Sun GlassFish Enterprise Server 2.1 Developer's Guide

Chapter 7 Using the Java Persistence API

Sun GlassFish Enterprise Server support for the Java Persistence API includes all required features described in the Java Persistence Specification. Although officially part of the Enterprise JavaBeans Specification v3.0, also known as JSR 220, the Java Persistence API can also be used with non-EJB components outside the EJB container.

The Java Persistence API provides an object/relational mapping facility to Java developers for managing relational data in Java applications. For basic information about the Java Persistence API, see “Part Four: Persistence” in the Java EE 5 Tutorial.

This chapter contains Enterprise Server specific information on using the Java Persistence API in the following topics:


Note –

The default persistence provider in the Enterprise Server is based on Oracle's TopLink Essentials Java Persistence API implementation. All configuration options in TopLink Essentials are available to applications that use the Enterprise Server's default persistence provider.


Specifying the Database

The Enterprise Server uses the bundled Java DB (Derby) database by default. If the transaction-type element is omitted or specified as JTA and both the jta-data-source and non-jta-data-source elements are omitted in the persistence.xml file, Java DB is used as a JTA data source. If transaction-type is specified as RESOURCE_LOCAL and both jta-data-source and non-jta-data-source are omitted, Java DB is used as a non-JTA data source.

To use a non-default database, either specify a value for the jta-data-source element, or set the transaction-type element to RESOURCE_LOCAL and specify a value for the non-jta-data-source element.

If you are using the default persistence provider, the provider attempts to automatically detect the database based on the connection metadata. You can specify the optional toplink.platform.class.name property to guarantee that the database is correct. For example:

<?xml version="1.0" encoding="UTF-8"?>
    <persistence xmlns="http://java.sun.com/xml/ns/persistence">
        <persistence-unit name ="em1">
            <jta-data-source>jdbc/MyDB2DB</jta-data-source>
            <properties>
                <property name="toplink.platform.class.name" 
                    value="oracle.toplink.essentials.platform.database.DB2Platform"/>
            </properties>
        </persistence-unit>
    </persistence>

The following toplink.platform.class.name property values are allowed. Supported platforms have been tested with the Enterprise Server and are found to be Java EE compatible.

//Supported platforms
oracle.toplink.essentials.platform.database.DerbyPlatform
oracle.toplink.essentials.platform.database.oracle.OraclePlatform
oracle.toplink.essentials.platform.database.SQLServerPlatform
oracle.toplink.essentials.platform.database.DB2Platform
oracle.toplink.essentials.platform.database.SybasePlatform
oracle.toplink.essentials.platform.database.CloudscapePlatform
oracle.toplink.essentials.platform.database.MySQL4Platform
oracle.toplink.essentials.platform.database.PointBasePlatform
oracle.toplink.essentials.platform.database.PostgreSQLPlatform

//Others available
oracle.toplink.essentials.platform.database.InformixPlatform
oracle.toplink.essentials.platform.database.TimesTenPlatform
oracle.toplink.essentials.platform.database.AttunityPlatform
oracle.toplink.essentials.platform.database.HSQLPlatform
oracle.toplink.essentials.platform.database.SQLAnyWherePlatform
oracle.toplink.essentials.platform.database.DBasePlatform
oracle.toplink.essentials.platform.database.DB2MainframePlatform
oracle.toplink.essentials.platform.database.AccessPlatform

To use the Java Persistence API outside the EJB container (in Java SE mode), do not specify the jta-data-source or non-jta-data-source elements if the DataSource is not available. Instead, specify the provider element and any additional properties required by the JDBC driver or the database. For example:

<?xml version="1.0" encoding="UTF-8"?>
    <persistence xmlns="http://java.sun.com/xml/ns/persistence">
        <persistence-unit name ="em2">
            <provider>oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider</provider>
            <transaction-type>RESOURCE_LOCAL<transaction-type>
            <non-jta-data-source>jdbc/MyDB2DB</non-jta-data-source>
            <properties>
                <property name="toplink.platform.class.name" 
                    value="oracle.toplink.essentials.platform.database.DB2Platform"/>
                <!-- JDBC connection properties -->
                <property name="toplink.jdbc.driver" value="org.apache.derby.jdbc.ClientDriver"/>
                <property name="toplink.jdbc.url" 
value="jdbc:derby://localhost:1527/testdb;retrieveMessagesFromServerOnGetMessage=true;create=true;"/>
                <property name="toplink.jdbc.user" value="APP"/>
                <property name="toplink.jdbc.password" value="APP"/>
            </properties>
        </persistence-unit>
    </persistence>

For more information about toplink properties, see Additional Database Properties.

