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<div style="float:right;border:1px solid #000000;padding:5px">__TOC__
[[Special:Whatlinkshere/Developing Applications Using EclipseLink JPA (ELUG)|Related Topics]]</div>


==Using Application Components==
When developing an application with EclipseLink JPA, you need to know how to use the following application components:
* [[#How to Obtain an Entity Manager Factory|Entity manager factory]]
* [[#How to Obtain an Entity Manager|Entity manager ]]
* [[#How to Use a Persistence Context|Persistence context ]]


===How to Obtain an Entity Manager Factory===
How you obtain the entity manager factory depends on the Java environment in which you are developing your application:
* [[#Obtaining an Entity Manager Factory in Java EE Application Server Environment|Obtaining an Entity Manager Factory in Java EE Application Server Environment]]
* [[#Obtaining an Entity Manager Factory in Java SE Environment|Obtaining an Entity Manager Factory in Java SE Environment]]


====Obtaining an Entity Manager Factory in Java EE Application Server Environment====
You can inject an entity manager factory using the <tt>@PersistenceUnit</tt> annotation, as the following example shows, or you can obtain it through JNDI lookup. You may choose to specify the <tt>unitName</tt> element to designate the persistence unit whose factory you are using.
 @PersistenceUnit
 EntityManagerFactory emf;

For more information, see the following:
* Section 8.4.2 "PersistenceUnit Annotation" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* Section 5.3.1 "Obtaining an Entity Manager Factory in a Java EE Container" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* [[Introduction%20to%20Java%20Persistence%20API%20(ELUG)#Container-Managed Entity Manager|Container-Managed Entity Manager]]


====Obtaining an Entity Manager Factory in Java SE Environment====
In Java SE environment, use the <tt>javax.persistence.Persistence</tt> bootstrap class to get access to an entity manager factory. In your application, create an entity manager factory by calling the <tt>javax.persistence.Persistence</tt> class' <tt>createEntityManagerFactory</tt> method (see Section 7.2.1 "javax.persistence.Persistence Class" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]), as the following example shows:
<source lang="java">
 EntityManagerFactory emf = javax.persistence.Persistence.createEntityManagerFactory("Order");
 EntityManager em = emf.createEntityManager();
</source>

For more information, see the following:
* Section 7.2.1 "javax.persistence.Persistence Class" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* Section 5.3.2 "Obtaining an Entity Manager Factory in a Java SE Container" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* [[Introduction%20to%20Java%20Persistence%20API%20(ELUG)#Application-Managed Entity Manager|Application-Managed Entity Manager]]


===How to Obtain an Entity Manager===
All entity managers come from factories of type <tt>EntityManagerFactory</tt>. The configuration for an entity manager is bound to the <tt>EntityManagerFactory</tt> that created it, but it is defined separately as a persistence unit. A persistence unit dictates either implicitly or explicitly the settings and entity classes used by all entity managers obtained from the unique <tt>EntityManagerFactory</tt> instance bound to that persistence unit. There is, therefore, a one-to-one correspondence between a persistence unit and its concrete <tt>EntityManagerFactory</tt>.Persistence units are named to allow differentiation of one <tt>EntityManagerFactory</tt> from another. This gives the application control over which configuration or persistence unit is to be used for operating on a particular entity.

How you obtain the entity manager and its factory depends on the Java environment in which you are developing your application:
* [[#Obtaining an Entity Manager in Java EE Application Server Environment|Obtaining an Entity Manager in Java EE Application Server Environment]]
* [[#Obtaining an Entity Manager in Java SE Environment|Obtaining an Entity Manager in Java SE Environment]]


====Obtaining an Entity Manager in Java EE Application Server Environment====
In the Java EE environment, you can inject an entity manager using the <tt>@PersistenceContext</tt> annotation, as the following example shows, or you can obtain it through a direct JNDI lookup. You may choose to specify the <tt>unitName</tt> element of the <tt>@PersistenceContext</tt> annotation to designate the persistence unit whose factory the container is using (see Section 8.4.2 "PersistenceUnit Annotation" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]). You can also specify the <tt>type</tt> element to indicate whether a transaction-scoped (default) or extended persistence context is to be used (see Section 5.6 "Container-managed Persistence Contexts" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]).
<source lang="java">
 @PersistenceContext
 EntityManager em;
 
 @PersistenceContext(type=PersistenceContextType.EXTENDED)
 EntityManager orderEM;
</source>

The container manages the life cycle of the persistence context, as well as the creation and closing of the entity manager–your application does not have to be involved in this process.

