If i havea JPA class Person and Person has reference to a JPA class Address. If I call Person.persist(), will Address.persist() be called implicitly?What if the hierarchy was longer. Would all the child classes be persisted implicitly?
From the JPA specification:
The semantics of the persist operation, applied to an entity X are as
follows: ...
the persist operation is cascaded to entities referenced by X, if the relationships from X to these other entities is annotated with the
cascade=PERSIST or cascade=ALL annotation element value or speciļ¬ed
with the equivalent XML descriptor element.
Related
I have a general utilization question on how to set up Objectbox entities for wholly owned nested objects
My app has a central data entity 'Class1'. The 'Class1' entity includes an array of 'Class2' instances. The 'Class2' entity includes an array of 'Class3' instances. Both the 'Class2' and 'Class3' entities are fully owned by a single 'Class1' entity (i.e. they are never used or linked to anything else)
What's the best strategy for mapping wholly owned nested objects in Objectbox?
If I understand correctly, this can be done using relations in ObjectBox.
E.g. Class1 would have a ToMany relation property, Class2 a ToMany relation property.
https://docs.objectbox.io/relations#to-many-relations
Entity A is marked as #Cacheable(false) and A holds a relationship to another entity class B which is cacheable by default.
#Entity
#Cacheable(false)
public class A {
// ...
#xxxToOne B b;
}
What is going to happening, when I load an A instance through the EntityManager, when the related B instance is already available in the (2nd Level) cache? Will the framework perform the JOIN on the database and load the entire information of B as well, or will it return the B instance from the Cache?
Does the FetchType influence this behaviour?
Is this clearly defined in the JPA Spec. or may it depend on the JPA vendor?
I want to copy all entities of one DbContext to another DbContext.
I am able to list all Entity types by using the Model.GetEntityTypes() method of the source DbContext.
How can I retrieve all entities of the given type from the source context, in order to add them to the destination context?
I was reading a question about EJBContext.setRollbackOnly() method in a mock exam, one of the accepted answers is
It cannot be used by JPA Entities. [because] Entities do not have EJBContext. Remember that persistent entities are not same as Entity Beans. Entity Beans do not exist in EJB 3.x.
API reference states that
The EntityContext interface provides an instance with access to the container-provided runtime context of an entity bean instance.
and EntityContext extends EJBContext.
Now, what does it mean that persistent entities are not same as Entity Beans?
I am facing a problem with EF 4.1. I am trying to Add a detached object to the DbContext. Problem is it is not the emd mapped object, but derived from it. Changing the mapping is not an option as some teams are using the model with the regular mapped BL-classes, but my project created a derived model for UI stuff. Even with casting I always receive a
InvalidOperationException ("Mapping and metadata information could not be found for EntityType ...").
What I want is EF to treat this as the base class and put the object into the DbSet of the BaseClass. The current EF code is:
Context.Entry(object).State = EntityState.Added
But I am open for other suggestions, even
via IObjectContextAdapter, as long as it can save the Base and the Supertype. This should be simple, right?! Mapping to a new Base-class instance is not good idea as the main objects temporary Id would not be updated after saving...
Thanks!
As I know this is not possible. You cannot use derived class from the entity instead of the entity. You must either map derived class as well or create new instance of the entity for persistence and copy all fields from your derived class instance to the entity instance.