type=page status=published title=Using Container-Managed Persistence next=java-clients.html prev=ejb.html ~~
This chapter contains information on how EJB 2.1 container-managed persistence (CMP) works in {productName}.
The following topics are addressed here:
Note
|
The Web Profile of the {productName} supports the EJB 3.1 Lite
specification, which allows enterprise beans within web applications,
among other features. The full {productName} supports the entire EJB
3.1 specification. For details, see
JSR 318
( |
{productName} support for EJB 2.1 CMP beans includes:
-
Full support for the J2EE v1.4 specification’s CMP model. Extensive information on CMP is contained in chapters 10, 11, and 14 of the Enterprise JavaBeans Specification, v2.1. This includes the following:
-
Support for commit options B and C for transactions. See Commit Options.
-
The primary key class must be a subclass of
java.lang.Object
. This ensures portability, and is noted because some vendors allow primitive types (such asint
) to be used as the primary key class.
-
-
The {productName} CMP implementation, which provides the following:
-
An Object/Relational (O/R) mapping tool that creates XML deployment descriptors for EJB JAR files that contain beans that use CMP.
-
Support for compound (multi-column) primary keys.
-
Support for sophisticated custom finder methods.
-
Standards-based query language (EJB QL).
-
CMP runtime support. See Configuring the CMP Resource.
-
-
{productName} performance-related features, including the following:
-
Version column consistency checking
-
Relationship prefetching
-
Read-Only Beans
For details, see Performance-Related Features.
-
Implementation for entity beans that use CMP is mostly a matter of mapping CMP fields and CMR fields (relationships) to the database.
The following topics are addressed here:
Mapping refers to the ability to tie an object-based model to a relational model of data, usually the schema of a relational database. The CMP implementation provides the ability to tie a set of interrelated beans containing data and associated behaviors to the schema. This object representation of the database becomes part of the Java application. You can also customize this mapping to optimize these beans for the particular needs of an application. The result is a single data model through which both persistent database information and regular transient program data are accessed.
The mapping capabilities provided by the {productName} include:
-
Mapping a CMP bean to one or more tables
-
Mapping CMP fields to one or more columns
-
Mapping CMP fields to different column types
-
Mapping tables with compound primary keys
-
Mapping tables with unknown primary keys
-
Mapping CMP relationships to foreign keys
-
Mapping tables with overlapping primary and foreign keys
Each module with CMP beans must have the following files:
-
ejb-jar.xml
- The J2EE standard file for assembling enterprise beans. For a detailed description, see the Enterprise JavaBeans Specification, v2.1. -
glassfish-ejb-jar.xml
- The {productName} standard file for assembling enterprise beans. For a detailed description, see "The glassfish-ejb-jar.xml File" in {productName} Application Deployment Guide. -
sun-cmp-mappings.xml
- The mapping deployment descriptor file, which describes the mapping of CMP beans to tables in a database. For a detailed description, see "The sun-cmp-mappings.xml File" in {productName} Application Deployment Guide.
The sun-cmp-mappings.xml
file can be automatically generated and does
not have to exist prior to deployment. For details, see
Generation Options for CMP.
The sun-cmp-mappings.xml
file maps CMP fields and CMR fields
(relationships) to the database. A primary table must be selected for
each CMP bean, and optionally, multiple secondary tables. CMP fields are
mapped to columns in either the primary or secondary table(s). CMR
fields are mapped to pairs of column lists (normally, column lists are
the lists of columns associated with primary and foreign keys).
Note
|
Table names in databases can be case-sensitive. Make sure that the table
names in the Relationships should always be mapped to the primary key field(s) of the related table. |
The sun-cmp-mappings.xml
file conforms to the
sun-cmp-mapping_1_2.dtd
file and is packaged with the user-defined
bean classes in the EJB JAR file under the META-INF
directory.
The {productName} creates the mappings in the sun-cmp-mappings.xml
file automatically during deployment if the file is not present.
To map the fields and relationships of your entity beans manually, edit
the sun-cmp-mappings.xml
deployment descriptor. Only do this if you
are proficient in editing XML.
The mapping information is developed in conjunction with the database
schema (.dbschema
) file, which can be automatically captured when you
deploy the bean (see Automatic Database Schema Capture).
You can manually generate the schema using the capture-schema
utility
(Using the capture-schema
Utility).
The following topics are addressed here:
The data types used in automatic schema generation are also suggested for manual mapping. These data types are described in Supported Data Types for CMP.
