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# 9 Using Container-Managed Persistence

This chapter contains information on how EJB 2.1 container-managed persistence (CMP) works in Oracle GlassFish Server.

The following topics are addressed here:

- GlassFish Server Support for CMP

- CMP Mapping

- Automatic Schema Generation for CMP

- Schema Capture

- Configuring the CMP Resource

- Performance-Related Features

- Configuring Queries for 1.1 Finders

- CMP Restrictions and Optimizations

Note:

The Web Profile of the GlassFish Server supports the EJB 3.1 Lite specification, which allows enterprise beans within web applications, among other features. The full GlassFish Server supports the entire EJB 3.1 specification. For details, see JSR 318.

## GlassFish Server Support for CMP

GlassFish Server 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 as `int`) to be used as the primary key class.

- The GlassFish Server 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.

- GlassFish Server performance-related features, including the following:

  - Version column consistency checking

  - Relationship prefetching

  - Read-Only Beans

  For details, see Performance-Related Features.

## CMP Mapping

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 Capabilities

- The Mapping Deployment Descriptor File

- Mapping Considerations

### Mapping Capabilities

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 GlassFish Server 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

### The Mapping Deployment Descriptor File

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 GlassFish Server standard file for assembling enterprise beans. For a detailed description, see "The glassfish-ejb-jar.xml File" in Oracle GlassFish Server 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 Oracle GlassFish Server 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 `sun-cmp-mappings.xml` file match the names in the database.

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 GlassFish Server 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).

### Mapping Considerations

The following topics are addressed here:

- Join Tables and Relationships

- Automatic Primary Key Generation

- Fixed Length CHAR Primary Keys

- Managed Fields

- BLOB Support

- CLOB Support

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.

#### Join Tables and Relationships

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.

#### Automatic Primary Key Generation

The GlassFish Server 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 GlassFish Server does not support database-generated primary key values.

If the database schema is created during deployment, the GlassFish Server 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 GlassFish Server generates unique values for the primary key column at runtime.

#### Fixed Length CHAR Primary Keys

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 GlassFish Server 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.

#### Managed Fields

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 GlassFish Server 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 Oracle GlassFish Server Application Deployment Guide.

#### BLOB Support

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 GlassFish Server 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 GlassFish Server, see the Oracle GlassFish Server Release Notes. For configurations of supported and other drivers, see "Configuration Specifics for JDBC Drivers" in Oracle GlassFish Server 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>

#### CLOB Support

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 GlassFish Server 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 GlassFish Server, see the Oracle GlassFish Server Release Notes. For configurations of supported and other drivers, see "Configuration Specifics for JDBC Drivers" in Oracle GlassFish Server 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>

## Automatic Schema Generation for CMP

The automatic schema generation feature provided in the GlassFish Server 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:

- Supported Data Types for CMP

- Generation Options for CMP

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.

### Supported Data Types for CMP

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
--- | --- | ---
`boolean` | `BIT` | No
`java.lang.Boolean` | `BIT` | Yes
`byte` | `TINYINT` | No
`java.lang.Byte` | `TINYINT` | Yes
`double` | `DOUBLE` | No
`java.lang.Double` | `DOUBLE` | Yes
`float` | `REAL` | No
`java.lang.Float` | `REAL` | Yes
`int` | `INTEGER` | No
`java.lang.Integer` | `INTEGER` | Yes
`long` | `BIGINT` | No
`java.lang.Long` | `BIGINT` | Yes
`short` | `SMALLINT` | No
`java.lang.Short` | `SMALLINT` | Yes
`java.math.BigDecimal` | `DECIMAL` | Yes
`java.math.BigInteger` | `DECIMAL` | Yes
`char` | `CHAR` | No
`java.lang.Character` | `CHAR` | Yes
`java.lang.String` | `VARCHAR` or `CLOB` | Yes
Serializable | `BLOB` | Yes
`byte[]` | `BLOB` | Yes
`java.util.Date` | `DATE` (Oracle only) `TIMESTAMP` (all other databases) | Yes
`java.sql.Date` | `DATE` | Yes
`java.sql.Time` | `TIME` | Yes
`java.sql.Timestamp` | `TIMESTAMP` | Yes

Note:

Java types assigned to CMP fields must be restricted to Java primitive types, Java Serializable types, `java.util.Date`, `java.sql.Date`, `java.sql.Time`, or `java.sql.Timestamp`. An entity bean local interface type (or a collection of such) can be the type of a CMR field.

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 GlassFish Server, see the Oracle GlassFish Server Release Notes. For configurations of supported and other drivers, see "Configuration Specifics for JDBC Drivers" in Oracle GlassFish Server Administration Guide.

