Programming WebLogic Enterprise JavaBeans
The following sections describe the EJB 2.0 deployment descriptor elements found in the weblogic-cmp-jar.xml
file, the WebLogic-specific XML document type definitions (DTD) file. Use these definitions to create the WebLogic-specific weblogic-cmp-jar.xml
file that is part of your EJB deployment. Use this deployment descriptor file to specify container-managed-persistence (CMP) behavior.
For information on the EJB 1.1 deployment descriptor elements see Important Information for EJB 1.1 Users.
The weblogic-cmp-jar.xml
file defines deployment descriptors for entity EJBs that use WebLogic Server RDBMS-based persistence services. The EJB container uses a version of weblogic-cmp-jar.xml
that is different from the XML shipped with WebLogic Server Version 6.x.
You can continue to use the earlier weblogic-cmp-jar.xml
DTD for EJB 1.1 beans that you will deploy on the WebLogic Server Version 8.1. However, if you want to use any of the new CMP 2.0 features, you must use the new DTD described below.
The top-level element of the WebLogic Server 8.1 weblogic-cmp-jar.xml
consists of a weblogic-rdbms-jar
stanza:
description
weblogic-version
weblogic-rdbms-jar
weblogic-rdbms-bean
ejb-name
data-source-name
table-map
field-group
relationship-caching
weblogic-query
delay-database-insert-until
automatic-key-generation
check-exists-on-method
weblogic-rdbms-relation
relation-name
table-name
weblogic-relationship-role
order-database-operations
enable-batch-operations
create-default-dbms-tables
validate-db-schema-with
database-type
default-dbms-tables-ddl
compatibility
These changes were made to weblogic-cmp-jar.xml
in WebLogic Server 8.1:
This list of the elements in weblogic-cmp-jar.xml
includes all elements that were supported in any service pack of WebLogic Server 8.1. The previous section, Changes to weblogic-cmp-jar.xml in WebLogic Server 8.1 lists elements that were new, changed, or deprecated in Weblogic Server 8.1, or a subsequent service pack.
This element, introduced in WebLogic Server 8.1 SP02, is a backward compatibility flag. It is used to enable create and remove operations for an EJB that uses ReadOnly
concurrency.
Prior to version 8.1 SP2, these operations were allowed, although they had no transactional meaning. They have been disallowed so that more efficient code can be generated for ReadOnly
beans, and because using them is a bad practice.
<compatibility>
<allow-readonly-create-and-remove>
true
</allow-readonly-create-and-remove>
</compatibility>
The automatic-key-generation
element specifies how primary keys will be automatically generated. For more information about this feature, see Automatically Generating Primary Keys.
The following code samples show the automatic-key-generation
stanza for different primary key generation methods. For supported generation methods, see generator-type
Listing B-1 automatic-key-generation With generator-type=Oracle
<automatic-key-generation>
<generator-type>Oracle</generator-type>
<generator-name>test_sequence</generator-name>
<key-cache-size>10</key-cache-size>
</automatic-key-generation>
Listing B-2 automatic-key-generation With generator-type=SQL-SERVER
<automatic-key-generation>
<generator-type>SQL-SERVER</generator-type>
</automatic-key-generation>
Listing B-3 automatic-key-generation With generator-type=NamedSequenceTable
<automatic-key-generation>
<generator-type>NamedSequenceTable</generator-type>
<generator-name>MY_SEQUENCE_TABLE_NAME</generator-name>
<key-cache-size>100</key-cache-size>
</automatic-key-generation>
Specifies the cmr-field
and the group-name
in the related bean. If group-name
is not specified, the default group-name
(load all fields) is used. For more information, see group-name.
The caching-element
stanza can contain nested caching element stanzas, as in the example shown in relationship-caching.
For information about relationship caching, see Relationship Caching.
See relationship-caching:
The caching-name
element specifies the name of a relationship cache. For more information about relationship caching, see Relationship Caching.
See relationship-caching:
By default, the EJB container checks that a container-managed persistence (CMP) entity bean exists before any business method invoked on the bean completes. This means the container notifies an application as soon as any business method is invoked on a container-managed entity bean that has been removed.
To specify that the EJB container wait for transaction completion to perform the existence check, set check-exists-on-method
to False
. This results in high performance and still provides a sufficient level of checking for most applications.
The following example specifies that WebLogic Server notify the application that a business method has been invoked on a CMP entity bean that has been removed.
<check-exists-on-method>True</check-exists-on-method>
This name specifies the mapped field in the bean instance which should be populated with information from the database.
See field-map.