Use of join tables in the database schema is supported for all types of relationships, not just many-to-many relationships. For general information about relationships, see section 10.3.7 of the Enterprise JavaBeans Specification, v2.1.
The {productName} supports automatic primary key generation for EJB
1.1, 2.0, and 2.1 CMP beans. To specify automatic primary key
generation, give the prim-key-class
element in the ejb-jar.xml
file
the value java.lang.Object
. CMP beans with automatically generated
primary keys can participate in relationships with other CMP beans. The
{productName} does not support database-generated primary key values.
If the database schema is created during deployment, the {productName} creates the schema with the primary key column, then generates unique values for the primary key column at runtime.
If the database schema is not created during deployment, the primary key
column in the mapped table must be of type NUMERIC
with a precision of
19 or more, and must not be mapped to any CMP field. The {productName} generates unique values for the primary key column at runtime.
If an existing database table has a primary key column in which the
values vary in length, but the type is CHAR
instead of VARCHAR
, the
{productName} automatically trims any extra spaces when retrieving
primary key values. It is not a good practice to use a fixed length
CHAR
column as a primary key. Use this feature with schemas that
cannot be changed, such as a schema inherited from a legacy application.
A managed field is a CMP or CMR field that is mapped to the same database column as another CMP or CMR field. CMP fields mapped to the same column and CMR fields mapped to exactly the same column lists always have the same value in memory. For CMR fields that share only a subset of their mapped columns, changes to the columns affect the relationship fields in memory differently. Basically, the {productName} always tries to keep the state of the objects in memory synchronized with the database.
A managed field can have any fetched-with
subelement. If the
fetched-with
subelement is <default/>
, the
-DAllowManagedFieldsInDefaultFetchGroup
flag must be set to true
.
See Default Fetch Group Flags and
"fetched-with" in {productName}
Application Deployment Guide.
Binary Large Object (BLOB) is a data type used to store values that do
not correspond to other types such as numbers, strings, or dates. Java
fields whose types implement java.io.Serializable or are represented as
byte[]
can be stored as BLOBs.
If a CMP field is defined as Serializable, it is serialized into a
byte[]
before being stored in the database. Similarly, the value
fetched from the database is deserialized. However, if a CMP field is
defined as byte[]
, it is stored directly instead of being serialized
and deserialized when stored and fetched, respectively.
To enable BLOB support in the {productName} environment, define a CMP
field of type byte[]
or a user-defined type that implements the
java.io.Serializable interface. If you map the CMP bean to an existing
database schema, map the field to a column of type BLOB.
To use BLOB or CLOB data types larger than 4 KB for CMP using the Inet
Oraxo JDBC Driver for Oracle Databases, you must set the streamstolob
property value to true
.
For a list of the JDBC drivers currently supported by the {productName}, see the {productName} Release Notes. For configurations of supported and other drivers, see "Configuration Specifics for JDBC Drivers" in {productName} Administration Guide.
For automatic mapping, you might need to change the default BLOB column
length for the generated schema using the schema-generator-properties
element in glassfish-ejb-jar.xml
. See your database vendor
documentation to determine whether you need to specify the length. For
example:
<schema-generator-properties>
<property>
<name>Employee.voiceGreeting.jdbc-type</name>
<value>BLOB</value>
</property>
<property>
<name>Employee.voiceGreeting.jdbc-maximum-length</name>
<value>10240</value>
</property>
...
</schema-generator-properties>
Character Large Object (CLOB) is a data type used to store and retrieve very long text fields. CLOBs translate into long strings.
To enable CLOB support in the {productName} environment, define a CMP
field of type java.lang.String
. If you map the CMP bean to an existing
database schema, map the field to a column of type CLOB.
To use BLOB or CLOB data types larger than 4 KB for CMP using the Inet
Oraxo JDBC Driver for Oracle Databases, you must set the streamstolob
property value to true
.
For a list of the JDBC drivers currently supported by the {productName}, see the {productName} Release Notes. For configurations of supported and other drivers, see "Configuration Specifics for JDBC Drivers" in {productName} Administration Guide.
For automatic mapping, you might need to change the default CLOB column
length for the generated schema using the schema-generator-properties
element in glassfish-ejb-jar.xml
. See your database vendor
documentation to determine whether you need to specify the length. For
example:
<schema-generator-properties>
<property>
<name>Employee.resume.jdbc-type</name>
<value>CLOB</value>
</property>
<property>
<name>Employee.resume.jdbc-maximum-length</name>
<value>10240</value>
</property>
...
