web server - Borland Technical Publications

Container-Managed Persistence in Borland Enterprise Server
java.util.Collection OrderItemHome.findByOrder(Order order);
This method returns all OrderItems associated with a particular Order. The deployment
descriptor entry for its where clause would be:
findByOrder(Order order)
order_id = :order[ejb/orders]
To produce this where clause, the Container substitutes the primary key of the Order
object for the string :order[ejb/orders]. The string between the brackets (in this
example, ejb/orders) must be the corresponding to the home of the
parameter type. In this example, ejb/orders corresponds to an pointing to
OrderHome.
When you use an EJBObject as a compound type (using the dot notation), you are
actually accessing the underlying get method for the field in the definition. For
example, the following in the definition:
order_id = :order.orderId
calls the getOrderId() method on the order EJBObject and uses the result of the call in
the selection criterion.
Specifying relationships between entities
Relational databases (RDBMS) permit records in one table to be associated with
records in another table. The RDBMS accomplishes this using foreign keys; that is, a
record in one table maintains a field (or column) that is a foreign key or reference to
(usually) the primary key of a related record in another table. You can map these same
references among entity beans.
For the CMP engine to map references among entity beans, you use an
entry in the deployment descriptor. The maps field names to their
corresponding entities. The CMP engine uses this information in the deployment
descriptor to locate the field's associated entity. (Refer to the pigs example for an
illustration of the entry.)
Any container-managed persistence field can correspond to a foreign key field in the
corresponding table. When you look at the entity bean code, these foreign key CMP
fields appear as object references.
For example, suppose you have two database tables, an address table and a country
table. The address table contains a reference to the country table. The SQL create
statements for these tables might look as shown below.
create table address (
addr_id number(10),
addr_street1 varchar2(40),
addr_street2 varchar(40),
addr_city varchar(30),
addr_state varchar(20),
addr_zip varchar(10),
addr_co_id number(4) * foreign key *
);
create table country (
co_id
number(4),
co_name varchar2(50),
co_exchange number(8, 2),
co_currency varchar2(10)
);
Note that the address table contains the field addr_co_id, which is a foreign key
referencing the country table's primary key field, co_id.
118 BES Developer’s Guide