Specifies the name of a container-managed relationship field.
<cmr-field>stock options</cmr-field>
This element represents the mapping of a foreign key column in one table in the database to a corresponding primary key. The two columns may or may not be in the same table. The tables to which the columns belong are implicit from the context in which the column-map
element appears in the deployment descriptor.
Note: The key-column
element is not specified if the foreign-key-column
refers to a remote bean.
The XML
stanza can contain the elements shown here:
<column-map
<foreign-key-column>account-id</foreign-key-column>
<key-column>id</key-column>
</column-map>
The <compatibility>
stanza, introduced in WebLogic Server 8.1 SP02, contains elements that specify compatibility flags for all of the cmp beans described in the descriptor file.
<compatibility>
<serialize-byte-array-to-oracle-blob>
<allow-readonly-create-and-remove>
</compatibility>
The create-default-dbms-table
element performs two functions:
Use this element only for convenience during development phases. This is because the table schema in the DBMS CREATE
statement used are the EJB container's best approximation of the definition. A production environment typically requires more precise schema definition.
The following table describes how WebLogic Server handles automatic table creation, based on the value of create-default-dbms-tables
.
If TABLE CREATION
fails, the server throws a Table Not Found
error and the table must be created by hand.
See Automatic Table Creation (Development Only).
Note: Automatic Oracle SEQUENCE generation works only with servers running in development mode.
The following table describes how WebLogic Server handles automatic SEQUENCE generation, based on the value of create-default-dbms-tables
.
The EJB container takes no action with respect to SEQUENCE generation. This is the default value. |
|
The EJB container creates a SEQUENCE, and constructs its name by appending "_WL" to the value of the |
|
The EJB container creates a SEQUENCE, and constructs its name by appending "_WL" to the value of the If the SEQUENCE's increment value does not match the value of the key-cache-size element, the container alters the increment value to match the value of key-cache-size. |
|
The EJB container creates a SEQUENCE, and constructs its name by appending "_WL" to the value of the If the SEQUENCE's increment value does not match the value of the key-cache-size element, the container alters the increment value to match the value of key-cache-size. |
|
The EJB container creates a SEQUENCE, and constructs its name by appending "_WL" to the value of the If the SEQUENCE's increment value does not match the value of the key-cache-size element, the container alters the increment value to match the value of key-cache-size. |
For more information on automatic generation of an Oracle SEQUENCE, see Support for Oracle SEQUENCE.
The following example specifies the create-default-dbms-tables element.
<create-default-dbms-tables>CreateOnly</create-default-dbms-tables>
The database-type
element specifies the database used as the underlying dbms.
<database-type>POINTBASE</database-type>
Specifies the JDBC data source name to be used for database connectivity for this bean. For more information on datasources, see Programming WebLogic JDBC.
See table-name.
Allows an application to take advantage of a database's built-in support for cascade delete, and possibly improve performance. This functionality is supported only for:
If db-cascade-delete
is enabled in weblogic-cmp-rdbms-jar.xml
, you must
Note: If db-cascade-delete
is not specified, do not enable the database's cascade delete functionality, as this will produce incorrect results.
The following Oracle table definition will cause deletion all of the emp
rows if the owning dept
is deleted in the database.
CREATE TABLE dept
(deptno NUMBER(2) CONSTRAINT pk_dept PRIMARY KEY,
dname VARCHAR2(9) );
CREATE TABLE emp
(empno NUMBER(4) PRIMARY KEY,
ename VARCHAR2(10),
deptno NUMBER(2) CONSTRAINT fk_deptno
REFERENCES dept(deptno)
ON DELETE CASCADE );
</weblogic-relationship-role>
<db-cascade-delete/>
</weblogic-relationship-role>
The name of the database column to which the field should be mapped.
Note: dbms-column
is case maintaining, although not all database are case sensitive.
See field-map.
Specifies the type of the cmp-field
. the current field to a Blob or Clob in an Oracle database or a LongString or SybaseBinary in a Sybase database.
OracleBlob
—maps the field to an Oracle Blob.OracleClob
—maps the field to an Oracle Clob.LongString
—tells the container to use setCharacterStream
to write String data into the database. Some JDBC drivers have problems writing more than 4K of data using setString
.SybaseBinary
—tells the container to use setBytes
to write bytes into the binary column, because setBinaryStream
does not work with SybaseXADriver
.<field-map>
<cmp-field>photo</cmp-field>
<dbms-column>PICTURE</dbms-column>
<dbms_column-type>OracleBlob</dbms-column-type>
</field-map>
Specifies the DDL
file name to which the EJB container writes the table creation scripts.