For a list of the JDBC drivers currently supported by the Enterprise Server, see the Sun GlassFish Enterprise Server 2.1 Release Notes. For configurations of supported and other drivers, see Configurations for Specific JDBC Drivers in Sun GlassFish Enterprise Server 2.1 Administration Guide.

To change the persistence provider, see Changing the Persistence Provider.

Additional Database Properties

If you are using the default persistence provider, you can specify in the persistence.xml file the database properties listed at Persistence Unit Extensions in TopLink JPA Extensions Reference.

For schema generation properties, see Generation Options. For query hints, see Query Hints.

Configuring the Cache

If you are using the default persistence provider, you can configure whether caching occurs, the type of caching, the size of the cache, and whether client sessions share the cache. Caching properties for the default persistence provider are described in detail at Extensions for Caching in TopLink JPA Extensions Reference.

Setting the Logging Level

One of the default persistence provider's database properties that you can set in the persistence.xml file is toplink.logging.level. For example, setting the logging level to FINE or higher logs all SQL statements. For details about this property, see Extensions for Logging inTopLink JPA Extensions Reference.

You can also set the TopLink Essentials logging level globally in the Application Server in any of the following ways:

Setting the logging level to OFF disables TopLink Essentials logging. A logging level set in the persistence.xml file takes precedence over the global logging level.

You can set the logging level for Java Persistence in general using the Admin Console. In the developer profile, select the Application Server component and the Logging tab. In the cluster profile, select the Logger Settings component under the relevant configuration. Select the Log Levels tab. Then set the logging level for Persistence. Setting the logging level to OFF disables Java Persistence logging.

Using Lazy Loading

The default persistence provider treats only OneToOne, ManyToOne, OneToMany, and ManyToMany mappings specially when they are annotated as LAZY. OneToMany and ManyToMany mappings are loaded lazily by default in compliance with the Java Persistence Specification. Other mappings are always loaded eagerly. For OneToOne and ManyToOne mappings, value holder indirection is used. For OneToMany and ManyToMany mappings, transparent indirection is used.

For basic information about lazy loading, see Lazy Loading in TopLink JPA Extensions Reference. For details about indirection, see Indirection in Mapping Concepts.

Primary Key Generation Defaults

In the descriptions of the @GeneratedValue, @SequenceGenerator, and @TableGenerator annotations in the Java Persistence Specification, certain defaults are noted as specific to the persistence provider. The default persistence provider's primary key generation defaults are listed here.

@GeneratedValue defaults are as follows:

The @SequenceGenerator annotation has one default specific to the default provider. The default sequenceName is the specified name.

@TableGenerator defaults are as follows:

Automatic Schema Generation

The automatic schema generation feature of the Enterprise Server defines database tables based on the fields or properties in entities and the relationships between the fields or properties. This insulates developers from many of the database related aspects of development, allowing them to focus on entity 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. This section covers the following topics:


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. Instead, an error is written to the server log. 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.


Annotations

The following annotations are used in automatic schema generation: @AssociationOverride, @AssociationOverrides, @AttributeOverride, @AttributeOverrides, @Column, @DiscriminatorColumn, @DiscriminatorValue, @Embedded, @EmbeddedId, @GeneratedValue, @Id, @IdClass, @JoinColumn, @JoinColumns, @JoinTable, @Lob, @ManyToMany, @ManyToOne, @OneToMany, @OneToOne, @PrimaryKeyJoinColumn, @PrimaryKeyJoinColumns, @SecondaryTable, @SecondaryTables, @SequenceGenerator, @Table, @TableGenerator, @UniqueConstraint, and @Version. For information about these annotations, see the Java Persistence Specification.

For @Column annotations, the insertable and updatable elements are not used in automatic schema generation.

For @OneToMany and @ManyToOne annotations, no ForeignKeyConstraint is created in the resulting DDL files.

Supported Data Types

The following table shows mappings of Java types to SQL types when the default persistence provider and automatic schema generation are used.