For more information, see the following:
* Section 8.4.2 "PersistenceUnit Annotation" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* Section 5.6 "Container-managed Persistence Contexts" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* Section 5.2.1 "Obtaining an Entity Manager in a Java EE Container" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* [[Introduction%20to%20Java%20Persistence%20API%20(ELUG)#Container-Managed Entity Manage|Container-Managed Entity Manager]]


====Obtaining an Entity Manager in Java SE Environment====
You obtain an application-managed entity manager from an entity manager factory.

For more information and examples, see the following:
* Section 5.2.2 "Obtaining an Entity Manager in a Java SE Container" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* [[#How to Obtain an Entity Manager Factory|How to Obtain an Entity Manager Factory]]
* [[Introduction%20to%20Java%20Persistence%20API%20(ELUG)#Application-Managed Entity Manager|Application-Managed Entity Manager]]


===What You May Need to Know About Entity Managers and Their Factories===
An entity manager persists and manages specific types of objects, enables reading from and writing to a given database. You have to configure the entity manager to do so. You are also responsible for configuring the entity manager to be implemented by a particular persistence provider, such as EclipseLink. The provider supplies the backing implementation engine for the entire Java Persistence API, which includes an entity manager, a <tt>Query</tt> implementation, and SQL generation.

An entity manager implements the API enabling operations on entities. It is encapsulated almost entirely within a single interface called <tt>EntityManager</tt>. Until you use an entity manager to create, read, or write an entity, the entity is nothing more than a regular nonpersistent Java object.

For more information, see Chapter 5 "Entity Managers and Persistence Contexts" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification].

Applications use the <tt>EntityManagerFactory</tt> interface for creating an application-managed entity manager (see [[#Obtaining an Entity Manager in Java SE Environment|Obtaining an Entity Manager in Java SE Environment]]).

Each entity manager factory provides entity manager instances that are all configured in the same manner (for example, configured to connect to the same database or use the same initial settings as defined by the implementation).


===How to Use a Persistence Context===
Information pending


====Using an Extended Persistence Context====
Information pending


===What You May Need to Know About Persistence Contexts and Persistence Units===
When an entity manager (see [[#What You May Need to Know About Entity Managers and Their Factories|What You May Need to Know About Entity Managers and Their Factories]]) obtains a reference to an entity (either by having it explicitly passed in or because it was read from the database) that object becomes managed by the entity manager. The set of managed entity instances within an entity manager at any given time is called this entity manager's persistence context. Only one Java instance with the same persistent identity may exist in a persistence context at any time. For example, if an Employee with a persistent identity (or id) of 158 exists in the persistence context, then no other object with its id set to 158 may exist within that same persistence context.

An <tt>EntityManager</tt> instance is associated with a persistence context. A persistence context is a set of entity instances in which for any persistent entity identity there is a unique entity instance. The entity instances and their life cycle are managed within the persistence context. The <tt>EntityManager</tt> interface defines the methods for interacting with the persistence context. The <tt>EntityManager</tt> API is used to create and remove persistent entity instances, to find entities by their primary key, and to query over entities.

For more information, see Section 5.1 "Persistence Contexts" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification].


====Persistence Unit====
The set of entities that a given <tt>EntityManager</tt> instance manages is defined by a persistence unit. A persistence unit defines the set of all classes that are related or grouped by your application, and which must be collocated in their mapping to a single database.

A persistence unit includes the following:
* An entity manager factory and its entity managers, together with their configuration information.
* The set of classes managed by the entity managers.
* Mapping metadata (in the form of metadata annotations and/or XML metadata) that specifies the mapping of the classes to the database.



