Java EE 8 Application Development

Entity relationships

In the previous section, we saw how to retrieve, insert, update, and delete single entities from the database. Entities are rarely isolated; in the vast majority of cases they are related to other entities.

Entities can have one-to-one, one-to-many, many-to-one, and many-to-many relationships.

In the CustomerDB database, for example, there is a one-to-one relationship between the LOGIN_INFO and the CUSTOMERS tables. This means that each customer has exactly one corresponding row in the login info table. There is also a one-to-many relationship between the CUSTOMERS table and the ORDERS table. This is because a customer can place many orders, but each order belongs only to a single customer. Additionally, there is a many-to-many ...