JPA - Part 1
This post is part of Project Digitisation. I have decided to write about JPA in several posts. This is part 1 of the series.
JPA - Java Persistence API
JPA is a specification. There are several implementations like Hibernate, TopLink etc. Persisting objects in DB is an integral part of Enterprise applications. JPA provides:- ORM (Object Relation Mapping) i.e. it maps an Object to a Relation(Table).
- An Object which can be mapped is called an Entity
- JPQL - Java Persistence Query Language
Annotations used:
- @Entity
- Used before a class name. By default, table name is same as class name.
- @Id
- Used before the instance variable which is the primary key in the table.
Example:
@Entity
public class Employee {
@Id
private int empId; //becomes primary key
private String name;
//getters and setters
}
this maps to Table: Employee
| empId | name |
| ----- | ---- |
| _____ | ____ |