</schema-generator-properties>
The automatic schema generation feature provided in the {productName} defines database tables based on the fields in entity beans and the relationships between the fields. This insulates developers from many of the database related aspects of development, allowing them to focus on entity bean development. The resulting schema is usable as-is or can be given to a database administrator for tuning with respect to performance, security, and so on.
The following topics are addressed here:
Note
|
Automatic schema generation is supported on an all-or-none basis: it expects that no tables exist in the database before it is executed. It is not intended to be used as a tool to generate extra tables or constraints. Deployment won’t fail if all tables are not created, and undeployment won’t fail if not all tables are dropped. This is done to allow you to investigate the problem and fix it manually. You should not rely on the partially created database schema to be correct for running the application. |
CMP supports a set of JDBC data types that are used in mapping Java data fields to SQL types. Supported JDBC data types are as follows: BIGINT, BIT, BLOB, CHAR, CLOB, DATE, DECIMAL, DOUBLE, FLOAT, INTEGER, NUMERIC, REAL, SMALLINT, TIME, TIMESTAMP, TINYINT, VARCHAR.
The following table contains the mappings of Java types to JDBC types when automatic mapping is used.
Table 9-1 Java Type to JDBC Type Mappings for CMP
Java Type | JDBC Type | Nullability |
---|---|---|
|
|
No |
|
|
Yes |
|
|
No |
|
|
Yes |
|
|
No |
|
|
Yes |
|
|
No |
|
|
Yes |
|
|
No |
|
|
Yes |
|
|
No |
|
|
Yes |
|
|
No |
|
|
Yes |
|
|
Yes |
|
|
Yes |
|
|
No |
|
|
Yes |
|
|
Yes |
Serializable |
|
Yes |
|
|
Yes |
|
|
Yes |
|
|
Yes |
|
|
Yes |
|
|
Yes |
Note
|
Java types assigned to CMP fields must be restricted to Java primitive
types, Java Serializable types, |
The following table contains the mappings of JDBC types to database vendor-specific types when automatic mapping is used. For a list of the JDBC drivers currently supported by the {productName}, see the {productName} Release Notes. For configurations of supported and other drivers, see "Configuration Specifics for JDBC Drivers" in {productName} Administration Guide.
Table 9-2 Mappings of JDBC Types to Database Vendor Specific Types for CMP
JDBC Type | Apache Derby, CloudScape | Oracle | DB2 | Sybase ASE 12.5 | MS-SQL Server |
---|---|---|---|---|---|
|
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Deployment descriptor elements or asadmin
command line options can
control automatic schema generation by the following:
-
Creating tables during deployment
-
Dropping tables during undeployment
-
Dropping and creating tables during redeployment
-
Specifying the database vendor
-
Specifying that table names are unique
-
Specifying type mappings for individual CMP fields
Note
|
Before using these options, make sure you have a properly configured CMP resource. See Configuring the CMP Resource. For a read-only bean, do not create the database schema during deployment. Instead, work with your database administrator to populate the data into the tables. See Using Read-Only Beans. Automatic schema generation is not supported for beans with version column consistency checking. Instead, work with your database administrator to create the schema and add the required triggers. See Version Column Consistency Checking. |
The following optional data subelements of the cmp-resource
element in
the glassfish-ejb-jar.xml
file control the automatic creation of
database tables at deployment. For more information about the
cmp-resource
element, see "cmp-resource" in
{productName} Application Deployment Guide and
Configuring the CMP Resource.
Table 9-3 The glassfish-ejb-jar.xml
Generation Elements
Element | Default | Description |
---|---|---|
|
If |
|
|
If |
|
none |
Specifies the name of the database vendor for which tables are created.
Allowed values are If no value is specified, a connection is made to the resource specified
by the |
|
none |
Specifies field-specific column attributes in bean-name`. For example:
Also allows you to set the For further information and an example, see "schema-generator-properties" in {productName} Application Deployment Guide. |
The following options of the asadmin deploy
or asadmin deploydir
command control the automatic creation of database tables at deployment.
Table 9-4 The asadmin deploy
and asadmin deploydir
Generation
Options for CMP
Option | Default | Description |
---|---|---|
|
none |
If |
|
none |
If If If |
|
none |
If |
|
none |
Specifies the name of the database vendor for which tables are created.
Allowed values are If not specified, the value of the If no value is specified, a connection is made to the resource specified
by the |
If one or more of the beans in the module are manually mapped and you
use any of the asadmin deploy
or asadmin deploydir
options, the
deployment is not harmed in any way, but the options have no effect, and
a warning is written to the server log.
