Container-managed persistence restrictions and exceptions

The container-managed persistence (CMP) features have certain restrictions when used in specific ways.

 

Enterprise bean deployment and Sybase IMAGE type restriction

When deploying enterprise beans with container managed persistence (CMP) types that are non-primitive and do not have a natural JDBC mapping, the deployment tool maps the CMP type to a binary type in the database, where it is stored as a serialized instance. For Sybase, the tool uses the JDBC type LONG VARBINARY. The Sybase driver maps LONG VARBINARY to the native type IMAGE.

Although the type VARBINARY has fewer restrictions than IMAGE in Sybase, one cannot use it because it is limited to a size of 255 bytes, which is too small for typical serialized Java objects.

The specific restrictions on the IMAGE type are:

• We cannot use the IMAGE type in the WHERE clause of an SQL query. We can encounter this restriction whenever an enterprise bean contains an EJB-QL query that has a CMP type in the WHERE clause, which maps to the IMAGE type in the Sybase relational database (RDB).

• We cannot use IMAGE type in select queries marked DISTINCT. This situation arises in these user scenarios:

  • When the DISTINCT key word is specified in an EJB-QL select query having a Java type mapping to IMAGE.

  • When Enterprise beans have finder and ejbSelect() methods returning java.util. Set and have CMP types mapping to IMAGE.

To work around this restriction, edit the EJB mappings in the Rational Application Developer toolset and do either of the following:

• If you are sure that the serialized instance of the CMP type is never larger than 255 bytes, one can change the CMP type mapping from IMAGE or LONG VARBINARY to VARBINARY.

• Map the CMP type to multiple RDB fields through a composer. For example, if the CMP type is a Java object X with an int field and a string field, then map X to two RDB fields INTEGER and VARCHAR, using a composer. Refer to the Rational Application Developer documentation for more information about using composers.

 

A ClassCastException exception occurs when running container-managed

persistence 1.1 beans

If you created your EJB application using Rational Application Developer or WebSphere Studio Application Developer Integration Edition, V4.0.x , and the application contains container managed persistence (CMP) 1.1 beans with associations (relationships), you might receive a java.lang.ClassCastException exception when you run your application on WebSphere Application Server.

The cast operation generated by Rational Application Developer or WebSphere Studio Application Developer Integration Edition, V4.0.x does not use the javax.rmi.PortableRemoteObject.narrow(...) object to convert the remote object to the remote interface of CMP beans in the XToYLink.java (or YToXLink.java) class where X and Y are CMP 1.1 beans.

Recommended response

1. Locate the following methods in all link classes, for example, XToYLink.java and YToXLink.javawhere X and Y are CMP 1.1 beans

   public void secondaryAddElementCounterLinkOf(javax.ejb.EJBObject anEJB)
   public void secondaryRemoveElementCounterLinkOf(javax.ejb.EJBObject anEJB) 
   public void secondarySetCounterLinkOf(javax.ejb.EJBObject anEJB)
   

2. Add the javax.rmi.PortableRemoteObject.narrow(...) object to convert the remote object to the remote interface of CMP beans.

For example, change the following original method

public void secondaryAddElementCounterLinkOf(javax.ejb.EJBObject anEJB) throws java.rmi.RemoteException {
        if (anEJB != null) 
               ((X) anEJB).secondaryAddY((Y) getEntityContext().getEJBObject()); 

to:

public void secondaryAddElementCounterLinkOf(javax.ejb.EJBObject anEJB) throws java.rmi.RemoteException {
        if (anEJB != null)
             ((X) anEJB).secondaryAddY((Y)
javax.rmi.PortableRemoteObject.narrow(getEntityContext().getEJBObject(), Y.class)); 

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