Table 9-2 Mappings of JDBC Types to Database Vendor Specific Types for CMP

JDBC Type | Java DB, Derby, CloudScape | Oracle | DB2 | Sybase ASE 12.5 | MS-SQL Server
--- | --- | --- | --- | --- | ---
`BIT` | `SMALLINT` | `SMALLINT` | `SMALLINT` | `TINYINT` | `BIT`
`TINYINT` | `SMALLINT` | `SMALLINT` | `SMALLINT` | `TINYINT` | `TINYINT`
`SMALLINT` | `SMALLINT` | `SMALLINT` | `SMALLINT` | `SMALLINT` | `SMALLINT`
`INTEGER` | `INTEGER` | `INTEGER` | `INTEGER` | `INTEGER` | `INTEGER`
`BIGINT` | `BIGINT` | `NUMBER` | `BIGINT` | `NUMERIC` | `NUMERIC`
`REAL` | `REAL` | `REAL` | `FLOAT` | `FLOAT` | `REAL`
`DOUBLE` | `DOUBLE PRECISION` | `DOUBLE PRECISION` | `DOUBLE` | `DOUBLE PRECISION` | `FLOAT`
`DECIMAL(p,s)` | `DECIMAL(p,s)` | `NUMBER(p,s)` | `DECIMAL(p,s)` | `DECIMAL(p,s)` | `DECIMAL(p,s)`
`VARCHAR` | `VARCHAR` | `VARCHAR2` | `VARCHAR` | `VARCHAR` | `VARCHAR`
`DATE` | `DATE` | `DATE` | `DATE` | `DATETIME` | `DATETIME`
`TIME` | `TIME` | `DATE` | `TIME` | `DATETIME` | `DATETIME`
`TIMESTAMP` | `TIMESTAMP` | `TIMESTAMP(9)` | `TIMESTAMP` | `DATETIME` | `DATETIME`
`BLOB` | `BLOB` | `BLOB` | `BLOB` | `IMAGE` | `IMAGE`
`CLOB` | `CLOB` | `CLOB` | `CLOB` | `TEXT` | `NTEXT`

### Generation Options for CMP

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 Oracle GlassFish Server Application Deployment Guide and Configuring the CMP Resource.

Table 9-3 The `glassfish-ejb-jar.xml` Generation Elements

Element | Default | Description
--- | --- | ---
`create-tables-at-deploy` | `false` | If `true`, causes database tables to be created for beans that are automatically mapped by the EJB container. No unique constraints are created. If `false`, does not create tables.
`drop-tables-at-undeploy` | `false` | If `true`, causes database tables that were automatically created when the bean(s) were last deployed to be dropped when the bean(s) are undeployed. If `false`, does not drop tables.
`database-vendor-name` | none | Specifies the name of the database vendor for which tables are created. Allowed values are `javadb`, `db2`, `mssql`, `mysql`, `oracle`, `postgresql`, `pointbase`, `derby` (also for CloudScape), and `sybase`, case-insensitive. If no value is specified, a connection is made to the resource specified by the `jndi-name` subelement of the `cmp-resource` element in the `glassfish-ejb-jar.xml` file, and the database vendor name is read. If the connection cannot be established, or if the value is not recognized, SQL-92 compliance is presumed.
`schema-generator-properties` | none | Specifies field-specific column attributes in `property` subelements. Each property name is of the following format: bean-name`.`field-name`.`attribute For example: `Employee.firstName.jdbc-type` Also allows you to set the `use-unique-table-names` property. If `true`, this property specifies that generated table names are unique within each GlassFish Server domain. The default is `false`. For further information and an example, see "schema-generator-properties" in Oracle GlassFish Server 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
--- | --- | ---
`--createtables` | none | If `true`, causes database tables to be created for beans that need them. No unique constraints are created. If `false`, does not create tables. If not specified, the value of the `create-tables-at-deploy` attribute in `glassfish-ejb-jar.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 indicates that tables could not be created. If `false`, settings of `create-tables-at-deploy` or `drop-tables-at-undeploy` in the `glassfish-ejb-jar.xml` file are overridden.
`--uniquetablenames` | none | If `true`, specifies that table names are unique within each GlassFish Server domain. If not specified, the value of the `use-unique-table-names` property in `glassfish-ejb-jar.xml` is used.
`--dbvendorname` | none | Specifies the name of the database vendor for which tables are created. Allowed values are `javadb`, `db2`, `mssql`, `oracle`, `postgresql`, `pointbase`, `derby` (also for CloudScape), and `sybase`, case-insensitive. If not specified, the value of the `database-vendor-name` attribute in `glassfish-ejb-jar.xml` is used. If no value is specified, a connection is made to the resource specified by the `jndi-name` subelement of the `cmp-resource` element in the `glassfish-ejb-jar.xml` file, and the database vendor name is read. If the connection cannot be established, or if the value is not recognized, SQL-92 compliance is presumed.

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
--- | --- | ---
`--droptables` | none | If `true`, causes database tables that were automatically created when the bean(s) were last deployed to be dropped when the bean(s) are undeployed. If `false`, does not drop tables. If not specified, the value of the `drop-tables-at-undeploy` attribute in `glassfish-ejb-jar.xml` is used.