Specifies when a new CMP bean is inserted into the database. The allowable values cause the following behavior:
ejbCreate
- perform database insert immediately after ejbCreate.
This setting yields better performance than ejbCreate
by avoiding an unnecessary store operation.ejbPostCreate
- perform insert immediately after ejbPostCreate.
This element has an effect only when order-database-operations is False
. By default, order-database-operations
is true
, which causes new beans to be inserted at the transaction commit time.
Delaying the database insert until after ejbPostCreate
is required when a cmr-field
is mapped to a foreign-key
column that does not allow null values. In this case, the cmr-field
must be set to a non-null value in ejbPostCreate
before the bean is inserted into the database.
For maximum flexibility, avoid creating related beans in your ejbPostCreate
method. If ejbPostCreate
creates related beans, and database constraints prevent related beans from referring to a bean that has not yet been created, it is not possible to database insert until after the method completion.
Note: cmr-field
s may not be set during ejbCreate
, before the primary key of the bean is known.
<delay-database-insert-until>ejbPostCreate</delay-database-insert-until>
The description
element provides text that describes the parent element.
<dscription>Contains a description of parent element</description>
The name that specifies an EJB as defined in the ejb-cmp-rdbms.xml
. This name must match the ejb-name
of a cmp entity bean contained in the ejb-jar.xml
.
See table-name.
This element, introduced in WebLogic Server 8.1, controls whether or not the EJB container allows batch database operations, including batch inserts, batch updates and batch deletes.
If this element is set to True
, the EJB delays database operations in a transaction until commit time.
Note: In WebLogic Server 8.1, this element replaces the functionality of the commit
setting, available in WebLogic Server 7.0, for the delay-database-insert-until element.
The following XML sample demonstrates use of the enable-batch-operations
element:
<enable-batch-operations>True</enable-batch-operations>
The field-group
element represents a subset of the cmp-fields and cmr-fields of a bean. Related fields in a bean can be put into groups that are faulted into memory together as a unit. A group can be associated with a finder or relationship, so that when a bean is loaded as the result of executing a finder or following a relationship, only the fields specified in the group are loaded.
A field may belong to multiple groups. In this case, the getXXX
method for the field faults in the first group that contains the field.
The XML
stanza can contain the elements shown here:
<weblogic-rdbms-bean>
<ejb-name>XXXBean</ejb-name>
<field-group>
<group-name>medical-data</group-name>
<cmp-field>insurance</cmp-field>
<cmr-field>doctors</cmr-fields>
</field-group>
</weblogic-rdbms-bean>
The field-map
element represents a mapping between a particular column in a database and a cmp-field
in the bean instance.
The optional group-name
element specifies a field group that is to be loaded when the getXXX
method for the cmp-field
is called and the EJB container needs to read the value from the DBMS because it is not in memory. If group-name
is omitted, the default group, which contains all cmp-field
s, is used when the cmp-field
is not explicitly listed in any field groups, otherwise a field group that contains the cmp-field
is chosen. Thus, developers should specify a group-name
if the cmp-field
is listed in multiple field groups or the container will pick one of the groups arbitrarily.
The dbms-column-type element is optional.
The XML
stanza can contain the elements shown here:
<field-map>
<cmp-field>....</cmp-field>
<dbms-column>...</dbms-column>
<dbms-column-type>...</dbms-column-type>
<group-name>...</group name>
</field-map>
The foreign-key-column
element represents a column of a foreign key in the database.
See column-map.
The foreign-key-table
element specifies the name of a DBMS table that contains a foreign key.
The generator-name
element is used to specify the name of the primary key generator.
Oracle
, and WebLogic Server is running in development mode, then the EJB container constructs the Oracle SEQUENCE name by appending "_WL" to the generator-name
as part of the container's automatic SEQUENCE generation feature.For more information on automatic Oracle SEQUENCE generation, see Support for Oracle SEQUENCE.
generator-type
element is Oracle
, and WebLogic Server is running in production mode, then the EJB container sets the name of the Oracle SEQUENCE to the value of generator-name
.generator-type
element is NamedSequenceTable
, then the generator-name
element would be the name of the SEQUENCE_TABLE
to be used.
The generator-type
element specifies the primary key generation method to use.
In addition, generator-type
is used in conjunction with automatic Oracle SEQUENCE generation. See Support for Oracle SEQUENCE.
Specifies the name of a field group.
See field-group.
Specifies whether updates made during the current transaction must be reflected in the result of a query. If this element is set to True
, the container will flush all changes made by the current transaction to disk before executing the query. A value of False
provides best performance.
