entity bean

When an entity bean stops looking like a data object and starts looking like a helper class, you know you ve got a problem.

A CMP entity bean is constructed from at least six separate files, having dependencies that cannot be easily verified at compile time.

Any object that can be returned by an entity bean (or any other EJB component) must fulfill this requirement.

Even if every method in your entity bean changed just once a year, the bean would acquire double the methods by the end of that year.

In a production environment, the CategoryData helper class can be replaced by an entity bean representing the categories.

With this strategy, WebLogic Server allocates a separate entity bean instance and enables locking and caching to be handled by the database.

Each rule is represented by an entity bean that persistently stores information related to that rule.

The entity bean is a very simple example, named Person, which has attributes firstName and lastName, and a key field named id.

This sample project consists of an entity bean, a session bean, a sample servlet, and a sample client.

It is common to have additional "finder" methods defined for a given entity bean within an application.

Database concurrency strategy causes WebLogic Server to delegate locking requests for an entity bean to the underlying datastore.

The Web browser client will never interact with the entity bean directly, not even with its remote interface.

In entity bean operation, the container handles the persistence of a bean's state, ensuring that such data has been preserved for later use.

If you assign a read policy to an entity bean, an exception will be thrown if you attempt to update it.

Upon receiving a request, a servlet calls a method on a session bean, which then invokes a method on an entity bean.

If you know that an entity bean will only ever be read and not updated, then this policy will simulate a read-only lock.

In addition, you need to have EJB entity bean deployment descriptors and a mapping file and database schema.

Try out some of the remote methods on the session bean which in turn invoke similar methods on the entity bean.

There is more than one entity bean that needs to be updated, deleted, or queried by a client in a workflow.

Of course, this also takes into consideration the transaction attributes of the targeted entity bean.

The Session Facade pattern substitutes a single call to a session bean for multiple calls to an entity bean.

Because entity beans purely represent data, it is suggested that no workflow logic be coded in an entity bean.

An entity bean represents business data and its related manipulation logic.

Thus, sometimes a session bean should access a database directly and sometimes it should access the database through an entity bean.

The use of an entity bean is purposely avoided here to simplify the configuration and setup for this example.

Pattern places a session bean between the entity bean and application clients.

This will pass execution on through to the servlet controller to the session bean on to the entity bean.

EJB references can also be defined in an EJB module for EJB-to-EJB interaction, such as a session bean calling an entity bean.

AccountValue -- a transfer object that represents account information obtained from the Account entity bean remote interface.

They all have lock hints described by their name, wsPessimistic#hint#, where #hint# further describes our intention with the entity bean.

With one-to-many relationships, an entity bean uses a Java collection to represent the many side.

This session bean acts on the customer data by referencing an entity bean to perform the basic database operations.

Listing 15 shows the assembly-descriptor from a sample EJB application with an entity bean.

For instance, when the user clicks a button to submit a JSF form, Seam automatically parses the form fields and constructs an entity bean.

It does not map table relationship to CMP entity bean relationship.

EJB finders can be defined on a container managed entity bean using the EJB Visual editor.

Java Persistence Architecture API: Defines the new entity bean model for persistence.

The ORM in CMP generates mapping code between the CMP entity bean and tables.

It does not map table inheritance to CMP entity bean inheritance.

A common solution to the type of problem described here is to simply add the helper method to the entity bean itself.

The relationship is represented by a new CMP entity bean called Attendee, having two fields (three if we count the primary key field).

These details are handled by the container in entity-bean development.

The EJB container is important for maintaining the referential integrity of all entity bean relationships.

Persistence API: Defines the new Entity Bean model for persistence.

Listing 2 contains the standard Java deployment descriptor for this entity bean.

To clarify this, look at Figure 1, which depicts the initial (Remote Entity Bean) implementation of the use case.

The User EJB, an entity bean, then performs the work of actually adding the user to our database.

Experimental task: design an entity Bean, a query to the database.

In part I, step 7 you generated deploy code for the process and an entity bean was created.

This method can be used only for an entity bean.

Listing 3 covers the Geronimo-specific companion file for this entity bean.

Then, Seam passes the entity bean into the event handler session bean, which is also created by Seam, for processing.

This forced us to manually move attribute values to and from the CMP entity bean and our own entity object.

The class diagram shows the attributes for each entity bean.

This method returns an entity bean for the cart table row with the given CartId.

In this case, the session bean will perform a lookup on the entity bean.

For each of the tables an entity bean is defined.

The first method, findEmployeeRec, takes an argument and simply invokes a method on the entity bean to get the EmployeeRec wrapper type.

CMP entity bean update is not efficient because it requires a read from the database and then an update in the database.

In this code, we get the account ID from the entity bean BankAccount, and then set the appropriate parameters on the CallableStatement.

Figure 5 illustrates how an entity bean would manage the Make Payment use case.

Closer to home, which is best: a stateless session bean, a stateful session bean, an entity bean or a message driven bean?

A session bean can access data directly from the database or it can invoke methods on an entity bean to do the same.

In Listing 8, you can see the specification of the entity bean's persistent fields.

That is, if concurrent transactions update an entity bean with same primary key, updates could get lost.

For example, for an update operation, you need to get JNDI context, look up EJB home, find the EJB entity bean and then update the bean.

We used EJB2 CMP entity bean life-cycle events before inserting and updating a record into a table.

Defines the entity bean that is deployed inside the container.

Research and Implementation of the Container Managed Persistence of Entity Bean

Figure 9 shows how to specify the data source for each version of an entity bean at deployment time.

Add the following remote methods to talk to the HelloWorldEntity entity bean

Here are the CMP entity bean issues we found