Table 7–1 Java Type to SQL Type Mappings

Java Type 

Java DB, Derby, CloudScape 

Oracle 

DB2 

Sybase 

MS-SQL Server 

MySQL Server 

boolean, java.lang.Boolean

SMALLINT

NUMBER(1)

SMALLINT

BIT

BIT

TINYINT(1)

int, java.lang.Integer

INTEGER

NUMBER(10)

INTEGER

INTEGER

INTEGER

INTEGER

long, java.lang.Long

BIGINT

NUMBER(19)

INTEGER

NUMERIC(19)

NUMERIC(19)

BIGINT

float, java.lang.Float

FLOAT

NUMBER(19,4)

FLOAT

FLOAT(16)

FLOAT(16)

FLOAT

double, java.lang.Double

FLOAT

NUMBER(19,4)

FLOAT

FLOAT(32)

FLOAT(32)

DOUBLE

short, java.lang.Short

SMALLINT

NUMBER(5)

SMALLINT

SMALLINT

SMALLINT

SMALLINT

byte, java.lang.Byte

SMALLINT

NUMBER(3)

SMALLINT

SMALLINT

SMALLINT

SMALLINT

java.lang.Number

DECIMAL

NUMBER(38)

DECIMAL(15)

NUMERIC(38)

NUMERIC(28)

DECIMAL(38)

java.math.BigInteger

BIGINT

NUMBER(38)

BIGINT

NUMERIC(38)

NUMERIC(28)

BIGINT

java.math.BigDecimal

DECIMAL

NUMBER(38)

DECIMAL(15)

NUMERIC(38)

NUMERIC(28)

DECIMAL(38)

java.lang.String

VARCHAR(255)

VARCHAR(255)

VARCHAR(255)

VARCHAR(255)

VARCHAR(255)

VARCHAR(255)

char, java.lang.Character

CHAR(1)

CHAR(1)

CHAR(1)

CHAR(1)

CHAR(1)

CHAR(1)

byte[], java.lang.Byte[], java.sql.Blob

BLOB(64000)

LONG RAW

BLOB(64000)

IMAGE

IMAGE

BLOB(64000)

char[], java.lang.Character[], java.sql.Clob

CLOB(64000)

LONG

CLOB(64000)

TEXT

TEXT

TEXT(64000)

java.sql.Date

DATE

DATE

DATE

DATETIME

DATETIME

DATE

java.sql.Time

TIME

DATE

TIME

DATETIME

DATETIME

TIME

java.sql.Timestamp

TIMESTAMP

DATE

TIMESTAMP

DATETIME

DATETIME

DATETIME

Generation Options

Schema generation properties or asadmin command line options can control automatic schema generation by the following:


Note –

Before using these options, make sure you have a properly configured database. See Specifying the Database.


The following optional schema generation properties control the automatic creation of database tables at deployment. You can specify them in the persistence.xml file.

Table 7–2 Schema Generation Properties

Property 

Default 

Description 

toplink.ddl-generation

none

Specifies whether tables and DDL files are created during deployment, and whether tables are dropped first if they already exist. Allowed values are create-tables, drop-and-create-tables, and none.

If create-tables is specified, database tables are created for entities that need them.

If drop-and-create-tables is specified, and if tables were automatically created when this application was last deployed, tables from the earlier deployment are dropped and fresh ones are created. If tables were not automatically created when this application was last deployed, no attempt is made to drop any tables. If tables with the same names as those that would have been automatically created are found, the deployment proceeds, but a warning is thrown to indicate that tables could not be created.

If none is specified, no tables are created or dropped.

The asadmin generation options listed in Table 7–3 and Table 7–4 override the value of this property.

If you are using persistence outside the EJB container and would like to create the DDL files without creating tables, additionally define a Java system property INTERACT_WITH_DB and set its value to false.

toplink.create-ddl-jdbc-file-name

createDDL.jdbc

Specifies the name of the JDBC file that contains the DDL statements required to create the required objects (tables, sequences, and constraints) in the database. 

toplink.drop-ddl-jdbc-file-name

dropDDL.jdbc

Specifies the name of the JDBC file that contains the DDL statements required to drop the required objects (tables, sequences, and constraints) from the database. 

toplink.application-location

. for the current working directory

Specifies the location where the DDL files are written. 

