web server - Borland Technical Publications

Container-Managed Persistence in Borland Enterprise Server
Note
or:
where a = b
a = b
The Container converts a = b to the same where clause, where a = b. However, it leaves
unmodified an empty string defined as “” .
The empty string makes it easy to specify the findAll() method. When you specify just
an empty string, the Container construes that to mean the following:
select [values] from [table];
Such a select statement would return all values from a particular table.
Parameter substitution
Parameter substitution is an important part of the where clause. The Borland EJB
Container does parameter substitution wherever it finds the standard SQL substitution
prefix colon (:). Each parameter for substitution corresponds to a name of a parameter
in the finder specification found in the XML descriptor.
For example, in the XML deployment descriptor, you might define the following finder
method which takes a parameter balance (note that balance is preceded by a colon):
findAccountsLargerThan(float balance)
balance > :balance
The Container composes a SQL select statement whose where clause is:
balance > ?
Note that the :balance parameter in the deployment descriptor becomes a question
mark (?) in the equivalent SQL statement. When invoked, the Container substitutes the
value of the parameter :balance for the ? in the where clause.
Compound parameters
The Container also supports compound parameters; that is, the name of a table
followed by a column within the table. For this, it uses the standard dot (.) syntax,
where the table name is separated from the column name by a dot. These parameters
are also preceded by a colon.
For example, the following finder method has the compound parameters :address.city
and :address.state:
findByCity(Address address)
city = :address.city AND state = :address.state
The where clause uses the city and state fields of the address compound object to
select particular records. The underlying Address object could have Java Beans-style
getter methods that correspond to the attributes city and state. Or, alternatively, it
could have public fields that correspond to the attributes.
Entity beans as parameters
An entity bean can also serve as a parameter in a finder method. You can use an entity
bean as a compound type. To do so, you must tell the CMP engine which field to use
from the entity bean's passed reference to the SQL query. If you do not use the entity
bean as a compound type, then the Container substitutes the bean's primary key in the
where clause.
For example, suppose you have a set of OrderItems entity beans associated with an
Order entity object. You might have the following finder method:
Chapter 14: Entity Beans and CMP 1.1 in Borland Enterprise Server 117