Use of ejb BD implementation provided by Mandragora

Right now, the only ejb implementation of BD provided by Mandragora is just stateless session beans implementation, but it is not hard to write the right implementation for other kind of ejb beans. The ejb stateless session bean implementation of BD is:

So if in your class you want to use this BD implementation you have for example to do:

and put the following in Mandragora.properties.

The SLSBManagerBD uses ejb session facade bean in place of pojo facade bean. Concretely it uses the ejb beans BusinessSLSBFacadeHome and CrudSLSBFacadeHome. To make SLSBManagerBD use these two beans you have to specify their use in Mandragora.properties, adding (if they are not yet) the following entries:

The two beans together have the same methods (the same signatures) of the BD interface.
Both BusinessSLSBFacade and CrudSLSBFacade beans use a ServiceFacade implementation to make their job. To specify which is the ServiceFacade implementation the user wants to use, the following four entries have to be added to Mandragora.properties (See lookup and mapping section).

or, of course other ServiceFacadeFactory concrete extensions and ServiceFacade implementation can be specified.

The main difference between SLSBManagerBD and PojoManagerBD, is that the PojoManagerBD uses directly a ServiceFacade implementation (for example it.aco.mandragora.serviceFacade.pojoFacade.PojoFacade) to make its job, while the SLSBManagerBD delegates its job to the two session beans that in turns use a ServiceFacade implementation. At the end it is always the ServiceFacade doing the job, but in the SLSBManagerBD case, the same job is done inside the Ejb container. For both ejb session bean BusinessSLSBFacade and CrudSLSBFacade the transaction type is Container, and their methods have transaction attribute required.

Add methods to ejb BD implementation

Mandragora's user, or client, has access to many business delegate methods trough the interface BD.
The user can write its own BD implementation, extending for example some provided one(see how to extend). All the methods provided are transactional, that means that each one of them is executed in one transaction. But the user can need to use two or more of that methods in the same transaction. For example it could need to do something like this:

All in one transaction, with the isolation level he wants.

The BD interface provide lots of generic methods, the most useful, and the idea is to make its number growing up, so that the user has always more probabilities to find out the method he needs for his purposes already written. Of course in every application always there will be some business method that belong to the core business logic of the application that can't be generalized, and that is impossible to find in the list of generic methods. Even so the most probable is that the method we need to write can be expressed in terms of the existing ones. Let's see now how, with the help of the Ejb container, how can such new methods be executed in one transaction.

All that we have to do is to make a new ejb bean with the new methods, then write an extension of SLSBManagerBD with the new methods, and expose it to the user registering it in Mandragora.properties. Let's see it in detail.

Distributed transactions

In this section we show how we can extend BD with a method to insert in two different databases in an unique transaction.
First of all we have to extend the BD interface with the new wanted methods.

The second method insertInTwoDBAndRollback has just testing purpose.\

Now we have to write an implementation for UserExample2BD. We will extend the SLSBManagerBD.

Let's have a closer look at userExample2SLSBFacadeHome.
It is looked up through the ServiceLocator method

• getEJBHome(Utils.getStringFromMandragoraProperties("UserExample2SLSBManagerBD.userExample2Manager"))

so in Mandragora.properties there must be

In the ejb-jar.xml we have to add under <enterprise-beans>

and under <assembly-descriptor>

In the following we show the UserExample2SLSBFacade, UserExample2SLSBFacadeHome, and UserExample2SLSBFacadeBean

What you should note in the UserExample2SLSBFacadeBean are the following lines of code in the method insertInTwoDB:

To have an idea of what ContextHandler and localSession have a look at advanced/context.html.
Here you have just to know that ServiceFacade looked up is a ProxyServiceFacadeHandler; this means that the ServiceFacade implementation is a ContextHandler instance as well, so it holds a localSession which parameters values will be used to do the job in place of the default ones. So putting a new jcdAlias in the serviceFacade local session we forced this serviceFacade to use the provided jcdAlias.
So the call serviceFacade.insert(insert1VO) will act on the DB specified by the input parameter dbAlias1.\

As we can see the ServiceFacade is looked up trough:

• ServiceLocator.getInstance().getServiceFacade("UserExample2SLSBFacadeBean.ServiceFacadeFactoryClass","UserExample2SLSBFacadeBean.ServiceFacadeClass")

So if we want the ProxyServiceFacadeHandler we have to put in Mandragora.properties

For further details about ProxyServiceFacade have a look at ProxyManagerBD and ProxyBDHandlerFactory that are very similar.

Further configurations

To use the ejb implementation you have to say to Mandragora that it going to work in a managed environment.
As always this is done adding an entry to Mandragora.properties

Moreover if you are using the ojb implementation of the DAO (the only one provided by Mandragora right now) you have to configure properly the OJB.properties (see http://db.apache.org/ojb/docu/guides/deployment.html#Configure+OJB+for+managed+environments+considering+as+JBoss+example).
You should read properly that documentation, anyway you have to add these entries to OJB.properties.

If you want Ojb accessible via Jndi, you should first have a look here.
If you want mandragora to use Jndi to access Ojb apis yo have to add to Mandragora.properties

PersistenceBrokerSupportJndiImpl get the PersistenceBrokerFactoryIF in this way:

So we have to bind it to the name "PBFactory".
To bind it to the name "PBFactory" you can add to your web.xml

or follow the instruction here.