For persistence within the EJB container, if this property is not set, DDL files are written to one of the following locations, for applications and modules, respectively: 

domain-dir/generated/ejb/j2ee-apps/app-name

domain-dir/generated/ejb/j2ee-modules/mod-name

toplink.ddl-generation.output-mode

both

Specifies the DDL generation target if you are in Java SE mode, outside the EJB container. Values are as follows: 

  • both – Generates SQL files and executes them on the database. If toplink.ddl-generation is set to create-tables, then toplink.create-ddl-jdbc-file-name is written to toplink.application-location and executed on the database. If toplink.ddl-generation is set to drop-and-create-tables, then both toplink.create-ddl-jdbc-file-name and toplink.drop-ddl-jdbc-file-name are written to toplink.application-location and both SQL files are executed on the database.

  • database – Executes SQL on the database only (does not generate SQL files). If toplink.ddl-generation is set to create-tables, then toplink.create-ddl-jdbc-file-name is executed on the database. It is not written to toplink.application-location. If toplink.ddl-generation is set to drop-and-create-tables, then both toplink.create-ddl-jdbc-file-name and toplink.drop-ddl-jdbc-file-name are executed on the database. Neither is written to toplink.application-location.

  • sql-script – Generates SQL files only (does not execute them on the database). If toplink.ddl-generation is set to create-tables, then toplink.create-ddl-jdbc-file-name is written to toplink.application-location. It is not executed on the database. If toplink.ddl-generation is set to drop-and-create-tables, then both toplink.create-ddl-jdbc-file-name and toplink.drop-ddl-jdbc-file-name are written to toplink.application-location. Neither is executed on the database.

The following options of the asadmin deploy or asadmin deploydir command control the automatic creation of database tables at deployment.

Table 7–3 The asadmin deploy and asadmin deploydir Generation Options

Option 

Default 

Description 

--createtables

none 

If true, causes database tables to be created for entities that need them. If false, does not create tables. If not specified, the value of the toplink.ddl-generation property in persistence.xml is used.

--dropandcreatetables

none 

If true, and if tables were automatically created when this application was last deployed, tables from the earlier deployment are dropped and fresh ones are created.

If true, and if tables were not automatically created when this application was last deployed, no attempt is made to drop any tables. If tables with the same names as those that would have been automatically created are found, the deployment proceeds, but a warning is thrown to indicate that tables could not be created.

If false, the toplink.ddl-generation property setting in persistence.xml is overridden.

The following options of the asadmin undeploy command control the automatic removal of database tables at undeployment.

Table 7–4 The asadmin undeploy Generation Options

Option 

Default 

Description 

--droptables

none 

If true, causes database tables that were automatically created when the entities were last deployed to be dropped when the entities are undeployed. If false, does not drop tables.

If not specified, tables are dropped only if the toplink.ddl-generation property setting in persistence.xml is drop-and-create-tables.

For more information about the asadmin deploy, asadmin deploydir, and asadmin undeploy commands, see the Sun GlassFish Enterprise Server 2.1 Reference Manual.

When asadmin deployment options and persistence.xml options are both specified, the asadmin deployment options take precedence.

The asant tasks sun-appserv-deploy and sun-appserv-undeploy are equivalent to asadmin deploy and asadmin undeploy, respectively. These asant tasks also override the persistence.xml options. For details, see Chapter 3, The asant Utility.

Query Hints

Query hints are additional, implementation-specific configuration settings. You can use hints in your queries in the following format:

setHint("hint-name", hint-value)

For example:

Customer customer = (Customer)entityMgr.
     createNamedQuery("findCustomerBySSN").
     setParameter("SSN", "123-12-1234").
     setHint("toplink.refresh", true).
     getSingleResult();

For more information about the query hints available with the default provider, see Query Hints in TopLink JPA Extensions Reference.

Changing the Persistence Provider


Note –

The previous sections in this chapter apply only to the default persistence provider. If you change the provider for a module or application, the provider-specific database properties, query hints, and schema generation features described in this chapter do not apply.

The verifier utility always uses the default provider to verify persistence settings. For information about the verifier utility, see The verifier Utility in Sun GlassFish Enterprise Server 2.1 Application Deployment Guide.


You can change the persistence provider for an application in the manner described in the Java Persistence API Specification.