The following options of the asadmin undeploy
command control the
automatic removal of database tables at undeployment.
Table 9-5 The asadmin undeploy
Generation Options for CMP
Option | Default | Description |
---|---|---|
|
none |
If If not specified, the value of the |
For more information about the asadmin deploy
, asadmin deploydir
,
and asadmin undeploy
commands, see the {productName} Reference Manual.
When command line and glassfish-ejb-jar.xml
options are both
specified, the asadmin
options take precedence.
The following topics are addressed here:
You can configure a CMP bean in {productName} to automatically
capture the database metadata and save it in a .dbschema
file during
deployment. If the sun-cmp-mappings.xml
file contains an empty
<schema/>
entry, the cmp-resource
entry in the
glassfish-ejb-jar.xml
file is used to get a connection to the
database, and automatic generation of the schema is performed.
Note
|
Before capturing the database schema automatically, make sure you have a properly configured CMP resource. See Configuring the CMP Resource. |
You can use the capture-schema
command to manually generate the
database metadata (.dbschema
) file. For details, see the
{productName} Reference Manual.
The capture-schema
utility does not modify the schema in any way. Its
only purpose is to provide the persistence engine with information about
the structure of the database (the schema).
Keep the following in mind when using the capture-schema
command:
-
The name of a
.dbschema
file must be unique across all deployed modules in a domain. -
If more than one schema is accessible for the schema user, more than one table with the same name might be captured if the
-schemaname
option ofcapture-schema
is not set. -
The schema name must be upper case.
-
Table names in databases are case-sensitive. Make sure that the table name matches the name in the database.
-
PostgreSQL databases internally convert all names to lower case. Before running the
capture-schema
command on a PostgreSQL database, make sure table and column names are lower case in thesun-cmp-mappings.xml
file. -
An Oracle database user running the
capture-schema
command needs ANALYZE ANY TABLE privileges if that user does not own the schema. These privileges are granted to the user by the database administrator.
An EJB module that contains CMP beans requires the JNDI name of a JDBC
resource in the jndi-name
subelement of the cmp-resource
element in
the glassfish-ejb-jar.xml
file. Set PersistenceManagerFactory
properties as properties of the cmp-resource
element in the
glassfish-ejb-jar.xml
file. See "cmp-resource" in
{productName} Application Deployment Guide.
In the Administration Console, open the Resources component, then select JDBC. Click the Help button in the Administration Console for information on creating a new JDBC resource.
For a list of the JDBC drivers currently supported by the {productName}, see the {productName} Release Notes. For configurations of supported and other drivers, see "Configuration Specifics for JDBC Drivers" in {productName} Administration Guide.
For example, if the JDBC resource has the JNDI name jdbc/MyDatabase
,
set the CMP resource in the glassfish-ejb-jar.xml
file as follows:
<cmp-resource>
<jndi-name>jdbc/MyDatabase</jndi-name>
</cmp-resource>
The {productName} provides the following features to enhance performance or allow more fine-grained data checking. These features are supported only for entity beans with container managed persistence.
The following topics are addressed here:
Note
|
Use of any of these features results in a non-portable application. |
The version consistency feature saves the bean state at first transactional access and caches it between transactions. The state is copied from the cache instead of being read from the database. The bean state is verified by primary key and version column values at flush for custom queries (for dirty instances only) and at commit (for clean and dirty instances).
-
Create the version column in the primary table.
-
Give the version column a numeric data type.
-
Provide appropriate update triggers on the version column.
These triggers must increment the version column on each update of the specified row. -
Specify the version column.
This is specified in thecheck-version-of-accessed-instances
subelement of theconsistency
element in thesun-cmp-mappings.xml
file. See "consistency" in {productName} Application Deployment Guide. -
Map the CMP bean to an existing schema.
Automatic schema generation is not supported for beans with version column consistency checking. Instead, work with your database administrator to create the schema and add the required triggers.
In many cases when an entity bean’s state is fetched from the database, its relationship fields are always accessed in the same transaction. Relationship prefetching saves database round trips by fetching data for an entity bean and those beans referenced by its CMR fields in a single database round trip.
To enable relationship prefetching for a CMR field, use the default
subelement of the fetched-with
element in the sun-cmp-mappings.xml
file. By default, these CMR fields are prefetched whenever
findByPrimaryKey
or a custom finder is executed for the entity, or
when the entity is navigated to from a relationship. (Recursive
prefetching is not supported, because it does not usually enhance
performance.) See "fetched-with" in {productName} Application Deployment Guide.