<weblogic-query>
<query-method>
<method-name>findBigAccounts</method_name>
<method-params>
<method-param>double</method-param>
</method-params>
</query-method>
<weblogic-ql>WHERE BALANCE>10000 ORDERBY NAME</weblogic-ql>
<include-updates>True</include-updates>
</weblogic-query>
Specifies a locking or processing order for instances of a particular EJB. This element can be used to prevent deadlocks in an application that would otherwise experience deadlocks. instance-lock-order
is used whenever database operations (update, for example) that apply to multiple instances of the same EJB are performed by the container. It specifies an order for operations that can cause a database lock to be acquired for a bean instance.
For example, instance-lock-order
could be used to specify the order in which the EJB container calls ejbStore
for instances of a particular EJB that uses database concurrency; ejbStore
may acquire an exclusive lock when a database update is done. instance-lock-order
also controls the order in which beans using optimistic concurrency are locked when optimistic checking is performed.
AccessOrder
—The container will process beans so that locks are acquired (or upgraded) in the order in which the application originally accessed the beans during the transaction. This is the recommended value when all transactions in the system access instances of the bean, and ultimately rows in a database table, in the same order.instance-lock-order
—ValueOrder
-Beans are processed in order based on the value of their primary key. ValueOrder
should be specified to avoid deadlocks when concurrent transactions access instances of the same EJB in different orders.Note: The EJB's primary key class is not required to implement the java.lang.Comparable
interface when ValueOrder
is specified, although this will result in a total ordering. Beans are ordered partially using the hash code value of the primary key when the primary key does not implement java.lang.Comparabl
e.
<instance-lock-order>ValueOrder</instance-lock-order>
Specifies the optional size of the primary key cache available in the automatic primary key generation feature. In addition, the EJB container uses this value to calculate the increment value for an Oracle SEQUENCE when automatic SEQUENCE generation is enabled. See Support for Oracle SEQUENCE.
If generator-type is
Oracle
—key-cache-size
must match the Oracle SEQUENCE INCREMENT value. If there is a mismatch between this value and the Oracle SEQUENCE INCREMENT value, then there will likely be duplicate key problems.NamedSequenceTable
—key-cache-size
specifies how many keys the container will fetch in a single DBMS callkey-cache-size
is ignored.
The key-column
element represents a column of a primary key in the database.
See column-map.
Use this flag to specify the database locking order of an entity bean when a transaction involves multiple beans and exclusive concurrency. The bean with lowest number is locked first.
This flag should only be used to prevent a deadlock situation and, currently, only applies when a transaction performs cascade deletes.This flag is only used for cascade delete currently.
The XML
stanza can contain the elements shown here:
<lock-order>1</lock-order>
<!ELEMENT lock-order (PCDATA)>
max-elements
specifies the maximum number of elements that should be returned by a multi-valued query. This element is similar to the maxRows
feature in JDBC.
The XML
stanza can contain the elements shown here:
<max-elements>100</max-elements>
<!ELEMENT max-element (PCDATA)>
The method-name
element specifies the name of a finder or ejbSelect
method.
Note: The `*' character may not be used as a wildcard.
See weblogic-query.
The method-param
element contains the fully qualified Java type name of a method parameter.
<method-param>java.lang.String</method-param>
The method-params
element contains an ordered list of the fully-qualified Java type names of the method parameters.
See weblogic-query.
The optimistic-column
element denotes a database column that contains a version or timestamp value used to implement optimistic concurrency. For more information on optimistic concurrency, see Choosing a Concurrency Strategy.
Note: Although not all databases are case sensitive, this element is case maintaining.
The following sample XML shows the use of the optimistic-column
element.
<optimistic-column>ROW_VERSION</optimistic-column>
where ROW_VERSION
is the name of a database column that contains the value used for concurrency checking.
This element, introduced in WebLogic Server 8.1, determines whether the EJB container delays all database operations in a transaction until commit time, automatically sorts the database dependency between the operations, and sends these operations to the database in such a way to avoid any database constraint errors.
If enable-batch-operations is set to True
, the container automatically sets order-database-operations
to True
. To turn off order-database-operations
, set both order-database-operations
and enable-batch-operations
to False
.
See also enable-batch-operations and delay-database-insert-until.
The following sample XML demonstrates the use of the order-database-operations
element.
<order-database-operations>True</order-database-operations>
The primary-key-table
element specifies the name of a DBMS table that contains a primary key. For more information about primary keys, see Using Primary Keys.
