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Table of Contents
Hibernate is the implementation of the Java Persistence API.
Annotations
Tutorials: http://viralpatel.net/blogs/hibernate-one-to-many-annotation-tutorial/
In examples there is:
- One Department has many employees
- One Employee has one deparment
ACHTUNG:
- Bei OneToMany, ManyToOne bezieht sich der erste Teil auf die Klasse, in welcher die annotierte Variable befindet.
Wenn wir in der Klasse Department das Set employees annotieren - dann steht dort @OneToMany. Weil One Department Many employees hat.
@ManyToOne
Then the modelling will look as following:
@Entity
@Table(name="EMPLOYEE")
public class Employee {
@ManyToOne
@JoinColumn(name="department_id")
private Department department;
}
@Entity
@Table(name="DEPARTMENT")
public class Department{
@OneToMany(mappedBy="department")
private Set<Employee> employees;
}
Discriminators
Discriminators are used for for storing class hierarchies in a single table. If having RedCar.class inheriting from Car.class - both stored in one table, then discriminator tells - hwne t orestore a RedCar and when t orestore a Car.
The element is required for polymorphic persistence using the table-per-class-hierarchy mapping strategy and declares a discriminator column of the table. The discriminator column contains marker values that tell the persistence layer what subclass to instantiate for a particular row.