So, let's say that I have an object A which has a many to many relationship with object B(B is an entity to a config table in the db which means that the values are not insertable nor updateable.
If I want to save an object A with a list of objects B, is it enough if I provide only the ID of the object B or should I do a query with the ID to get the entire object in order for JPA to do the mapping?
Thanks!
If you are using JPA you need the "complete" objects before persisting them. This means that in your case you will need to get all objects B from the database, then set them in the object A that you are trying to persist and then finally save object A.
Related
I have an Entity that has four properties, (vehicle, unit, date and id). Primary key is the ID.
I want to delete rows from the database based on the vehicle list provided to me via a request body.
How can I take all the lists and use them to delete data from the database at once?
You can create a "delete...By" query in your Entity repository that takes a List of Vehicle as a parameter and deletes all entities that their Vehicle is contained in that List.
Something like this should work:
void deleteAllByVehicle(List<Vehicle> vehicles);
The documentation contains more options:
https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#jpa.query-methods
you can use JPQL to provide custom query
#Query(delete from Entity e where e.idvehicle = :id)
void deleteByVehicle(#Param("id") int idvehicle);
now you can just pass the id of the Vehicle like that:
deleteByVehicle(vehicle.getId());
I would like to know, how to save related documents in reactive mongo ?. Because I find a code that attempts to do the magic... But when it should save the related document in another collection, it serializes inside the "father" of the relationship let say... I know that in spring data reactive mongo, #DbRef doesnt have support... How could I save the data in a way that, if I query the collection, I see that the attributesare the name of the collection and the generated id instead all of the object attributes ?.
If the pic above is seen, you will see that the attribute "user" is saved as a nested document but not in the corresponding collection. Do I need to hook in another event ?.
I had put a listener onbeforeconvert to scan every time a save operation is to be applied and save the object... How to proceed ?... think I should verify if it has a related doc from another collection and if its nonnull... If the object doesnt have any attr l
Alike, then save it... if not continue the scanning... dunno
My question is would Spring JPA throw exceptions for every query?
I mean, let say there are tables without any relation (FK) between them in database. It is bad design but you cannot change it and it is not up to you.
But you know that data itself should be as there are relations.
That's why you create Entity model with all relations like they are there.
But as I said there is no real relations in database.
And in one point data are inconsistent in database.
Would Spring JPA throw exceptions if there are inconsistency or it will just return you inconsistent data?
I assume with "relations" you mean "foreign keys".
JPA doesn't care about foreign keys.
All it cares about is if the data matches the mapping information on the entities.
So if you have an entity A that references an entity B with id b but such a B does not exist you might eventually get an exception.
Or you might just get an A with a null reference to B.
If the reference is marked as mandatory you might actually not be able to load the A in the first place, because a join is used and therefore not returning any data at all.
Side note: All this depends more on the JPA implementation you are using than on Spring Data JPA.
To the question "Save Differences with Entity ID" I found the following answer:
"For Entities, Id property cannot be null, so you need to map this class as ValueObject. If so,
Id property is treated as regular property and it not goes to GlobalId of this object."
My question is:
Why can't an entity be treated as NEW if the Id is NULL?
I have an object graph that is fetched from the database, and between two javers commits an entity is added to a list in the graph.
Two commits and in the second commit there is a new entity (Id NULL)
Get the change => exeption because Javers can't create a GlobalId.
I can get arround this by doing EntityManager - persist (creates Id:s), but I would like to avoid doing that. The present code may do a persist later or it just lets the transaction finish.
Because the Id is NULL, the entity is NEW. Would it be possible to generate a unigue temp Id (allow Id = NULL) to be able to create the GlobalId?
In the change list, the entity would be reported as NEW. No need to compare with earlier commits.
You should compare/commit your objects when they are fully initialized so when they have Ids.
An entity without Id can't be handled by JaVers for several reasons:
it can't be compared to other entity/version (diff algorithm is based on GlobalIds)
it can't be queried from JaVersRepository (queries use GlobalIds)
If you are using Hibernate, compare/commit your new objects after Hibernate assigns them Ids from sequences.
Another options:
don't use sequence-generated values as JaVers Id but some business identifiers
if an Entity doesn't have a business identifier you can generate UUID in a constructor and use it as JaVers id (and also database PK if you like)
I have a method that creates a #Transactional and fetches some entities A and creates some entities B that have relationship to A.
Inside this method, I need to persist an entity C that has a #ManyToMany relationship to A, however this persistence needs to happen no matter what, so in the save method of C's repository, I add a #Transactional(propagation=Propagation.REQUIRES_NEW).
The problem is when I try to persist C, the A's in the relationship are in another Session.
Is it possible to save C and it's ManyToMany relationship table without attaching A to the session? All the A's in the relationship have have been already persisted hence they have ids, and that is all I need to persist in the auxiliary table.