Note: Although not all databases are case sensitive, this element is case maintaining.
For examples, see relationship-role-map and Mapping a Bean on Primary Key Side of a Relationship to Multiple Tables.
Specifies the method that is associated with a weblogic-query
. It also uses the same format as the ejb-jar.xml
descriptor.
See weblogic-query.
The relation-name
element specifies the name of a relation.
For more information about container-managed relationships, see Using Container-Managed Relationships (CMRs).
The XML
stanza can contain the elements shown here:
<weblogic-rdbms-jar>
<weblogic-rdbms-relation>
<relation-name>stocks-holders</relation-name>
<table-name>stocks</table-name>
</weblogic-rdbms-relation>
</weblogic-rdbms-jar>
The relation-caching
element specifies relationship caching. For more information about relationship caching, see Relationship Caching.
The XML
stanza can contain the elements shown here:
<relationship-caching>
<caching-name>cacheMoreBeans</caching-name>
<caching-element>
<cmr-field>accounts<</cmr-field>
<group-name>acct_group</group-name>
<caching-element>
<cmr-field>address</cmr-field>
<group-name>addr_group</group-name>
</caching-element>
</caching-element>
<caching-element>
<cmr-field>phone</cmr-field>
<group-name>phone_group</group-name>
</caching-element>
</relationship-caching>
The relationship-role-map
element specifies foreign key column to key column mapping for beans involved in a relationship.
A CMP bean that is involved in a relationship may be mapped to multiple DBMS tables (see the table-map element for more details). If the bean on the foreign key side of a one-to-one or one-to-many relationship is mapped to multiple tables, then the name of the table containing the foreign-key columns must be specified using the foreign-key-table
element.
Conversely, if the bean on the primary key side of a one-to-one or one-to-many relationship or a bean participating in a m-n relationship is mapped to multiple tables, then the name of the table containing the primary key must be specified using the primary-key-table
element.
If neither of the beans in a relationship is mapped to multiple tables, then the foreign-key-table
and primary-key-table
elements can be omitted because the tables being used are implicit.
For more information about container-managed relationships, see Using Container-Managed Relationships (CMRs).
The bean on the foreign-key side of a one-to-one relationship, Fk_Bean
, is mapped to multiple tables. The table that holds the foreign key columns must be specified in the foreign-key-table
element.
Fk_Bean
is mapped to two tables: Fk_BeanTable_1
and Fk_BeanTable_2
. The foreign key columns for the relationship are located in table Fk_BeanTable_2
. The foreign key columns are named Fk_column_1
and Fk_column_2
. The bean on the primary key side, Pk_Bean
, is mapped to a single table with primary key columns Pk_table_pkColumn_1
and Pk_table_pkColumn_2
:
<relationship-role-map
<foreign-key-table>Fk_BeanTable_2</foreign-key-table>
<column-map>
<foreign-key-column>Fk_column_1</foreign-key-column>
<key-column>Pk_table_pkColumn_1</key-column>
</column-map>
<column-map>
<foreign-key-column>Fk_column_2</foreign-key-column>
<key-column>Pk_table_pkColumn_2</key-column>
</column-map>
</relationship-role-map>
The foreign-key-table
element must be specified so that the container can know which table contains the foreign key columns.
The bean on the primary key side of a one-to-one relationship, Pk_bean
, is mapped to multiple tables, but the bean on the foreign key side of the relationship, Fk_Bean
, is mapped to one table, Fk_BeanTable
. The foreign key columns are named Fk_column_1
and Fk_column_2
.
Pk_BeanTable_1
with primary key columns Pk_table1_pkColumn_1
and Pk_table1_pkColumn_2
and Pk_BeanTable_2
with primary key columns Pk_table2_pkColumn_1
and Pk_table2_pkColumn_2
. <relationship-role-map>
<primary-key-table>Pk_BeanTable_1</primary-key-table>
<column-map>
<foreign-key-column>Fk_column_1</foreign-key-column>
<key-column>Pk_table1_pkColumn_1</key-column>
</column-map>
<column-map>
<foreign-key-column>Fk_column_2</foreign-key-column>
<key-column>Pk_table1_pkColumn_2</key-column>
</column-map>
</relationship-role-map>
The relationship-role-name
element specifies the name of a relationship role.
For more information about container-managed relationships, see Using Container-Managed Relationships (CMRs).
See the examples for weblogic-relationship-role.
This element, introduced in WebLogic Server 8.1 SP02, is a compatibility flag. It is used to specify whether a cmp-field of type byte[]
mapped to a OracleBlob should be serialized. By default, the value of the tag is false
, which means that the container will persist the byte[]
directly and not serialize it.
