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Oracle® Containers for J2EE Orion CMP Developer's Guide
10g Release 3 (10.1.3) B19177-01 |
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Oracle® Containers for J2EE Orion CMP Developer's Guide
10g Release 3 (10.1.3) B19177-01 |
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Each entity bean instance has a primary key that uniquely identifies it from other instances. You must declare the primary key (or the fields contained within a complex primary key) as a container-managed persistent field in the deployment descriptor.
This section describes the following aspects of the primary key configurations:
All fields within the primary key are restricted to either primitive, serializable, or types that can be mapped to SQL types. You can define your primary key in one of the following ways:
Define the type of the primary key to be a well-known type. The type is defined in the <prim-key-class> element in the deployment descriptor. The data field that is identified as the persistent primary key is identified in the <primkey-field> element in the deployment descriptor. The primary key variable that is declared within the bean class must be declared as public.
The advanced option of defining the primary key is to define its type as a serializable object within a serializable <NAME>PK class. This class is declared in the <prim-key-class> element in the deployment descriptor. See "Configuring Primary Key Class" for more information.
Specify an automatically generated primary key: if you specify a java.lang.Object as the primary key class type in <prim-key-class>, but do not specify the primary key name in <primkey-field>, then the primary key is automatically generated by the container. See "Configuring Automatic Primary Key Generation" for more information.
Example 5-1 Defining a Primary Key of a Well-Known Type Within the Deployment Descriptor
For a simple CMP, you can define your primary key to be a well-known type by defining the data type of the primary key within the deployment descriptor. Example 5-1 shows how to define the primary key (employee number) as a java.lang.Integer:
<enterprise-beans> <entity> <display-name>Employee</display-name> <ejb-name>EmployeeBean</ejb-name> <local-home>employee.EmployeeLocalHome</local-home> <local>employee.EmployeeLocal</local> <ejb-class>employee.EmployeeBean</ejb-class> <persistence-type>Container</persistence-type> <prim-key-class>java.lang.Integer</prim-key-class> <reentrant>False</reentrant> <cmp-version>2.x</cmp-version> <abstract-schema-name>Employee</abstract-schema-name> <cmp-field><field-name>empNumber</field-name></cmp-field> <cmp-field><field-name>empName</field-name></cmp-field> <cmp-field><field-name>salary</field-name></cmp-field> <primkey-field>empNumber</primkey-field> </entity> ... </enterprise-beans>
Once defined, the container creates a column in the entity bean table for the primary key and maps the primary key defined in the deployment descriptor to this column.
Within the orion-ejb-jar.xml file, the primary key is mapped to the underlying database persistence storage by mapping the container-managed persistent field or primary key field defined in the ejb-jar.xml file to the database column name. In the following orion-ejb-jar.xml fragment, the EmpBean persistence storage is defined as the EMP table in the database that is defined in the jdbc/OracleDS data source. Following the <entity-deployment> element definition (see Table A-1, "Attributes of the <entity-deployment> Element"), the primary key, empNumber, is mapped to the EMPNUMBER column in the EMP table, and the empName and salary persistent fields are mapped to EMPNAME and SALARY columns respectively in the EMP table:
<entity-deployment name="EmpBean" ...table="EMP" data-source="jdbc/OracleDS"...> <primkey-mapping> <cmp-field-mapping name="empNumber" persistence-name="EMPNUMBER" /> </primkey-mapping> <cmp-field-mapping name="empName" persistence-name="EMPNAME" /> <cmp-field-mapping name="salary" persistence-name="SALARY" /> ...
If your primary key is more complex than a simple data type, your primary key must be a class that is serializable of the name <NAME>PK. You define the primary key class within the <prim-key-class> element in the deployment descriptor.
The primary key variables must adhere to the following:
Be defined within a <cmp-field><field-name> element in the deployment descriptor. This enables the container to manage the primary key fields.
Be declared within the bean class as public and restricted to be either primitive, serializable, or types that can be mapped to SQL types.
The names of the variables that make up the primary key must be the same in both the <cmp-field><field-name> elements and in the primary key class.
Within the primary key class, you implement a constructor for creating a primary key instance. Once the primary key class is defined in this manner, the container manages the class.
