JPA Study - Chapter 2

jpastudy

1. Obtaining an Entity Manager and Persisting an Entity
EntityManagerFactory emf = Persistence.createEntityManagerFactory("EmployeeService");
EntityManager em = emf.createEntityManager();
Employee emp = new Employee(130);
em.persist(emp);

persist가 완료되면 emp 객체는 entity manager의 persistence context에의해 관리된다.

2. Finding an Entity
Employee emp = em.find(Employee.class, 130);

못찾으면 null return.

3. Removing an Entity
Employee emp = em.find(Employee.class, 130);
em.remove(emp);

emp가 managed instance여야함.
emp가 null이면 IllegalArgumentException 발생.

4. Updating an Entity
Employee emp = em.find(Employy.class, 130);
emp.setSalary(emp.getSalary() + 1000);

emp가 managed instance여야함. 아니면 persistance provider가 값의 변경을 인지하지 못 함.

5. Transaction
em.getTransaction().begin();
Employee emp = new Employee(130);
em.persist(emp);
em.getTransaction().commit();

6. Queries
TypedQuery<Employee> query = em.createQuery("SELECT e FROM Employee e", Employee.class); //JPQL임
List<Employee> emps = query.getResultList();

7. persistence.xml Example
<persistence>
 <persistence-unit name="EmployeeService" transaction-type="RESOURCE-LOCAL">
 <class>examples.model.Employee</class>
 <properties>
   <property name="javax.persistence.jdbc.driver" value="org..." />
   ...
 </properties>
</persistence>

in the META-INF directory