In versions prior to WebLogic Server 8.1 SP02, the default behavior was to serialize a cmp-field of type byte[] mapped to an OracleBlob. To revert to the old behavior, set the value of serialize-byte-array-to-oracle-blob
to true.
<compatibility>
<serialize-byte-array-to-oracle-blob>
true
</serialize-byte-array-to-oracle-blob>
</compatibility>
Note: This element is deprecated. To achieve the same functionality, use the SELECT DISTINCT
clause directly in finder queries
The sql-select-distinct
element controls whether the generated SQL SELECT statement will contain a a DISTINCT qualifier. Using the DISTINCT qualifier caused the database to return unique rows.
Oracle database does not allow use of a SELECT DISTINCT
with a FOR UPDATE
clause. Therefore, you cannot use the sql-select-distinct
element if any bean in the calling chain has a method with isolation-level
of TransactionReadCommittedForUpdate
. You specify the transaction-isolation
element in the weblogic-ejb-jar.xml
.
The XML
example contains the element shown here:
<sql-select-distinct>True</sql-select-dist
inct>
A CMP bean can be mapped to one or more DBMS tables. The table-map
element specifies a mapping between the cmp-fields of a bean and the columns of a table for all of the cmp-fields
mapped to that table. If you map a CMP bean to multiple DBMS tables, then you must specify a table-map
element for each the tables.
When you map a CMP bean to multiple tables, each table contains a row that maps to a particular bean instance. Consequently, all tables will contain the same number of rows at any point in time. In addition, each table contains the same set of homogeneous primary key values. Therefore, each table must have the same number of primary key columns and corresponding primary key columns in different tables must have the same type, although they may have different names.
Each table-map
element must specify a mapping from the primary key column(s) for a particular table to the primary key field(s) of the bean. You can only map non-primary key fields to a single table.
For information about using the verify-rows, verify-columns, and optimistic-column elements, see Check Data for Validity with Optimistic Concurrency
The XML
stanza can contain the elements shown here:
<table-map>
<table-nme>DeptTable</table-name>
<field-map>
<cmp-field>deptId1</cmp-field>
<dbms-column>t1_deptId1_column</dbms-column>
</field-map>
<field-map>
<cmp-field>deptId2</cmp-field>
<dbms-column>t1_deptId2_column</dbms-column>
</field-map>
<field-map>
<cmp-field>location</cmp-field>
<dbms-column>location_column</dbms-column>
</field-map>
<cmp-field>budget</cmp-field>
<dbms-column>budget</dbms-column>
</field-map>
<verify-rows>Read</verify-rows>
<verify-columns>Version</verify-columns>
<optimistic-column>ROW_VERSION
</optimistic-column>
</table-map>
The fully qualified SQL name of the table. The user defined for the data-source
for this bean must have read and write privileges for this table, but does not necessarily need schema modification privileges.
<weblogic-rdbms-jar>
<weblogic-rdbms-bean>
<ejb-name>containerManaged</ejb-name>
<data-source-name>examples-dataSource-demoPool</data-source-name>
<table-name>ejbAccounts</table-name>
</weblogic-rdbms-bean>
</weblogic-rdbms-jar>
Enforces pessimistic concurrency on a per-bean basis. Specifying True
causes SELECT ... FOR UPDATE
to be used whenever the bean is loaded from the database. This is different from the transaction isolation level of TransactionReadCommittedForUpdate
in that this is set at the bean level rather than the transaction level.
<weblogic-rdbms.jar>
<weblogic-rdbms-bean>
ejb-name>containerManaged</ejb-name>
<use-select-for-update>True</use-select-for-update>
</weblogic-rdbms-bean>
</weblogic-rdbms-jar>
The validate-db-schema-with
element specifies that container-managed persistence checks that beans have been mapped to a valid database schema during deployment.
If you specify MetaData
WebLogic Server uses the JDBC metadata to validate the schema.
If you specify TableQuery
, the default setting, WebLogic Server queries the tables directly to verify that they have the schema expected by CMP runtime.
The XML
stanza can contain the elements shown here:
<validate-db-schema-with>TableQuery</validate-db-schema-with>
The verify-columns
element specifies the columns in a table that you want WebLogic Server to check for validity when you use the optimistic
concurrency strategy. WebLogic Server checks columns at the end of a transaction, before committing it to the database, to make sure that no other transaction has modified the data.
See Choosing a Concurrency Strategy for more information.
