To simplify matters we assume that:

1. A doctor can have multiple patients.
2. A patient can be seen by multiple doctors.
3. A patient can have more than one illness.
4. Only one patient can have a certain illness.
5. Only one doctor can cure any one illness.

/**
* CMP Bean utilizing XDoclet tags to represent a
* Doctor entity.
*
* @ejb.bean
* name="Doctor"
* type="CMP"
* local-jndi-name="Doctor"
* primkey-field="doctorId"
* view-type="local"
*
* @ejb.persistence
* table-name="doctor"
*
* @ejb.transaction
* type="Required"
*/

Method-level tags specify attributes such as a particular method's transactional configuration (if it should appear in the remote/local component interface), create methods, relationship attributes, etc. The following is an example from the Illness bean:

/**
* @ejb.interface-method
* @ejb.relation
* name="Doctor-Illness"
* role-name="Illness-Has-Doctor"
*
* @weblogic.column-map
* foreign-key-column="doctor_id"
* key-column="doctor_id"
*
*/
public abstract DoctorLocal getDoctor();

Container-Managed Relationships
One of the rather challenging tasks for XDoclet newcomers is establishing various container-managed relationships among CMP entity beans via the XDoclet tags. XDoclet handles relationships with the @ejb.relation tag and @weblogic.column-map for specifying the familiar <column-map> elements that must be listed in the weblogic-cmp-rdbms-jar.xml file. Let's look at an example from PatientBean.java:

/**
* @ejb.interface-method
* @ejb.relation
* name="Doctors-Patients"
* role-name="Patients-Have-Doctors"
*
* @weblogic.relation
* join-table-name="doctor_patient_link"
*
* @weblogic.column-map
* foreign-key-column="patient_id_fk"
* key-column="patient_id"
*
*/
public abstract Collection getDoctors();

Here we are specifying a many-to-many relationship between the Doctor and the Patient beans. The name and role-name attributes will be used to generate the necessary elements in the ejb-jar.xml file. The WebLogic-specific tags specify a common join table for the relationship as well as the <column-map> elements that will be used in the generated weblogic-cmp-rdbms-jar.xml file. A bidirectional relationship is implied here due to the corresponding XDoclet relationship tags in DoctorBean.java. To demonstrate how a windirectional relationship is described, let's look at PatientBean,java.

/**
* @ejb.interface-method
* @ejb.relation
* name="Patients-Illness"
* role-name="Patient-Has-Illness"
* target-ejb="Illness"
* target-role-name="Illness-Has-Patient"
* target-cascade-delete="yes"
*
* @weblogic.target-column-map
* foreign-key-column="patient_id"
* key-column="patient_id"
*/
public abstract Collection getIllnesses();

Here we are specifying a unidirectional relationship between the Patient and Illness beans. The target-ejb, target-role-name, and target-cascade-delete are used to specify the other side of the unidrectional relationship. XDoclet tags describing this particular relationship are not included in the corresponding Illness bean, since we are explicitly specifying the related entity from the Patient bean. In a unidrectional relationship, the @weblogic.target-column-map tag is used to specify the related bean's <column-map> elements.

Other WebLogic-Specific XDoclet tags
XDoclet supports both WebLogic 6.1 and 7.0 deployment descriptor settings. Instead of describing various WebLogic-specific characterstics for EJBs explicitly in the weblogic-ejb-jar.xml and weblogic-cmp-rdbms-jar.xml files, you can express them using XDoclet tags in the centralized EJB bean file. This eliminates the need to create these XML files manually.

Following is an example of how to configure WebLogic to autoincrement an entity bean's primary key, set the concurrency strategy element to ReadOnly, and specify that the WebLogic server is not required to call ejbLoad() upon each new transaction:

/**
* @weblogic.cache
* concurrency-strategy="ReadOnly"
* read-timeout-seconds="5"
*
* @weblogic.persistence
* db-is-shared="False"
*
* @weblogic.automatic-key-generation
* generator-type="ORACLE"
* generator-name="doctor_seq"
* key-cache-size="10"
*/

XDoclet provides many other WebLogic tags that allow the developer to conveniently configure features such as clustering, field groups, and relationship caching in a single bean file via Javadoc comments. Consult the XDoclet documentation for more information on these specific tags as well as other features provided by XDoclet. Utilizing the powerful capabilities of XDoclet with BEA WebLogic Server defintitely facilitates the development of EJBs.

References