The question is that what does it save?
Only the entity?
The entity and it's relationships?
Does it saves the relationships and the other end of those relationships?
Or does it save everything that the entity contains recursively and it acts as an anchor node?
It saves the entire subgraph that you have, the entity you're calling the save() on acts as an anchor node. In other words, the save() function operates recursively, so changes made to any connected nodes or relationships will be saved as well.
The relationships and nodes that are not in the subgraph won't be affected.
Related
TL;DR: Is it enough to call repository.save() on the owning entity to persist the relationship or do I need to save both entities?
Let's say I have two entities, A and B and a oneToMany relationship between them. A can have multiple B's, B can have an A. B is the owning side of the relationship (has the foreign key). If I have two, already persisted entities and want to add and persist a relationship between them, then I typically do this:
a.addB(b);
b.setA(a);
bRepository.save(b);
My question is, do I also need to call aRepository.save(a)? Thanks in advance, Googling didn't help me to find the answer.
If as you describe the relationship is owned by B, A didn't change at all as far as JPA is concerned. So it doesn't need to get persisted.
If you have persisted or loaded A and B in the current session, no save at all is technically necessary. JPA keeps track of the entities, note that they are changed and will flush the changes to the database at the end of the transaction.
Good question and assuming that you have already saved the A entity the answer should be that you do NOT need to save the parent A entity again since you have added the child entity B to A's list of children yourself and A is already persisted.
If you ever reload A and all its children you should get the same list as you currently have.
Since it is lazy loaded your query should specifically load the children in the case you want that otherwise you might get into the situation where you assume that A has all its children but you doesn't if you reloaded A from the database without getting them.
In general though I have to question why you are keeping A around in the first place. Caching can be a good thing but your cache should refresh A when its children are updated and should fetch all of A's children if that is what is needed. In that case you don't need to add the new child to A yourself b/c it will be overwritten anyway. Probably doesn't hurt, but why do you want to second guess the cache?
More generally the pattern is simply to save B and be done with it. If your code needs A and all its children it should fetch from the database when needed.
These thoughts do not include JPAs entity cache since I have not attempted to get into very specific detail about that.
I have an entity that has a Set of child entities. Can I add/remove some of the children in the collection in Hibernate's org.hibernate.Interceptor.onFlushDirty()?
The documentation (javadoc, JBoss userguide) doesn't explicitly mention changing relationship state, so I just want to make sure it's legitimate.
Update
Decided to describe by problem.
There's a Parent entity that has a Set of Child entities. The Child entities are created based purely on fields of the Parent entity, no additional information needed. The children need to be updated each time before persisting the Parent.
I wanted to do it in Interceptor.onFlushDirty() by clearing existing children and adding new reclaculated (i.e. Transient) children, but I'm getting the TransientObjectException. As I understand, it's because I add transient Child entities during flush, but I'm not sure.
I have an entity(ex: Document) that is used as child in 4 other entities(using #OneToMany with #JoinTable in parents). I am not using Bidirectional Mapping. My requirement is to remove the Child(i.e Document), and I have two ways to do that, one way is, get the 4 parents, remove child from them and update them. Second, using native query(using jdbcTemplate) to remove entry from 4 join tables and remove the child.
Is there any other way it can be done in much simpler manner?
Create an abstract base class containing the Document as member and user JPA inhertiance --> http://en.wikibooks.org/wiki/Java_Persistence/Inheritance
Than it should be possible to get all users of a document with just one query.
Than it should be relatively easy to remove all references.
Don't do magic behind automatic deletion stuff. Thats for the cost of documentation.
Add orphan deletion (ie. delete child object when it's removed from collection in the parent). To enable it, you need to add
#OneToMany(orphanRemoval=true)
in owning entity.
I would like to know is there any way to use complex type to insert data in more than one table
if I have a parent object has a collection of child object and I need to insert data in the parent and its child too
Example: This is the parent object "Video" and its Child VideoData Diagram
Please advice
EF will update all modified entities/properties automatically. So if you create a new VideoData, set it's language, and append it to the VideoDatas collection of a Video instance, then call
context.SaveChanges();
EF will add the VideoData to the db, setting the Language, then update the Video record. It walks up and down the graph saving any changes. You just need to make sure you are using context to get the entities in the first place so EF can track it.
I have a core data entity which has an exclusive one to many relationship with another entity. This relationship is supposed to be a basic containment the first entity contains one or more of the second. An instance of the second entity can only be contained in one of the first entities.
I want to be able to remove all the contained entities from the first entity and then delete them. How should I do this? Should I remove the relationship and then call deleteObject for each entity or will calling deleteIObject for each contained entity cause the relationship to be set correctly. If the second is true, can I just enumerate the contained entities and call deleteObject or should I first make a copy of the set (if calling deleteObject for each objects severs the relationship this will modify the set which is not allowed in normal enumeration).
Delete each child object via the NSManagedObjectContext and the relationship will clean up appropriately. This is assuming that you are following the convention and have all of your relationships configured to be bi-directional.