Entity bean primary key generation


EJB programming & troubleshooting: Entity bean primary key generation

  1. Entity bean primary key generation (2 messages)

    I am using CMP for Entity Beans.

    Say I have three attributes in my bean called Book namely "bookID", "bookName", "author"
    each of which map to a database column in a table called tblbook.

    There is a create method in my home interface that accepts all above three attributes as arguments like this

    Book create(String bookID, String bookName, String author ) throws CreateException, RemoteException;

    For this I have a corresponding ejbCreate in my Bean class and all the set/get methods are abstract in this class

    String ejbCreate(String bookID, String bookName, String author ) throws CreateException, RemoteException

        return bookID;

    I know the container has the job of making a new database entry everytime I call create from my home by providing some kind of implementation to these abstract methods.

    My problem is this. I want to pass only two parameters in my create i.e. I want to pass only bookName and author.

    I want bookID be automatically generated as a unique number using an oracle sequence. Since my set method is abstract I don't know exactly what to do.

    I also want to avoid 2 database hits. I will be calling the entity bean from a session bean. I dont want the entity bean to call back a session bean again just to retrieve a unique ID from the DB.

    How do I create an instance of my entity bean with an automatically generated bookID?
  2. Entity bean primary key generation[ Go to top ]

    A lot of containers now have the ability for Entity beans to retrieve their primary key from a sequence.

    For instance Weblogic 6.1,


    If your container does not support this there is nothing stopping you from making a sql call from within the Entity bean,

  3. I have used two different methods quite successfully.

    1. Generating a key in the code using a GUID generator to use as a key.
    2. Using the sequence generator session bean supplied as part of the JBOSS 3.0 template wich can be downloaded from


    The sequencegenerator bean is quite simple it has essentially one method called getNextNumber(String pSequenceName), it maintains a table with and entry for each Sequence you want to maintain the method merely gets the current number from the table adds 1 and returns the value to you.

    The main differences between the two are the GUID method does not create a sequence (assuming you care) it is essentially a random distribution but it has the advantage of not requiring any database access.

    I did make a simple change to the template code and modfied it to use a local versus remote interface because it is alot faster.