==Querying for an Entity==


===How to Use the Entity Manager find Method===

Information pending


===What You May Need to Know About Querying with Java Persistence Query Language===
You can use the Java Persistence query language (JP QL) to define queries over entities and their persistent state.

JP QL is an extension of EJB QL, and adds the following features:

* Single and multiple value result types;
* Aggregate functions with sorting and grouping clauses;
* A more natural jon syntax, including support for both inner and outer joins;
* Conditional expressions involving subqueries;
* Update and delete queries for bulk data changes;
* Result projection into nonpersistent classes.

JP QL supports the use of dynamic queries and the use of named parameters. You can use it to define queries over the persistent entities, as well as their persistent state and relationships

You may define queries in metadata annotations or the XML descriptor.

A JP QL statement may be either a select statement, an update statement, or a delete statement. All statement types may have parameters. Any statement may be constructed dynamically or may be statically defined in a metadata annotation or XML descriptor element.

This example demonstrates how to create a simple query that finds all orders using JP QL.

<span id="Example 21-1"></span>
''''' Simple Query to Find All Objects'''''
<source lang="sql">
 SELECT order
 FROM Order order
</source>

This example demonstrates how to create a simple query that finds all orders to ship to California using JP QL.

<span id="Example 21-2"></span>
''''' Simple Query to Find Some Objects'''''
<source lang="sql">
 SELECT order
 FROM Order order
 WHERE order.shippingAddress.state = 'CA'
</source>

For more information and examples, see the following:

* Chapter 4 "Query Language" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* Section 3.6 "Query API" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* [[#What You May Need to Know About Named and Dynamic Queries|What You May Need to Know About Named and Dynamic Queries]]
* [[#What You May Need to Know About Persisting with JP QL|What You May Need to Know About Persisting with JP QL]]


===What You May Need to Know About Named and Dynamic Queries===
You can use the <tt>Query</tt> API to define both named and dynamic queries.

Named queries are static and expressed in metadata. You can define named queries using JP QL or SQL, scoping their names to the persistence unit.


{| class="Note oac_no_warn" width="80%" border="1" frame="hsides" rules="groups" cellpadding="3" frame="hsides" rules="groups"
| align="left" |
'''Note:''' The query name must be unique within the scope of the persistence unit.
|}


These queries are efficient to execute as the persistence provider can translate JP QL to SQL once, when you application starts, as opposed to every time the query is executed. You define a named query using the <tt>@NamedQuery</tt> annotation (see Section 8.3.1 "NamedQuery Annotation" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]), which you may place on the class definition for any entity. The annotation defines the name of the query, as well as the query text, as this example shows:


<span id="Example 21-3"></span>
''''' Defining a Named Query'''''
<source lang="java">
 @NamedQuery(name="findSalaryForNameAndDepartment",
             query="SELECT e.salary " +
                   "FROM Employee.e " +
                   "WHERE e.department.name = :deptName AND " +
                   "      e.name = :empName")
</source>

Place your named query on the entity class that most directly corresponds to the query result. In the preceding example, that would be the <tt>Employee</tt> entity.

If you need to define more than one named query for a class, place them inside of a <tt>@NamedQueries</tt> annotation (see Section 8.3.1 "NamedQuery Annotation" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]) that accepts an array of <tt>@NamedQuery</tt> annotations, as this example shows:


<span id="Example 21-4"></span>
''''' Defining Multiple Named Queries for an Entity'''''
<source lang="java">
 @NamedQueries({
     @NamedQuery(name="Employee.findAll",
                 query="SELECT e FROM Employee.e"),
     @NamedQuery(name="Employee.findByPrimaryKey",
                 query="SELECT e FROM Employee.e WHERE e.id = :id"),
     @NamedQuery(name="Employee.findByName",
                 query="SELECT e FROM Employee.e WHERE e.name = :name"),
 })
</source>

Because the query string is defined in the annotation, your application cannot alter it at run time. If you need to specify additional criteria, you must do it using query parameters. This example shows how you can use the <tt>createNamedQuery</tt> method of the <tt>EntityManager</tt> to create a named query that requires a query parameter.


