save parent in hibernate with child - java

I am lil bit confused in hibernate,
Here i am having one parent object and this parent object (Suppose A is a parent and B is child object) has many to one unidirectional relation with child object B.
Now, I have a object A along with Object B . What i have done is , i saved all the child objects in database, so now every child objects are saved in db and have id .
Now i want to save parent object A for its related child object. How can i do that ?
Though it might be very simple for u guys, i am new to hibernate. so need lil help.
Thanx in advance. :)

Why are you saving parent and child separately? Set the child to parent and merge the parent. Underlying ORM technology will take care of rest. But just add cascade type PERSIST and MERGE (ideally PERSIST is enough, but MERGE handles updates as well) over the relationship in parent entity.

Related

Querying/Selecting rows from Parent Entity when using Hibernate JOINED inheritence strategy

I know there are three types of inheritence strategies: SINGLE_TABLE, TABLE_PER_CLASS, JOINED. I think the best choice is JOINED if I want my underlying database to be normalized. However, let us consider this usecase: I have a Parent Entity and one Child Entity that extends this Parent Entity. The inheritence strategy I am using is JOINED. Now, from the front-end of the application I can add Parent and Child entities. When I do search from front-end to get all Child Entities I am able to get all the Child Entities. Now, when I try to do a search only on Parent Entity I see that the result set contains all the entities(Parent + Child) and I understand why this is happening. My question is that is there any way we can search/query for only Parent entities(excluding rows from Child entity) when I am using the JOINED inheritence startegy?
Newer versions of Hibernate optimize this, but you have to make sure you are not selecting the entity or use fields of the parent table.

hibernate one-to-many child updating

I have a parant entity Project and child entity Task(onetomany relationship). I would like to know how update child right. All examples I found are with one table.Thanks
What exactly do you need here? if you want to update the child of current parent then iterate through the child list / set and then modify the appropriate child within that for each loop. You could also update your parent too. so here when you flush / commit your transactions your parent table and the child tables as well get updated successfully.

Hibernate - Updating an ID of a parent in a child without updating parent?

I couldn't find the answer or didn't phrase this question properly. If you guys know... let me know :-)
I have a parent which has children....
on the child, I have regular vars that map to column names
However, one is mapped as many-to-one. The child basically contains the ID for the parent. Except in the child I obviously contain the entity of the parent, not the id.
ie: (QUICK simple example....)
#ManyToOne(fetch= FetchType.EAGER)
#JoinColumn(name="bcId",referencedColumnName="id")
private ParentEntityClass theParentClass;
How, can I set the the parent object in this hibernate entity so it ONLY uses the parent entity for the ID and doesn't try to save the parent. Should I use Cascade.refresh so it refreshes but doesn't update the parent?
Thanks :)

Disable update to many to one entity in hibernate

I have a Parent and Child entity. Child has a Manytoone annotation to reference Parent. The use case is that when i load a child by findById and get the parent out using the getter. then If I update the parent, I am able to save the parent. I do not want the parent to be updatable which is pulled out from a child.
I want only to update parent if I directly find it by id and change attribute and save.
I know hibernate has no info when i do getParent() from child that it got it from child and not find by id and makes an update to parent.
I tried Immutable annotation on ManytoOne on Parent but it does not prevent an update to be fired.
Is there any way that I can make the parent pulled out from a child non-updatable?
feel free to ask any clarifications.
The problem you are experiencing, in fact belongs to the Hibernate Session. It has nothing with Cascading. Because the session is designed to be a unit-of-work for us.
Whenever you access an object 1) by ID or 2) by reference, this object is (from that moment) "cached" in the Session. It is one instance shared accross all the handling during the Session life-time.
So, once, the Parent is loaded into session, and you are amending it anyhow, and later Session is flushed - any changes to Parent are persisted.
You can call session.evict(parent) explicitly, to avoid changes propagation during the Flush.
But It seems to me a bit weird, that you are changing the Parent (accidently...maybe) while working with child and not willing to store these changes. Other words, maybe solution is to change the approach.
You can call EntityManager.detach() on the parent that you obtain through the getter. Any change made to the detached entity will not be synchronized to the database.

three layer of data, Parent-Child-Grandchild

I have a hibernate issue where I have three layer of data, Parent-Child-Grandchild, Parent to Child one to many and child to grand child one to many. I am unable to save data when I say parent save (hibernate session save method), I use cascade.ALL. I am able to save two layer, parent to child one to many. What I need to do in this case. I have one parent record which has two child records and each child record has three grand child record. Please help.
You need a Self Reference One-to-Many relationship. It does not matter how many levels you need.
Here is a good tutorial which can guide you:
http://viralpatel.net/blogs/hibernate-self-join-annotations-one-to-many-mapping/

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