For more information about the `asadmin deploy`, `asadmin deploydir`, and `asadmin undeploy` commands, see the Oracle GlassFish Server Reference Manual.

When command line and `glassfish-ejb-jar.xml` options are both specified, the `asadmin` options take precedence.

## Schema Capture

The following topics are addressed here:

- Automatic Database Schema Capture

- Using the `capture-schema` Utility

### Automatic Database Schema Capture

You can configure a CMP bean in GlassFish Server 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.

### Using the `capture-schema` Utility

You can use the `capture-schema` command to manually generate the database metadata (`.dbschema`) file. For details, see the Oracle GlassFish Server 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 of `capture-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 the `sun-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.

## Configuring the CMP Resource

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 Oracle GlassFish Server 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 GlassFish Server, see the Oracle GlassFish Server Release Notes. For configurations of supported and other drivers, see "Configuration Specifics for JDBC Drivers" in Oracle GlassFish Server 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>

## Performance-Related Features

The GlassFish Server 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:

- Version Column Consistency Checking

- Relationship Prefetching

- Read-Only Beans

- Default Fetch Group Flags

Note:

Use of any of these features results in a non-portable application.

### Version Column Consistency Checking

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).

#### To Use Version Consistency

1. Create the version column in the primary table.

2. Give the version column a numeric data type.

3. Provide appropriate update triggers on the version column.

   These triggers must increment the version column on each update of the specified row.

4. Specify the version column.

   This is specified in the `check-version-of-accessed-instances` subelement of the `consistency` element in the `sun-cmp-mappings.xml` file. See "consistency" in Oracle GlassFish Server Application Deployment Guide.

5. 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.

### Relationship Prefetching

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 Oracle GlassFish Server 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 Oracle GlassFish Server 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

### Read-Only Beans

Another feature that the GlassFish Server 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 GlassFish Server 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 GlassFish Server 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.

## Default Fetch Group Flags

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 Oracle GlassFish Server 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

## Configuring Queries for 1.1 Finders

The following topics are addressed here:

- About JDOQL Queries

- Query Filter Expression

- Query Parameters

- Query Variables

- JDOQL Examples

### About JDOQL Queries

The Enterprise JavaBeans Specification, v1.1 does not specify the format of the finder method description. The GlassFish Server 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 GlassFish Server 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, provides a comprehensive description of JDOQL. The following information summarizes the elements used to define EJB 1.1 finders.

### Query Filter Expression

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 GlassFish Server 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 returned `false`.

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, `this` is a reserved word, and refers to the current instance being evaluated.

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.

### Query Parameters

The parameter declaration is a String containing one or more parameter type declarations separated by commas. This follows the Java syntax for method signatures.

### Query Variables

The type declarations follow the Java syntax for local variable declarations.

### JDOQL Examples

This section provides a few query examples.

#### Example 1

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>

#### Example 2

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 &lt; price &amp;&amp; price &lt high</query-filter>
       <query-ordering>price ascending</query-ordering>
    </finder>

#### Example 3

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 &gt; player.salary) &amp;&amp; (player.name == name)
       </query-filter>
       <query-variables>
          mypackage.PlayerEJB_170160966_JDOState player
       </query-variables>
    </finder>

## CMP Restrictions and Optimizations

This section discusses restrictions and performance optimizations that pertain to using CMP.

The following topics are addressed here:

- Disabling ORDER BY Validation

- Setting the Heap Size on DB2

- Eager Loading of Field State

- Restrictions on Remote Interfaces

- PostgreSQL Case Insensitivity

- No Support for `lock-when-loaded` on Sybase

- Sybase Finder Limitation

- Date and Time Fields

- Set `RECURSIVE_TRIGGERS` to `false` on MSSQL

- MySQL Database Restrictions

### Disabling ORDER BY Validation

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.

### Setting the Heap Size on DB2

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.htm`.

### Eager Loading of Field State

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 Oracle GlassFish Server Application Deployment Guide.

### Restrictions on Remote Interfaces

The following restrictions apply to the remote interface of an EJB 2.1 bean that uses CMP:

- Do not expose the `get` and `set` 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` and `set` 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.

### PostgreSQL Case Insensitivity

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 the `sun-cmp-mappings.xml` file.

### No Support for `lock-when-loaded` on Sybase

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 Oracle GlassFish Server Application Deployment Guide.

### 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.

### Date and Time Fields

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.

### Set `RECURSIVE_TRIGGERS` to `false` on MSSQL

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

### MySQL Database Restrictions

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

- MySQL treats `int1` and `int2` as reserved words. If you want to define `int1` and `int2` 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 a `FLOAT` 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 an `INSERT`. To prevent this, specify `FLOAT(10,2)` in the DDL file, which forces the database to use an eight-byte double-precision column. For more information, see `http://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, see `http://dev.mysql.com/doc/refman/5.0/en/server-sql-mode.html` and `http://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, see `http://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 run `capture-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;