To disable prefetching for specific custom finders, use the
prefetch-disabled
element in the glassfish-ejb-jar.xml
file. See
"prefetch-disabled"
in {productName} Application Deployment Guide.
Multilevel relationship prefetching is supported for CMP 2.1 entity
beans. To enable multilevel relationship prefetching, set the following
property using the asadmin create-jvm-options
command:
asadmin create-jvm-options -Dcom.sun.jdo.spi.persistence.support.sqlstore.MULTILEVEL_PREFETCH=true
Another feature that the {productName} provides is the read-only bean, an entity bean that is never modified by an EJB client. Read-only beans avoid database updates completely.
Note
|
Read-only beans are specific to the {productName} and are not part of the Enterprise JavaBeans Specification, v2.1. Use of this feature for an EJB 2.1 bean results in a non-portable application. |
A read-only bean can be used to cache a database entry that is frequently accessed but rarely updated (externally by other beans). When the data that is cached by a read-only bean is updated by another bean, the read-only bean can be notified to refresh its cached data.
The {productName} provides a number of ways by which a read-only
bean’s state can be refreshed. By setting the
refresh-period-in-seconds
element in the glassfish-ejb-jar.xml
file
and the trans-attribute
element (or @TransactionAttribute
annotation) in the ejb-jar.xml
file, it is easy to configure a
read-only bean that is one of the following:
-
Always refreshed
-
Periodically refreshed
-
Never refreshed
-
Programmatically refreshed
Access to CMR fields of read-only beans is not supported. Deployment will succeed, but an exception will be thrown at runtime if a get or set method is invoked.
Read-only beans are best suited for situations where the underlying data never changes, or changes infrequently. For further information and usage guidelines, see Using Read-Only Beans.
Using the following flags can improve performance.
Setting -DAllowManagedFieldsInDefaultFetchGroup=true
allows CMP fields
that by default cannot be placed into the default fetch group to be
loaded along with all other fields that are fetched when the CMP state
is loaded into memory. These could be multiple fields mapped to the same
column in the database table, for example, an instance field and a CMR.
By default this flag is set to false
.
For additional information, see "level" in {productName} Application Deployment Guide.
Setting -DAllowMediatedWriteInDefaultFetchGroup
specifies how updated
CMP fields are written back to the database. If the flag is false
, all
fields in the CMP bean are written back to the database if at least one
field in the default fetch group has been changed in a transaction. If
the flag is true
, only fields modified by the bean are written back to
the database. Specifying true
can improve performance, particularly on
database tables with many columns that have not been updated. By default
this flag is set to false
.
To set one of these flags, use the asadmin create-jvm-options
command.
For example:
asadmin create-jvm-options -DAllowManagedFieldsInDefaultFetchGroup=true
The following topics are addressed here:
The Enterprise JavaBeans Specification, v1.1 does not specify the format of the finder method description. The {productName} uses an extension of Java Data Objects Query Language (JDOQL) queries to implement finder and selector methods. You can specify the following elements of the underlying JDOQL query:
-
Filter expression - A Java-like expression that specifies a condition that each object returned by the query must satisfy. Corresponds to the WHERE clause in EJB QL.
-
Query parameter declaration - Specifies the name and the type of one or more query input parameters. Follows the syntax for formal parameters in the Java language.
-
Query variable declaration - Specifies the name and type of one or more query variables. Follows the syntax for local variables in the Java language. A query filter might use query variables to implement joins.
-
Query ordering declaration - Specifies the ordering expression of the query. Corresponds to the ORDER BY clause of EJB QL.
The {productName} specific deployment descriptor
(glassfish-ejb-jar.xml
) provides the following elements to store the
EJB 1.1 finder method settings:
query-filter
query-params
query-variables
query-ordering
The bean developer uses these elements to construct a query. When the
finder method that uses these elements executes, the values of these
elements are used to execute a query in the database. The objects from
the JDOQL query result set are converted into primary key instances to
be returned by the EJB 1.1 ejbFind
method.
The JDO specification, JSR 12
(http://jcp.org/en/jsr/detail?id=12
), provides a comprehensive
description of JDOQL. The following information summarizes the elements
used to define EJB 1.1 finders.
The filter expression is a String containing a Boolean expression evaluated for each instance of the candidate class. If the filter is not specified, it defaults to true. Rules for constructing valid expressions follow the Java language, with the following differences:
-
Equality and ordering comparisons between primitives and instances of wrapper classes are valid.