Example 5-2 Defining the Primary Key Class
Example 5-2 places the employee number within a primary key class.
package employee;
public class EmployeePK implements java.io.Serializable {
public Integer empNumber;
public EmployeePK() {
this.empNumber = null;
}
public EmployeePK(Integer newEmpNumber) {
this.empNumber = newEmpNumber;
}
}
Example 5-3 Declaring the Primary Key Class in the Deployment Descriptor
The primary key class is declared in the deployment descriptor within the <prim-key-class> element, and each of its variables are declared within a <cmp-field><field-name> element, as Example 5-3 shows:
<enterprise-beans> <entity> <description>no description</description> <display-name>EmployeeBean</display-name> <ejb-name>EmployeeBean</ejb-name> <local-home>employee.EmployeeLocalHome</local-home> <local>employee.EmployeeLocal</local> <ejb-class>employee.EmployeeBean</ejb-class> <persistence-type>Container</persistence-type> <prim-key-class>employee.EmployeePK</prim-key-class> <reentrant>False</reentrant> <cmp-version>2.x</cmp-version> <abstract-schema-name>Employee</abstract-schema-name> <cmp-field><field-name>empNumber</field-name></cmp-field> <cmp-field><field-name>empName</field-name></cmp-field> <cmp-field><field-name>salary</field-name></cmp-field> </entity> ... </enterprise-beans>
Once you define the primary key, the container creates a column in the entity bean table for the primary key and maps the primary key class declared in the deployment descriptor to this column.
The persistent fields are mapped in the orion-ejb-jar.xml in the same manner as described in the "Configuring Primary Key" section. With a complex primary key, the mapping contains more than a single field; thus, the <cmp-field-mapping> element of the <primkey-mapping> element contains another <fields> subelement. Every field of the primary key is defined in a separate <cmp-field-mapping> element within the <fields> element, similar to the following:
<primkey-mapping> <cmp-field-mapping> <fields> <cmp-field-mapping name="empNumber" persistence-name="EMPNUMBER" /> </fields> </cmp-field-mapping> </primkey-mapping>
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Note: If you have a complex primary key that contains a foreign key, you need to apply a special mapping. See "Configuring Foreign Key in a Composite Primary Key" for more information. |
In the EJB 2.0 specification, the primary key for an entity bean must be initialized within the ejbCreate method. However, in this method you cannot set any relationship that this bean has to another bean. The earliest when you can set this relationship in a foreign key is in the ejbPostCreate method.
That said, if you have a foreign key within a composite primary key, you face the following problem: you must set all fields within the composite primary key in the ejbCreate method, but you cannot set the foreign key in this method.
The following hypothetical scenario models the way around this problem: an order can contain one or more items; the order bean has many items in it; each item belongs to an order. The primary key for the item is a composite primary key consisting of the item identifier and the order identifier. The order identifier is a foreign key that points to the order.
You would have to modify the deployment descriptors and bean implementation to add a placeholder persistent field that mimics the actual foreign key field. This field is set during the ejbCreate method. However, both the placeholder persistent field and the foreign key point to the same database column. The actual foreign key is updated during the ejbPostCreate method.
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Note: Modify theejb-jar.xml file with the placeholder persistent field and the foreign key. Deploy the application with <autocreate-tables> element in the orion-application.xml file set to false to automatically generate the orion-ejb-jar.xml file, without creating any tables. Then modify the orion-ejb-jar.xml file to point to the correct database columns, set <autocreate-tables> element to true, and redeploy.
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Example 5-4 Modifying the Deployment Descriptor and the Bean Code to Accommodate a Foreign Key Within a Primary Key
Example 5-4 demonstrates how to modify both deployment descriptors and the bean implementation.
In the order scenario, each order contains one or more items. The OrderBean represents the order, and the OrderItemBean represents the items in the order. Each item has a primary key that consists of the item number and the order number to which it belongs. Thus, the primary key for the item contains a foreign key that points to an order bean.
To adjust for a composite primary key, modify the ejb-jar.xml file in the following way:
Define a persistent field in the primary key as a placeholder for the foreign key. This placeholder should be used in the composite primary key class definition.
In the Example 5-4, an orderId persistent field is defined in a <cmp-field> element. The orderId and itemId persistent fields are used to identify the composite primary key in the OrderItemPK.java.
Define the foreign key outside the primary key definition in its own <cmr-field> element in the <relationships> section.
In the Example 5-4, the belongToOrder foreign key is defined in a <cmr-field> element for the OrderItemBean, defining the relationship from the item to the order.