<verify-columns>Modified</verify-columns>
The verify-rows
element specifies the rows in a table that the EJB container should check when optimistic concurrency is used.
Modified
— only rows that are updated or deleted by a transaction are checked. This value ensures that two transactions do not update the same row concurrently, resulting in a lost update, but allows reads and updates of different transactions to be interleaved. This results in a level of consistency that falls between the ANSI READ_COMMITTED
and REPEATABLE_READ
levels of consistency.Read
—specifies that any row that is read by the transaction should be checked. This includes both rows that are simply read and rows that are read and then updated or deleted by the transaction. Specifying a value of Read
results in additional overhead since it generally increases the amount of optimistic checking the EJB container must perform. With the Read
option, committed transactions read a set of rows that are guaranteed not to be modified by another transaction until after the transaction commits.This results in a high level of consistency which is very close to the ANSI definition of SERIALIZABLE
consistency.Note: If verify-rows
is set to Read
then the verify-columns
element may not have a value of Modified
, as this combination would result in the EJB container checking only the modified rows.
See Choosing a Concurrency Strategy for more information.
<verify-rows>Modified</verify-rows>
The weblogic-q
l element specifies a query that contains a WebLogic specific extension to the ejb-ql language. You should specify queries that only use standard EJB-QL language features in the ejb-jar.xml
deployment descriptor.
See weblogic-query.
The weblogic-query
element allows you to associate WebLogic specific attributes with a query, as necessary. For example, weblogic-query
can be used to specify a query that contains a WebLogic specific extension to EJB-QL. Queries that do not take advantage of WebLogic extensions to EJB-QL should be specified in the ejb-jar.xml
deployment descriptor.
Also, the weblogic-query
element is used to associate a field-group
with the query if the query retrieves an entity bean that should be pre-loaded into the cache by the query.
The XML
stanza can contain the elements shown here:
<weblogic-query>
<description>...</description>
<query-method>
<method-name>findBigAccounts</method-name>
<method-params>
<method-param>double</method-param>
</method-params>
<query-method>
<weblogic-ql>WHERE BALANCE>10000 ORDERBY NAME
</weblogic-ql>
<group-name>...</group-name>
<caching-name>...</caching-name>
<max-elements>...</max-elements>
<include-updates>...</include-updates>
<sql-select-distinct>...</sql-select-distinct>
</weblogic-query>
The weblogic-rdbms-bean
specifies an entity bean that is managed by the WebLogic RDBMS CMP persistence type.
weblogic-rdbms-bean
ejb-name
data-source-name
table-map
field-group
relationship-caching
weblogic-query
dalay-database-insert-until
automatic-key-generation
check-exists-on-method
The weblogic-rdbms-jar
element is the root level element of a WebLogic RDBMS CMP deployment descriptor. This element contains the deployment information for one or more entity beans and an optional set of relations.
The XML
structure of weblogic-rdbms-jar
is:
weblogic-rdbms-jar
weblogic-rdbms-bean
weblogic-rdbms-relation
create-default-dbms-tables
validate-db-schema-with
database-type
The weblogic-rdbms-relation
element represents a single relationship that is managed by the WebLogic CMP persistence type. deployment descriptor. WebLogic Server supports the following three relationship mappings:
For more information on container managed relationships, see Using Container-Managed Relationships (CMRs).
See the sections that following for examples of how one-to-one, one-to-many, and many-to-many relationships are configured.
Listing 8-3 shows the weblogic-rdbms-bean
stanza that defines a one-to-one relationship between the entities defined in Listing 8-1 and Listing 8-2. The weblogic-rdbms-relation
stanza is in the weblogic-cmp-jar.xml
file, after the weblogic-rdbms-bean
stanzas.
<weblogic-rdbms-bean>
<ejb-name>CountryEJB</ejb-name>
<data-source-name>wlsd21-datasource</data-source-name>
<table-map>
<table-name>EXAMPLE07_COUNTRY</table-name>
<field-map>
<cmp-field>name</cmp-field>
<dbms-column>NAME</dbms-column>
</field-map>
<field-map>
<cmp-field>continent</cmp-field>
<dbms-column>CONTINENT</dbms-column>
</field-map>
</table-map>
</weblogic-rdbms-bean>
<weblogic-rdbms-bean>
<ejb-name>CapitalEJB</ejb-name>
<data-source-name>wlsd21-datasource</data-source-name>
<table-map>
<table-name>EXAMPLE07_CAPITAL</table-name>
<field-map>
<cmp-field>CAPITAL_NAME</cmp-field>
<dbms-column>NAME</dbms-column>
</field-map>
<field-map>
<cmp-field>continent</cmp-field>
<dbms-column>CONTINENT</dbms-column>
</field-map>
</table-map>
</weblogic-rdbms-bean>
Listing 8-3 <weblogic-rdbms-relation> Stanza for a One-to-One Relationship
<weblogic-rdbms-relation>
<relation-name>CountryCapitalRel</relation-name>
<weblogic-relationship-role>
<relationship-role-name>CountryRole</relationship-role-name>
<relationship-role-map>
<column-map>
<foreign-key-column>CAPITAL_NAME</foreign-key-column>
<key-column>NAME</key-column>
</column-map>
</relationship-role-map>
</weblogic-relationship-role>
</weblogic-rdbms-relation>
Note: CAPITAL_NAME
is the column name for the foreign key in the Country table.