-
Equality and ordering comparisons of Date fields and Date parameters are valid.
-
Equality and ordering comparisons of String fields and String parameters are valid.
-
White space (non-printing characters space, tab, carriage return, and line feed) is a separator and is otherwise ignored.
-
The following assignment operators are not supported.
-
Comparison operators such as =, +=, and so on
-
Pre- and post-increment
-
Pre- and post-decrement
-
-
Methods, including object construction, are not supported, except for these methods.
Collection.contains(Object o) Collection.isEmpty() String.startsWith(String s) String.endsWith(String e)
In addition, the {productName} supports the following nonstandard JDOQL methods.
String.like(String pattern) String.like(String pattern, char escape) String.substring(int start, int length) String.indexOf(String str) String.indexOf(String str, int start) String.length() Math.abs(numeric n) Math.sqrt(double d)
-
Navigation through a null-valued field, which throws a
NullPointerException
, is treated as if the sub-expression returnedfalse
.
Note
|
Comparisons between floating point values are by nature inexact.
Therefore, equality comparisons (== and !=) with floating point values
should be used with caution. Identifiers in the expression are
considered to be in the name space of the candidate class, with the
addition of declared parameters and variables. As in the Java language,
|
The following expressions are supported.
-
Relational operators (==, !=,>, <,>=, ⇐)
-
Boolean operators (&, &&, |, ||, ~, !)
-
Arithmetic operators (+, -, *, /)
-
String concatenation, only for String + String
-
Parentheses to explicitly mark operator precedence
-
Cast operator
-
Promotion of numeric operands for comparisons and arithmetic operations
The rules for promotion follow the Java rules extended by BigDecimal, BigInteger, and numeric wrapper classes. See the numeric promotions of the Java language specification.
The parameter declaration is a String containing one or more parameter type declarations separated by commas. This follows the Java syntax for method signatures.
This section provides a few query examples.
The following query returns all players called Michael. It defines a filter that compares the name field with a string literal:
name == "Michael"
The finder
element of the glassfish-ejb-jar.xml
file looks like
this:
<finder>
<method-name>findPlayerByName</method-name>
<query-filter>name == "Michael"</query-filter>
</finder>
This query returns all products in a specified price range. It defines two query parameters which are the lower and upper bound for the price: double low, double high. The filter compares the query parameters with the price field:
low < price && price < high
Query ordering is set to price ascending
.
The finder
element of the glassfish-ejb-jar.xml
file looks like
this:
<finder>
<method-name>findInRange</method-name>
<query-params>double low, double high</query-params>
<query-filter>low < price && price < high</query-filter>
<query-ordering>price ascending</query-ordering>
</finder>
This query returns all players having a higher salary than the player
with the specified name. It defines a query parameter for the name
java.lang.String name
. Furthermore, it defines a variable to which the
player’s salary is compared. It has the type of the persistence capable
class that corresponds to the bean:
mypackage.PlayerEJB_170160966_JDOState player
The filter compares the salary of the current player denoted by the
this
keyword with the salary of the player with the specified name:
(this.salary> player.salary) && (player.name == name)
The finder
element of the glassfish-ejb-jar.xml
file looks like
this:
<finder>
<method-name>findByHigherSalary</method-name>
<query-params>java.lang.String name</query-params>
<query-filter>
(this.salary > player.salary) && (player.name == name)
</query-filter>
<query-variables>
mypackage.PlayerEJB_170160966_JDOState player
</query-variables>
</finder>
This section discusses restrictions and performance optimizations that pertain to using CMP.
The following topics are addressed here:
EJB QL as defined in the EJB 2.1 Specification defines certain restrictions for the SELECT clause of an ORDER BY query (see section 11.2.8 ORDER BY Clause). This ensures that a query does not order by a field that is not returned by the query. By default, the EJB QL compiler checks the above restriction and throws an exception if the query does not conform.
However, some databases support SQL statements with an ORDER BY column
that is not included in the SELECT clause. To disable the validation of
the ORDER BY clause against the SELECT clause, set the
DISABLE_ORDERBY_VALIDATION
JVM option as follows:
asadmin create-jvm-options
-Dcom.sun.jdo.spi.persistence.support.ejb.ejbqlc.DISABLE_ORDERBY_VALIDATION=true
The DISABLE_ORDERBY_VALIDATION
option is set to false
by default.
Setting it to true
results in a non-portable module or application.