<entity> <ejb-name>OrderItemBean</ejb-name> <local-home>OrderItemLocalHome</local-home> <local>OrderItemLocal</local> <ejb-class>OrderItemBean</ejb-class> ... <cmp-field><field-name>itemId</field-name></cmp-field> <cmp-field><field-name>orderId</field-name></cmp-field> <cmp-field><field-name>price</field-name></cmp-field> <prim-key-class>OrderItemPK</prim-key-class> ... </entity> <relationships> <ejb-relation> <ejb-relation-name>Order-OrderItem</ejb-relation-name> <ejb-relationship-role> <ejb-relationship-role-name> Order-Has-OrderItems </ejb-relationship-role-name> <multiplicity>One</multiplicity> <relationship-role-source> <ejb-name>OrderBean</ejb-name> </relationship-role-source> <cmr-field> <cmr-field-name>items</cmr-field-name> <cmr-field-type>java.util.Collection</cmr-field-type> </cmr-field> </ejb-relationship-role> <ejb-relationship-role> <ejb-relationship-role-name> OrderItems-from-Order </ejb-relationship-role-name> <multiplicity>Many</multiplicity> <cascade-delete/> <relationship-role-source> <ejb-name>OrderItemBean</ejb-name> </relationship-role-source> <cmr-field> <cmr-field-name>belongToOrder</cmr-field-name> </cmr-field> </ejb-relationship-role> ...
The OrderItemPK.java class defines the contents of the complex primary key, as follows:
public class OrderItemPK implements java.io.Serializable {
public Integer itemID;
public Integer orderID;
public OrderItemPK() {
this.itemId = null;
this.orderId = null;
}
public OrderItemPK(Integer newItemId, Integer newOrderId) {
this.itemId = newItemId;
this.orderId = newOrderId;
}
public boolean equals(Object o) {
if (o instanceof OrderItemPK) {
OrderItemPK pk = (OrderItemPK) o;
if (pk.itemId.intValue() == itemId.intValue() &&
pk.orderId.intValue() == orderId.intValue()) {
return true;
}
}
return false;
}
public int hashCode() {
return itemId.hashCode() * orderId.hashCode();
}
}
If you consider the automatically created database tables sufficient, you do not need to modify the orion-ejb-jar.xml file. However, if you need to map to existing database tables, then you modify the orion-ejb-jar.xml file to point to these tables (see "Configuring Explicit Mapping of Relationship Fields to the Database" for more information).
After the automatic generation of the orion-ejb-jar.xml file, copy it into your development directory. The database column names are defined in the persistence-name attributes in each of the persistent and relationship field name mappings. Ensure that the persistence-name attributes for both the placeholder persistent field and foreign key are the same.
The following is the orion-ejb-jar.xml file for the Order/OrderItem example:
<entity-deployment name="OrderItemBean" table="ORDER_ITEM"> <primkey-mapping> <cmp-field-mapping name="itemId" persistence-name="Item_ID" /> <cmp-field-mapping name="orderId" persistence-name="Order_ID" /> </primkey-mapping> <cmp-field-mapping name="price" persistence-name="Price" /> <cmp-field-mapping name="belongToOrder"> <entity-ref home="OrderBean"> <cmp-field-mapping name="belongToOrder" persistence-name="Order_ID" /> </entity-ref> </cmp-field-mapping> </entity-deployment> <entity-deployment name="OrderBean" table="ORDER"> <primkey-mapping> <cmp-field-mapping name="orderId" persistence-name="Order_ID" /> </primkey-mapping> <cmp-field-mapping name="orderDesc" persistence-name="Order_Description" /> <cmp-field-mapping name="items"> <collection-mapping table="ORDER_ITEM"> <primkey-mapping> <cmp-field-mapping name="OrderBean_orderId"> <entity-ref home="OrderBean"> <cmp-field-mapping name="OrderBean_orderId"> </entity-ref> </cmp-field-mapping> </primkey-mapping> <value-mapping type="OrderItemLocal"> <cmp-field-mapping name="OrderItemBean_itemId"> <entity-ref home="OrderItemBean"> <cmp-field-mapping name="OrderItemBean_itemId"> <cmp-field-mapping name="OrderItemBean_itemId"> </fields> </cmp-field-mapping> </entity-ref> </cmp-field-mapping> </value-mapping> </collection-mapping> </cmp-field-mapping> </entity-deployment>
The following takes place in the <entity-deployment> (see Table A-1, "Attributes of the <entity-deployment> Element") section for the OrderItemBean of the orion-ejb-jar.xml file for the Order/OrderItem example:
The table is defined in the table attribute, which is ORDER_ITEM in this example.
