creating and removing entity beans

Describes the basic create/remove api for persistent entities.

Almost all applications need to add and remove entities from the database. Although most database accesses are reads, eventually we need to change the database. With Amber, you create a new instance with the following steps:

Instantiate the instance with "new"
Populate the values
Call the EntityManager ersist method

Files in this tutorial

WEB-INF/resin-web.xml	resin-web.xml configuration
WEB-INF/classes/META-INF/persistence.xml	persistence.xml configuration
WEB-INF/classes/example/Course.java	The course bean
WEB-INF/classes/example/CreateServlet.java	The create servlet

Database Schema

The example uses the same database table as the previous basic example.

create.sql

CREATE TABLE create_courses (
  id BIGINT PRIMARY KEY auto_increment,
  course VARCHAR(250),
  instructor VARCHAR(250)
);

Client Servlet

Clients create a new bean and populate the fields just like a normal Java object. The client adds the entry to the database by calling the EntityManager's persist method.

Adding and Removing Courses

...

divination = new Course("Divination", "Sybil Trelawney");
_entityManager.persist(divination);

...

_entityManager.remove(divination);
...

Demo