First, install the provider. Copy the provider JAR files to the domain-dir/lib directory, and restart the Enterprise Server. For more information about the domain-dir/lib directory, see Using the Common Class Loader. The new persistence provider is now available to all modules and applications deployed on servers that share the same configuration. However, the default provider remains the same.

In your persistence unit, specify the provider and any properties the provider requires in the persistence.xml file. For example:

<?xml version="1.0" encoding="UTF-8"?>
    <persistence xmlns="http://java.sun.com/xml/ns/persistence">
        <persistence-unit name ="em3">
            <provider>com.company22.persistence.PersistenceProviderImpl</provider>
            <properties>
                <property name="company22.database.name" value="MyDB"/>
            </properties>
        </persistence-unit>
    </persistence>

Restrictions and Optimizations

This section discusses restrictions and performance optimizations that affect using the Java Persistence API.

Extended Persistence Context Failover

A reference to an extended persistence context in a stateful session bean or an HttpSession may not fail over successfully.

The Java Persistence API specification is not clear how the container and persistence provider should work together to passivate a stateful session bean with an extended persistence context in a stand-alone server instance. This also prevents successful serialization and storage of a reference to an extended persistence context in an HttpSession.

Even in a single-instance environment, if a stateful session bean is passivated, its extended persistence context could be lost when the stateful session bean is activated. In this environment, it is safe to store an extended persistence context in a stateful session bean only if you can safely disable stateful session bean passivation altogether. This is possible, but trade-offs in memory utilization must be carefully examined before choosing this option.

In a single-instance environment, it is safe to store a reference to an extended persistence context in an HttpSession.

Using @OrderBy with a Shared Session Cache

Setting @OrderBy on a ManyToMany or OneToMany relationship field in which a List represents the Many side doesn't work if the session cache is shared. Use one of the following workarounds:

Using BLOB or CLOB Types with the Inet Oraxo JDBC Driver

To use BLOB or CLOB data types larger than 4 KB for persistence using the Inet Oraxo JDBC Driver for Oracle Databases, you must set the database's streamstolob property value to true.

Database Case Sensitivity

Mapping references to column or table names must be in accordance with the expected column or table name case, and ensuring this is the programmer's responsibility. If column or table names are not explicitly specified for a field or entity, the Enterprise Server uses upper case column names by default, so any mapping references to the column or table names must be in upper case. If column or table names are explicitly specified, the case of all mapping references to the column or table names must be in accordance with the case used in the specified names.

The following are examples of how case sensitivity affects mapping elements that refer to columns or tables. Programmers must keep case sensitivity in mind when writing these mappings.

Unique Constraints

If column names are not explicitly specified on a field, unique constraints and foreign key mappings must be specified using uppercase references. For example:

@Table(name="Department", uniqueConstraints={ @UniqueConstraint ( columnNames= { "DEPTNAME" } ) } )

The other way to handle this is by specifying explicit column names for each field with the required case. For example:

@Table(name="Department", uniqueConstraints={ @UniqueConstraint ( columnNames= { "deptName" } ) } )
public class Department{ @Column(name="deptName") private String deptName; }

Otherwise, the ALTER TABLE statement generated by the Enterprise Server uses the incorrect case, and the creation of the unique constraint fails.

Foreign Key Mapping

Use @OneToMany(mappedBy="COMPANY") or specify an explicit column name for the Company field on the Many side of the relationship.

SQL Result Set Mapping

Use the following elements:

<sql-result-set-mapping name="SRSMName" >
   <entity-result entity-class="entities.someEntity" />
   <column-result name="UPPERCASECOLUMNNAME" />
</sql-result-set-mapping>

Or specify an explicit column name for the upperCaseColumnName field.

Named Native Queries and JDBC Queries

Column or table names specified in SQL queries must be in accordance with the expected case. For example, MySQL requires column names in the SELECT clause of JDBC queries to be uppercase, while PostgreSQL and Sybase require table names to be uppercase in all JDBC queries.

PostgreSQL Case Sensitivity

PostgreSQL stores column and table names in lower case. JDBC queries on PostgreSQL retrieve column or table names in lowercase unless the names are quoted. For example:

use aliases Select m.ID AS \"ID\" from Department m

Use the backslash as an escape character in the class file, but not in the persistence.xml file.

Sybase Finder Limitation

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.

MySQL Database Restrictions

The following restrictions apply when you use a MySQL database with the Enterprise Server for persistence.