Declarative Control of an Entity Bean in .NET

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Declarative Control of an Entity Bean
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The behavior of the entity bean can be configured with the following tags: Q Q Q db-is-shared is-modified-method-name delay-updates-until-end-of-tx
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Q passivation-strategy Q read-write Q read-only You can change the behavior of ejbLoad () in a CMP entity bean by using the db-is-shared element in the deployment descriptor If you are sure that there is only one instance of the WebLogic server accessing a particular entity bean and there are no external applications modifying the underlying data, then calling ejbLoad() every time is unnecessary For this particular case you can set the value of db-is-shared to false (the default is true) in the deployment descriptor The effect is that ejbLoad () will only be called when this is the first reference from a client for the bean in question or when a transaction rolls back, with the result being a better performance Due to caching limitations, this will not work when WebLogic is configured to work in a cluster To change the behavior of the ejbStore () method, you can use two elements in the deployment descriptor The first one is is-modif ied-method-name The default behavior is that ejbStore () is called every time a commit occurs, independently of whether the data to be persisted has changed or not The trick here is for the developer to write a method that will return true if the data has changed or false if it has not This method is then used as the parameter for the is-modif ied-method-name tag, which will be called before ejbStore () to determine if it is necessary to persist the data This will work on both CMP and BMP, but make sure that you have fully tested the logic for using this method, as this is one of the places where developers typically get into trouble The data store does not get updated until a commit is done, so no intermediate results are available However, if you want other clients to be able to view intermediate results for transactions that are in progress, and your database can support a transaction isolation level of read uncommitted, you can make it happen by setting the value of the delay-updates-until-end-of-tx element to false What will happen is that ejbStore () will be called at the end of each method and the information sent over to the database, instead of waiting until the commit Note that the data sent at the end of each method is not committed to the database, just stored, until the transaction concludes There are also mechanisms to control the lifecycle of an entity bean For example, entity beans follow the normal lifecycle of passivation described in the previous chapter for stateful beans However, by setting the value of the passivation-strategy element in the deployment descriptor of the bean to transaction, it will passivate the instance of the bean at the completion of each transaction
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The default caching strategy of the container is called read-write This is basically where the data is brought into the cache at the beginning of each transaction with e j bLoad (), and sent to the data store using ejbStore () at the end of each transaction This behavior can be modified as described earlier WebLogic has another cache strategy available, which is called read-only This strategy will not execute the ejbStore () method, and will execute the ejbLoad () method at the beginning and at regular intervals thereafter The intervals are defined by the read-timeout-seconds element Note that the transaction attribute for a bean using a read-only caching strategy has to be set to NotSupported WebLogic does not implement read-mostly caching; this is defined as read-only exported to most machines However, the same effect can be achieved manually with a combination of read-write and read-only EJBs You start with a read-only bean that reads the data at the specified intervals Then you define a separate read-write bean that models the same data as the read-only bean, which gets updated as required Enough theory, let's try out entity bean development
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