a functional dependency between non-key fields, if the listing id is not part of the line item key, or otherwise
a functional dependency on a subset of a key.
In the first case, your data fail to be in third normal form; in the second case they fail to be even in second normal form. Your trouble modeling this with JPA arises in part from the low level of normalization.
Normalizing your data properly would make things a lot easier on multiple levels. To do that, you need to remove the direct association between listings and line items, and instead associate them through service periods. You then would have:
Listing <-- one to many --> ServicePeriod <-- one to many --> LineItem
Of course, that would have implications on the structure of your application, but it's likely to be a long-term development and maintenance win, and maybe even a usability win, for the application to be aligned with the natural structure of your data like that. If you wish, you could put methods on your Listing entity to allow ListingLineItems to be managed to some extent as if they belonged directly to Listings, and vise versa.
That data organization would look something like this:
LISTING
#OneToMany(mappedBy = "listing",
fetch = FetchType.EAGER,
cascade = CascadeType.PERSIST)
Set<ServicePeriod> servicePeriods;
SERVICE_PERIOD
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name = "listing_id")
Listing listing;
#OneToMany(mappedBy = "servicePeriod",
fetch = FetchType.EAGER,
cascade = CascadeType.PERSIST)
Set<ListingLineItem> lineItems;
LISTING_LINE_ITEM
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name = "service_period_id")
ServicePeriod servicePeriod;
If you cannot restructure your data more or less that way, then you're stuck jerry-rigging something that cannot fully be described to JPA. I'm imagining a separate join table for Listing <-> ServicePeriod, a non-JPA FK constraint to that table from the entity table for line items, and, of course, proper form for the various bidirectional relationships.

#ManyToMany relation not save

I have some entities with#ManyToMany relation:
#ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
#JoinTable(name = "buses_drivers",
joinColumns = #JoinColumn (name = "driver_id_inner", referencedColumnName = "driver_id"),
inverseJoinColumns = #JoinColumn (name = "bus_id_inner", referencedColumnName = "bus_id"))
private List<Bus> buses;
and
#ManyToMany(mappedBy = "buses", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private List<Driver> drivers;
When execute saving Driver model with some Bus models, all ok. Tables buses_drivers store all keys those entities. But when saving Bus model with drivers, table doesn't change. I think problem with inverseJoinColmns mapping.

That is the expected behaviour. In a bidirectional many-to-many association one side has to be the inverse side. In your case it is the Bus side because it contains mappedBy:
The field that owns the relationship. Required unless the relationship
is unidirectional.
That means that Driver is the owner of the association and Hibernate will only check that side when maintaining the association.

You should definitely redesign your relations.
Without even getting into the problems with your current save scenario, with bidirectional #ManyToMany + CascadeType.ALL, you're destined to get even more troubles.
For example, deleting one bus will due to cascade, delete all its drivers, which due to cascade again, will delete all its buses. You'll basically end up deleting much more than you probably want. Also, check the SQL generated by these mappings, you'll most likely notice that its far from ideal.

For people doesn't understand from the accepted answer. This is more appropriate : Java: saving entities with ManyToMany association
I came across with this problem in test cases when filling test data.
When there is an owning side you just can save child just with owner.

Hibernate one to many mapping with additional relation table

I want to have two tables with one to many relation that are linked by third table. How can I approach this? I want to create exactly the same thing as in this tutorial but using one-to-many instead of many-to-many with unique="true"

In Hibernate when you use a #OneToMany annotation without stating a #JoinTable or #JoinColumn a third table will be automatically created to map the relationship, so no worries in just switching the #ManyToMany by #OneToMany, as long you relationship will follow the rules of the annotation.
However, you can try some explicit mapping, so you will be able to control even de column names that will be created by the #OneToMany annotation.
Try something like this:
public class TestClass1 {
#OneToMany
#JoinTable(name = "ADDITIONAL TABLE NAME", joinColumns = {
#JoinColumn(name = "TESTCLASS1_ID")}, inverseJoinColumns = {
#JoinColumn(name = "TESTCLASS2_ID")})
private List<TestClass2> listTestClass2;
}
Good luck!

How to define many-to-many to itself in JPA?

I'm trying to define this SQL schema in JPA:
TABLE event (id INT)
TABLE chain (predecessor INT, successor INT)
In other words, every event has a number of successors, which are events themselves. I'm trying to do it this way in JPA:
#Entity
public class Event {
#Id Integer id;
#ManyToMany(cascade = CascadeType.PERSIST)
#JoinTable(
name = "chain",
joinColumns = #JoinColumn(name = "successor"),
inverseJoinColumns = #JoinColumn(name = "predecessor")
)
private Collection<Event> predecessors;
}
#Entity
public class Chain {
#Id Integer id;
#ManyToOne(cascade = CascadeType.PERSIST)
#JoinColumn(name = "predecessor")
private Event predecessor;
#ManyToOne(cascade = CascadeType.PERSIST)
#JoinColumn(name = "successor")
private Event successor;
}
Is it correct?

Normally one would not both define a ManyToMany with a JoinTable and then also separately define the join table as its own Entity. Join tables aren't Entities normally, they're just join tables and the provider manages them under the hood. You're creating a lot of headaches for yourself as far as properly maintaining in memory state of the application when you change one or the other. (Which is necessary if, for example, you want to use L2 caching.)
So, either one works fine, combined, they are sort of oddsauce. Usually if you defined Chain as an entity, you would just have a list of Chain on the Event. Not also redefine it as a JoinTable on Event. Does that make sense?
(and as it is currently strictly defined, it will break if you try to make changes through the collection on Event unless that ID is a database generated sequence.)
Edit: something like this -
#Entity
public class Event {
#Id Integer id;
#OneToMany(cascade = CascadeType.PERSIST, mappedBy="successor")
private Collection<Chain> predecessorChains;
}
What you wrote originally can be made to work as long as you realize that the Collection<Event> predecessors is inherently read only and will get fubared if you try to L2 cache it. The fact that you put a CascadeType on it makes one thing that you wanted to be able to add and remove Events to/from that, which will explode when hibernate tries to execute illegal SQL.

If you use #ManyToMany, you don't need Chain entity (otherwise, if you need Chain entity, for example, to store additional data associated with the relathionship, you need to declare two one-to-many relationships between Event and Chain).