Using Data Acess Command Beans as Model

Question

Hey guys,
actually I try to get data from some EJBs (Entity Beans) into my Web Dynpro application.
Inside SDN I found a tutorial which uses the 'Data Access Command Bean pattern' to connect the EJB-Backend to a WD application (The tutorial is called 'Using EJBs in Web Dynpro applications. You find it in the 'Web Dynpro Sample Applications and Tutorials' subsection in the 'SAP NetWeaver -> Application Server -> Web Dynpro' section). The author writes a 'Command Bean' which is bound to the WD application as a model. This bean has an 'execute()' method which calls two business methods from a session bean. Because of data binding the private attributes from the bean class are filled with the data in the corresponding model class.
Everything is fine so far.
But in my WD application I want to handle two or more context elements from the model node with the command bean. Therefore I guess I have to call the execute() method for every context element of the model node, cause the private attributes of the command bean will only hold the data of the current context element (that's what I assume). Well the point is that every call of execute() will result in an insert operation on the database.
In my opinion it would be a better way to give all context elements in one batch to the EJB-Backend so that the connection to the database have to be opened and closed only once instead after every call of the execute method.
I wonder now if it is possible to pass the whole context elements collection to the EJB-Backend. Did anyone have some experience with this?
Thanks in advance to all answers!
Regards,
Torben

Answer 1

You can simply provide an attribute in your Command Bean of type Collection. This can hold a collection of DTOs (<a href="http://java.sun.com/blueprints/corej2eepatterns/Patterns/TransferObject.html">Data Transfer Object</a> pattern... also known as Transfer Object or Value Object) to which you can bind a context node.
This attribute can then be populated with an appropriate collection of DTOs explicitly in your code... or optionally, you can bind a UI Element of type Table, for example to the associated context node. Then provide some functionality in your UI to make it possible for users to add elements to that table.
When comes the time to call your back-end, you can pass that collection directly to your business delegate (or Session Bean if you're interacting directly with that):
   public void execute()
    bizDelegate.insertSomething(this.getDtoCollection());