<span id="Example 21-5"></span>
<source lang="java">
''''' Creating a Named Query with Parameters'''''
 @PersistenceContext
 public EntityManager em;
 ...
 customers = em.createNamedQuery("findAllCustomersWithName")
               .setParameter("custName", "Smith").getResultList();
</source>

You may choose to define named queries in an XML mapping file (see [[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#Using XML|Using XML]]) using the <tt>named-query</tt> element. A <tt>named-query</tt> element in the mapping file may also override an existing query of the same name that was defined as an annotation. A <tt>named-query</tt> element may appear as a subelement of <tt>entity-mapping</tt> or <tt>entity</tt> elements. Regardless of where you defined it, it will be keyed by its name in the persistence unit query namespace. You may provide [[#What You May Need to Know About Query Hints|query hints]] as <tt>hint</tt> subelements.

This example shows the definition a named query in an XML mapping file. This query uses <tt>eclipselink.cache-usage</tt> hint to bypass the cache.

<span id="Example 21-6"></span>
''''' Defining a Named Query in an XML Mapping File'''''
<source lang="xml">
 <entity-mapping>
     ...
     <named-query name="findEmployeesWithName">
 
         <query>SELECT e FROM Employee e WHERE e.name LIKE :empName</query>
         <hint name="eclipselink.cache-usage" value="DoNotCheckCache"/>
     </named-query>
     ...
 <entity-mapping>
</source>

{| class="Note oac_no_warn" width="80%" border="1" frame="hsides" rules="groups" cellpadding="3" frame="hsides" rules="groups"
| align="left" |
'''Note:''' We recommend using named queries with query parameters.
|}


Dynamic queries are strings. You generate these queries at run time by passing the JP QL query string to the <tt>createQuery</tt> method of the <tt>EntityManager</tt>. There are no restrictions on the query definition; all JP QL query types are supported, as well as the use of parameters.

You may consider using dynamic queries in your application, if there might be a need to specify complex criteria and the exact shape of the query cannot be known in advance. However, note that if your application issues many queries, the use of dynamic queries will have a negative impact on performance.

For more information and examples, see the following:

* Section 3.6.4 "Named Queries" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* Section 3.6 "Query API" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#Using EclipseLink JPA Query Customization Extensions|Using EclipseLink JPA Query Customization Extensions]]
* [[EclipseLink/UserGuide/Caching with EclipseLink (ELUG)#Cache|Cache]]
* [[Introduction%20to%20EclipseLink%20Queries%20(ELUG)#Named Queries|Named Queries]]
* [[#What You May Need to Know About Query Hints|What You May Need to Know About Query Hints]]

==Persisting Domain Model Changes==


===How to Use JTA===

Information pending


===How to Use RESOURCE_LOCAL===

Information pending


===How to Configure Flushing and Set Flush Modes===

Information pending


===How to Manage a Life Cycle of an Entity===

Information pending


====Merging Detached Entity State====

Information pending


====Using Detached Entities and Lazy Loading====

Information pending

For more information, see the following:

* Section 3.2.4.2 "Detached Entities and Lazy Loading" of JPA specification
* [[Introduction%20to%20Mappings%20(ELUG)|Indirection, Serialization, and Detachment]]


===What You May Need to Know About Persisting with JP QL===

You may define queries in metadata annotations or the XML descriptor.

You can use update and delete queries to persist your changes with JP QL.

You can perform bulk update of entities with the <tt>UPDATE</tt> statement. This statement operates on a single entity type and sets one or more single-valued properties of the entity subject to the condition in the <tt>WHERE</tt> clause. Update queries provide an equivalent to the <tt>SQL UPDATE</tt> statement, but with JP QL conditional expressions.

This example demonstrates how to use an update query to give employees a raise. The <tt>WHERE</tt> clause contains the conditional expression.

<span id="Example 21-7"></span>
'''''Update Query'''''
<source lang="sql">
 UPDATE Employee e
 SET e.salary = 60000
 WHERE e.salary = 50000
</source>

You can perform bulk removal of entities with the <tt>DELETE</tt> statement. Delete queries provide an equivalent to the <tt>SQL DELETE</tt> statement, but with JP QL conditional expressions.