On DB2, the database configuration parameter APPLHEAPSZ
determines the
heap size. If you are using the Oracle or DataDirect database driver,
set this parameter to at least 2048
for CMP. For more information, see
http://publib.boulder.ibm.com/infocenter/db2luw/v8/index.jsp?topic=/com.ibm.db2.udb.doc/opt/tsbp2024.html
.
By default, the EJB container loads the state for all persistent fields
(excluding relationship, BLOB, and CLOB fields) before invoking the
ejbLoad
method of the abstract bean. This approach might not be
optimal for entity objects with large state if most business methods
require access to only parts of the state.
Use the fetched-with
element in sun-cmp-mappings.xml
for fields that
are used infrequently. See "fetched-with" in {productName} Application Deployment Guide.
The following restrictions apply to the remote interface of an EJB 2.1 bean that uses CMP:
-
Do not expose the
get
andset
methods for CMR fields or the persistence collection classes that are used in container-managed relationships through the remote interface of the bean.However, you are free to expose the
get
andset
methods that correspond to the CMP fields of the entity bean through the bean’s remote interface. -
Do not expose the container-managed collection classes that are used for relationships through the remote interface of the bean.
-
Do not expose local interface types or local home interface types through the remote interface or remote home interface of the bean.
Dependent value classes can be exposed in the remote interface or remote home interface, and can be included in the client EJB JAR file.
Case-sensitive behavior cannot be achieved for PostgreSQL databases. PostgreSQL databases internally convert all names to lower case, which makes the following workarounds necessary:
-
In the CMP 2.1 runtime, PostgreSQL table and column names are not quoted, which makes these names case insensitive.
-
Before running the
capture-schema
command on a PostgreSQL database, make sure table and column names are lower case in thesun-cmp-mappings.xml
file.
For EJB 2.1 beans, the lock-when-loaded
consistency level is
implemented by placing update locks on the data corresponding to a bean
when the data is loaded from the database. There is no suitable
mechanism available on Sybase databases to implement this feature.
Therefore, the lock-when-loaded
consistency level is not supported on
Sybase databases. See "consistency" in {productName} Application Deployment Guide.
If a finder method with an input greater than 255 characters is executed and the primary key column is mapped to a VARCHAR column, Sybase attempts to convert type VARCHAR to type TEXT and generates the following error:
com.sybase.jdbc2.jdbc.SybSQLException: Implicit conversion from datatype
'TEXT' to 'VARCHAR' is not allowed. Use the CONVERT function to run this query.
To avoid this error, make sure the finder method input is less than 255 characters.
If a field type is a Java date or time type (java.util.Date
,
java.sql.Date
, java.sql.Time
, java.sql.Timestamp
), make sure that
the field value exactly matches the value in the database.
For example, the following code uses a java.sql.Date
type as a primary
key field:
java.sql.Date myDate = new java.sql.Date(System.currentTimeMillis())
BeanA.create(myDate, ...);
For some databases, this code results in only the year, month, and date portion of the field value being stored in the database. Later if the client tries to find this bean by primary key as follows, the bean is not found in the database because the value does not match the one that is stored in the database.
myBean = BeanA.findByPrimaryKey(myDate);
Similar problems can happen if the database truncates the timestamp value while storing it, or if a custom query has a date or time value comparison in its WHERE clause.
For automatic mapping to an Oracle database, fields of type
java.util.Date
, java.sql.Date
, and java.sql.Time
are mapped to
Oracle’s DATE data type. Fields of type java.sql.Timestamp
are mapped
to Oracle’s TIMESTAMP(9)
data type.
For version consistency triggers on MSSQL, the property
RECURSIVE_TRIGGERS
must be set to false
, which is the default. If
set to true
, triggers throw a java.sql.SQLException
.
Set this property as follows:
EXEC sp_dboption 'database-name', 'recursive triggers', 'FALSE'
go
You can test this property as follows:
SELECT DATABASEPROPERTYEX('database-name', 'IsRecursiveTriggersEnabled')
go
The following restrictions apply when you use a MySQL database with the {productName} for persistence.
-
MySQL treats
int1
andint2
as reserved words. If you want to defineint1
andint2
as fields in your table, use\`int1`
and\`int2\`
field names in your SQL file. -
When
VARCHAR
fields get truncated, a warning is displayed instead of an error. To get an error message, start the MySQL database in strict SQL mode. -
The order of fields in a foreign key index must match the order in the explicitly created index on the primary table.
