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92 Chapter 8. Developing Entity Beans
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cmp-version
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1.x
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/cmp-version
9
8
cmp-field
9
8
field-name
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fieldOne
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/field-name
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8
/cmp-field
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8
cmp-field
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8
field-name
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fieldTwo
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/field-name
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8
/cmp-field
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With
container-managed persistence
the programmer need not develop the code for access-
ing the data in the relational database; this code is included in the container itself (generated by the
platform tools). However, for the EJB platform to know how to access the database and which data to
read and write in the database, two types of information must be provided with the bean:
•
First, the container must know which database to access and how to access it. To do this, the only
required information is the name of the DataSource that will be used to get the JDBC connection.
For container-managed persistence, only one DataSource per bean should be used.
•
Then, it is necessary to know the mapping of the bean fields to the underlying database (which table,
which column). For CMP 1.1 or CMP 2.0, this mapping is specified by the deployer in the JOnAS-
specific deployment descriptor. Note that for CMP 2.0, this mapping may be entirely generated by
JOnAS.
The EJB specification does not specify how this information should be provided to the EJB platform
by the bean deployer. Therefore, what is described in the remainder of this section is specific to JOnAS .
For CMP 1.1, the bean deployer is responsible for defining the mapping of the bean fields to the
database table columns. The name of the DataSource can be set at deployment time, since it depends
on the EJB platform configuration. This database configuration information is defined in the JOnAS-
specific deployment descriptor via the
jdbc-mapping
element. The following example defines the
mapping for a CMP 1.1 Entity Bean:
8
jdbc-mapping
9
8
jndi-name
9
jdbc_1
8
/jndi-name
9
8
jdbc-table-name
9
accountsample
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/jdbc-table-name
9
8
cmp-field-jdbc-mapping
9
8
field-name
9
mAccno
8
/field-name
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8
jdbc-field-name
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accno
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/jdbc-field-name
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8
/cmp-field-jdbc-mapping
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8
cmp-field-jdbc-mapping
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8
field-name
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mCustomer
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/field-name
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8
jdbc-field-name
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customer
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/jdbc-field-name
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8
/cmp-field-jdbc-mapping
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8
cmp-field-jdbc-mapping
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8
field-name
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mBalance
8
/field-name
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8
jdbc-field-name
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balance
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/jdbc-field-name
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8
/cmp-field-jdbc-mapping
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8
/jdbc-mapping
9
jdbc_1
is the JNDI name of the DataSource object identifying the database.
accountsample
is the
name of the table used to store the bean instances in the database.
mAccno
,
mCustomer
, and
mBalance
are the names of the container-managed fields of the bean to be stored in the
accno
,
customer
, and
balance
columns of the
accountsample
table. This example applies to
container-managed persistence
. For
bean-managed persistence
, the database mapping
does not exist.
For a CMP 2.0 Entity Bean, only the
jndi-name
element of the
jdbc-mapping
is mandatory, since
the mapping may be generated automatically:
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jdbc-mapping
9
8
jndi-name
9
jdbc_1
8
/jndi-name
9