NAME
is the column name for the primary key located in the Capital table
<relationship-role-name> contains the relation field specified in <cmr-field
> in the <ejb-relationship-role
> stanza in ejb-jar.xml.
Listing 8-4 contains a sample <weblogic-rdbms-relation> stanza that defines a one-to-many relationship:
Listing 8-4 <weblogic-rdbms-relation> Stanza for a One-to-Many Relationship
<weblogic-rdbms-relation>
<relation-name>OwnerDogRel</relation-name>
<weblogic-relationship-role>
<relationship-role-name>DogRole</relationship-role-name>
<relationship-role-map>
<column-map>
<foreign-key-column>OWNER_NAME</foreign-<key-column>
<key-column>NAME</key-column>
</column-map>
<relationship-role-map>
</weblogic-relationship-role>
</weblogic-rdbms-relation>
Note: <relationship-role-name> contains the relation field specified in <cmr-field
> in the <ejb-relationship-role
> stanza in ejb-jar.xml.
<foreign-key-column> must specify the column in the table on the "many" side of the relationship.
A WebLogic Server many-to-many relationship involves the physical mapping of a join table. Each row in the join table contains two foreign keys that maps to the primary keys of the entities involved in the relationship.
The following example shows a many-to-many relationship between the FRIENDS
bean and the EMPLOYEES
bean.
Listing 8-5 <weblogic-rdbms-relation> Stanza for a Many-to-Many Relationship
<weblogic-rdbms-relation>
<relation-name>friends</relation-name>
<table-name>FRIENDS</table-name>
<weblogic-relationship-role>
<relationship-role-name>friend</relationship-role-name>
<relationship-role-map>
<column-map>
<foreign-key-column>first-friend-id</foreign-key-column>
<key-column>id</key-column>
</column-map
</relationship-role-map>
</weblogic-relationship-role>
<weblogic-relationship-role>
<relationship-role-name>second-friend</relationship-role-name>
<relationship-role-map>
<column-map>
<foreign-key-column>second-friend-id</foreign-key-column>
<key-column>id</key-column>
</column-map>
</relationship-role-map>
</weblogic-relationship-role>
</weblogic-rdbms-relation>
In Figure 8-4, the FRIENDS
join table has two columns, called first-friend-id
and second-friend-id.
Each column contains a foreign key that designates a particular employee who is a friend of another employee. The primary key column (key-column
) of the EMPLOYEES
table is id
. For this example, assume that the EMPLOYEES
bean is mapped to a single table. If the EMPLOYEES
bean is mapped to multiple tables, then the table containing the primary key column (key-column
) must be specified in the relationship-role-map
. For more information, see relationship-role-map.
The weblogic-relationship-role
element specifies the following DBMS schema information for an ejb-relationship-role
specified in ejb-jar.xml
:
relationship-role-map
sub-element specifies the mapping between a foreign key and a primary key, for one side of a relationship. For a 1-1 or 1-n relationship, only the role on the foreign-key side of the relationship specifies a mapping. Both roles specify a mapping for a m-m relationship. For details and examples, see relationship-role-map. group-name
can be used to indicate the field-group to be loaded when the bean corresponding to the role is loaded as a result of traversing the relationship, i.e. calling a cmr getXXX
method. db-cascade-delete
tag can to used to specify that cascade deletes use the built-in cascade delete facilities of the underlying DBMS. For more information, see db-cascade-delete.For more information about container-managed relationships, see Using Container-Managed Relationships (CMRs).
<weblogic-relationship-role>
<relationship-role-name>...</relationship-role-name>
<group-name> ....</group-name>
<relationship-role-map>...
....
</relationship-role-map>
<db-cascade-delete/>
</weblogic-relationship-role>