-
The
CREATE TABLE
syntax in the SQL file must end with the following line.) Engine=InnoDB;
InnoDB
provides MySQL with a transaction-safe (ACID compliant) storage engine having commit, rollback, and crash recovery capabilities. -
For a
FLOAT
type field, the correct precision must be defined. By default, MySQL uses four bytes to store aFLOAT
type that does not have an explicit precision definition. For example, this causes a number such as 12345.67890123 to be rounded off to 12345.7 during anINSERT
. To prevent this, specifyFLOAT(10,2)
in the DDL file, which forces the database to use an eight-byte double-precision column. For more information, seehttp://dev.mysql.com/doc/mysql/en/numeric-types.html
. -
To use
||
as the string concatenation symbol, start the MySQL server with the--sql-mode="PIPES_AS_CONCAT"
option. For more information, seehttp://dev.mysql.com/doc/refman/5.0/en/server-sql-mode.html
andhttp://dev.mysql.com/doc/mysql/en/ansi-mode.html
. -
MySQL always starts a new connection when
autoCommit==true
is set. This ensures that each SQL statement forms a single transaction on its own. If you try to rollback or commit an SQL statement, you get an error message.javax.transaction.SystemException: java.sql.SQLException: Can't call rollback when autocommit=true javax.transaction.SystemException: java.sql.SQLException: Error open transaction is not closed
To resolve this issue, add
relaxAutoCommit=true
to the JDBC URL. For more information, seehttp://forums.mysql.com/read.php?39,31326,31404
. -
Change the trigger create format from the following:
CREATE TRIGGER T_UNKNOWNPKVC1 BEFORE UPDATE ON UNKNOWNPKVC1 FOR EACH ROW WHEN (NEW.VERSION = OLD.VERSION) BEGIN :NEW.VERSION := :OLD.VERSION + 1; END; /
To the following:
DELIMITER | CREATE TRIGGER T_UNKNOWNPKVC1 BEFORE UPDATE ON UNKNOWNPKVC1 FOR EACH ROW WHEN (NEW.VERSION = OLD.VERSION) BEGIN :NEW.VERSION := :OLD.VERSION + 1; END | DELIMITER ;
For more information, see
http://dev.mysql.com/doc/mysql/en/create-trigger.html
. -
MySQL does not allow a
DELETE
on a row that contains a reference to itself. Here is an example that illustrates the issue.create table EMPLOYEE ( empId int NOT NULL, salary float(25,2) NULL, mgrId int NULL, PRIMARY KEY (empId), FOREIGN KEY (mgrId) REFERENCES EMPLOYEE (empId) ) ENGINE=InnoDB; insert into Employee values (1, 1234.34, 1); delete from Employee where empId = 1;
This example fails with the following error message.
ERROR 1217 (23000): Cannot delete or update a parent row: a foreign key constraint fails
To resolve this issue, change the table creation script to the following:
create table EMPLOYEE ( empId int NOT NULL, salary float(25,2) NULL, mgrId int NULL, PRIMARY KEY (empId), FOREIGN KEY (mgrId) REFERENCES EMPLOYEE (empId) ON DELETE SET NULL ) ENGINE=InnoDB; insert into Employee values (1, 1234.34, 1); delete from Employee where empId = 1;
This can be done only if the foreign key field is allowed to be null. For more information, see
http://dev.mysql.com/doc/mysql/en/innodb-foreign-key-constraints.html
. -
When an SQL script has foreign key constraints defined,
capture-schema
fails to capture the table information correctly. To work around the problem, remove the constraints and then runcapture-schema
. Here is an example that illustrates the issue.CREATE TABLE ADDRESSBOOKBEANTABLE (ADDRESSBOOKNAME VARCHAR(255) NOT NULL PRIMARY KEY, CONNECTEDUSERS BLOB NULL, OWNER VARCHAR(256), FK_FOR_ACCESSPRIVILEGES VARCHAR(256), CONSTRAINT FK_ACCESSPRIVILEGE FOREIGN KEY (FK_FOR_ACCESSPRIVILEGES) REFERENCES ACCESSPRIVILEGESBEANTABLE (ROOT) ) ENGINE=InnoDB;
To resolve this issue, change the table creation script to the following:
CREATE TABLE ADDRESSBOOKBEANTABLE (ADDRESSBOOKNAME VARCHAR(255) NOT NULL PRIMARY KEY, CONNECTEDUSERS BLOB NULL, OWNER VARCHAR(256), FK_FOR_ACCESSPRIVILEGES VARCHAR(256) ) ENGINE=InnoDB;