One to many unidirectional relationship in hibernate vs sleep

java - Difference between using @OneToMany and @ManyToMany - Stack Overflow

one to many unidirectional relationship in hibernate vs sleep

Map OneToOne, OneToMany, ManyToOne, and ManyToMany relationships to the .. Provides example of one-to-one unidirectional relationship posavski-obzor.info try { posavski-obzor.info(1);} catch (InterruptedException e) {}. tags: DEV, posavski-obzor.info, NHibernate, parent/child relationships. 59 comments. One to many relationships in a relational model is probably the most To map the “foreign-key relationship” between Order and Customer you a bidirectional relationship, you have to specify both the many-to-one. Note that navigational access is not always good, especially for "one-to-very- many" and "many-to-very-many" relationships. Imagine a Group.

On the other hand, an OrderLine is not very meaningful without its containing Order. Therefore, the OrderLine will probably be a Component of the Order entity. This definition is somewhat abstract and vague, as it depends on the context.

one to many unidirectional relationship in hibernate vs sleep

To be more concrete, I usually use the following question to determine whether a class is an entity or a component: Does the application allow the user to search for a particular instance of this class? NHibernate uses this Id to correlate between instances of the the class in memory and the row in the database.

Therefore the only way NHibernate can update the database to reflect the changes is to delete all of the children of that parent, and then re-insert all of the children one by one.

one to many unidirectional relationship in hibernate vs sleep

This is a significant drawback in terms or performance, and therefore NHibernate came up with a special type of collection called idBag. Note that this column is not associated with a property on the class! This is how it looks like: Note that for components, this happens automatically, but often you want this to be the case even if the children are entities.

Best Practices for Many-To-One and One-To-Many Association Mappings

Recall the definition of an Entity: Of course that you can call ISession. You just need an attribute that maps the association and a OneToMany relationship.

one to many unidirectional relationship in hibernate vs sleep

You probably expected that Hibernate would only persist a new Item entity in the item table. I did the same when I used this mapping for the first time. Why does Hibernate execute so many queries and introduce an additional association table? In your table model, you normally use a foreign key column on the to-many side of the association to store a reference to the associated record.

Hibernate uses the same approach when you model a bidirectional one-to-many or an unidirectional many-to-one relationship.

Understanding One to Many relationships in NHibernate | Arnon Axelrod's Blog

It uses the foreign key column to map the association. So, Hibernate introduces an association table to store the foreign keys. You can avoid this table if you specify the foreign key column with a JoinColumn annotation. This column has to be part of the table of the to-many side of the association. So, better use a bi-directional instead of a unidirectional one-to-many association. Avoid the mapping of huge to-many associations I know, mapped to-many associations are useful, especially when you want to join entities in a JPQL query.

But Hibernate loads all associated entities when it initializes the association. That can take several seconds or even minutes when Hibernate has to fetch several thousand entities. So, better use an unidirectional many-to-one association. That allows you to fetch a number of entities that you can handle in your business logic or present to the user. Think twice before using CascadeType.

one to many unidirectional relationship in hibernate vs sleep

Remove Cascade remove is another feature that works well on small to-many associations. Using it for one-to-many or many-to-one associations is not as dangerous as it is for many-to-many relationships.

one to many unidirectional relationship in hibernate vs sleep

The following mapping tells Hibernate to remove all associated Item entities when it deletes the PurchaseOrder entity. So, Hibernate needs to select all associated Item entities and remove them one by one. Deleting the associated entities one by one can create an overhead that is huge enough that you should better remove them with a JPQL query.