The column name for the itemId is defined in the persistence-name attribute as Item_ID.
The column name for the placeholder persistent field, orderId, is defined in the persistence-name attribute as Order_ID.
The foreign key, belongToOrder, is mapped to the database column, Order_ID, which is the same column as the placeholder persistent field, orderId.
Both the foreign key (belongToOrder), and the placeholder persistent field (orderId) must point to the same database column.
Finally, you must update the bean implementation to work with both the placeholder persistent field and the foreign key, as follows:
In the ejbCreate method, do the following:
Create the placeholder persistent field that takes the place of the foreign key field.
Set a value in the placeholder persistent field in the ejbCreate method. This value is written out to the foreign key field in the database table.
In the ejbPostCreate method, set the foreign key to the value in the duplicate persistent field.
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Note: Since the foreign key is a part of a primary key, you can only set it once. |
In the Order/OrderItem example, the orderId persistent field is set in the ejbCreate method, whereas the belongToOrder relationship field is set in the ejbPostCreate method, as follows:
public OrderItemPK ejbCreate(OrderItem orderItem) throws CreateException {
setItemId(orderItem.getItemId());
setOrderId(orderItem.getOrderId());
setPrice(orderItem.getPrice());
return new OrderItemPK(orderItem.getItemId(),orderItem.getOrderId());
}
public void ejbPostCreate(OrderItem orderItem) throws CreateException {
// right after the bean has been created
try {
Context ctx = new InitialContext();
OrderLocalHome orderHome =
(OrderLocalHome)ctx.lookup("java:comp/env/OrderBean");
OrderLocal order = orderHome.findByPrimaryKey(orderItem.getOrderId());
setBelongToOrder(order);
}
catch(Exception e) {
e.printStackTrace();
throw new EJBException(e);
}
}
The following is the code for the OrderItem object that is passed into the ejbCreate and ejbPostCreate methods:
public class OrderItem implements java.io.Serializable {
private Integer itemId;
private Integer orderId;
private Double price;
public OrderItem(Integer itemId, Integer orderId, Double price) {
this.itemId = itemId;
this.orderId = orderId;
this.price = price;
}
public Integer getItemId() {
return itemId;
}
public void setItemId(Integer itemId) {
this.itemId = itemId;
}
public Integer getOrderId() {
return orderId;
}
public void setOrderId(Integer orderId) {
this.orderId = orderId;
}
public Double getPrice() {
return price;
}
public void setPrice(Double price) {
this.price = price;
}
public boolean equals(Object other) {
if (other instanceof OrderItem) {
OrderItem orderItem = (OrderItem)other;
if (itemId.equals(orderItem.getItemId()) &&
orderId.equals(orderItem.getOrderId()) &&
price.equals(orderItem.getPrice()) ) {
return true;
}
}
return false;
}
}
If you specify a java.lang.Object as the primary key class type in <prim-key-class> element of your deployment descriptor, but do not specify the primary key name in <primkey-field> element, then the primary key is automatically generated by the container, as follows:
<enterprise-beans> <entity> <display-name>Employee</display-name> <ejb-name>EmployeeBean</ejb-name> <local-home>employee.EmployeeLocalHome</local-home> <local>employee.EmployeeLocal</local> <ejb-class>employee.EmployeeBean</ejb-class> <persistence-type>Container</persistence-type> <prim-key-class>java.lang.Object</prim-key-class> <reentrant>False</reentrant> <cmp-version>2.x</cmp-version> <abstract-schema-name>Employee</abstract-schema-name> <cmp-field><field-name>empNumber</field-name></cmp-field> <cmp-field><field-name>empName</field-name></cmp-field> <cmp-field><field-name>salary</field-name></cmp-field> </entity> ... </enterprise-beans>
Once defined, the container creates a column called autoid in the entity bean table for the primary key of type LONG. The container uses random numbers for the primary key values. This is generated in the orion-ejb-jar.xml for the bean, as follows:
<primkey-mapping> <cmp-field-mapping name="auto_id" persistence-name="autoid"/> </primkey-mapping>