This example demonstrates how to use a delete query to remove all employees who are not assigned to a department. The <tt>WHERE</tt> clause contains the conditional expression.

<span id="Example 21-8"></span>
''''' Delete Query'''''
<source lang="sql">
 DELETE FROM Employee e
 WHERE e.department IS NULL
</source>

{| class="Note oac_no_warn" width="80%" border="1" frame="hsides" rules="groups" cellpadding="3" frame="hsides" rules="groups"
| align="left" |
'''Note:''' Delete queries are polymorphic: any entity subclass instances that meet the criteria of the delete query will be deleted. However, delete queries do not honor cascade rules: no entities other than the type referenced in the query and its subclasses will be removed, even if the entity has relationships to other entities with cascade removes enabled.
|}


The persistence context is not updated to reflect results of update and delete operations. If you use a transaction-scoped persistence context, you should either execute the bulk operation in a transaction all by itself, or be the first operation in the transaction (see [[Introduction%20to%20EclipseLink%20Transactions (ELUG)|Introduction to EclipseLink Transactions]]). That is because any entity actively managed by the persistence context will remain unaware of the actual changes occurring at the database level.

For more information and examples, see the following:

* Section 4.10 "Bulk Update and Delete Operations" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* Chapter 4 "Query Language" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* [[#What You May Need to Know About Querying with Java Persistence Query Language|What You May Need to Know About Querying with Java Persistence Query Language]]
* [[EclipseLink/UserGuide/Queries (ELUG)|Queries]]
* [[Introduction%20to%20EclipseLink%20Queries%20(ELUG)#Named Queries|Named Queries]]


===What You May Need to Know About Persisting Results of Named and Dynamic Queries===

Expressions listed in the <tt>SELECT</tt> clause of a query determine the result type of the query. The following are some of the type that may result from JP QL queries:

* Basic types: <tt>String</tt>, primitive types, JDBC types
* Entity types
* An array of <tt>Object</tt> instances
* User-defined types created from a constructor-expressions

The collection or single result corresponds directly to the result type of the query.

The <tt>Query</tt> interface provides three different ways to execute a query, depending on whether or not the query returns results and how many results are expected. For queries that return values, you can call either the following methods:

* <tt>getResultList</tt>–use this method if you expect the query to return more than one result. This method returns a collection (<tt>List</tt>) containing query results. If there are no results to return, this method returns an empty collection.
* <tt>getSingleResult</tt>–use this method if you expect the query to return a single result. In case of unexpected results, such as there are no results to return or multiple results are available, this method throws an exception.

Use the <tt>executeUpdate</tt> method of the <tt>Query</tt> interface to invoke bulk update and delete queries (see [[#What You May Need to Know About Persisting with JP QL|What You May Need to Know About Persisting with JP QL]]).

The active persistence context manages a returned entity instance. If that entity instance is modified and the persistence context is part of a transaction, then the changes will be persisted to the database.


{| class="Note oac_no_warn" width="80%" border="1" frame="hsides" rules="groups" cellpadding="3" frame="hsides" rules="groups"
| align="left" |
'''Note:''' If you use a transaction-scoped entity manager outside of a transaction, then the executed query will return detached entity instances instead of managed entity instances. To make changes to these detached entities, you must merge them into a persistence context before synchronizing with the database.
|}


You can reuse <tt>Query</tt> objects as often as you need so long as the same persistence context that you used to create the query is active. For transaction-scoped entity managers, this limits the lifetime of the <tt>Query</tt> object to the life of the transaction. Other entity manager types may reuse <tt>Query</tt> objects until you close or remove the entity manager.

For more information, see the following:
* Section 3.6 "Query API" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* Section 3.6.4 "Named Queries" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#Using EclipseLink JPA Query Customization Extensions|Using EclipseLink JPA Query Customization Extensions]]
* [[EclipseLink/UserGuide/Queries (ELUG)|Queries]]
* [[Introduction%20to%20EclipseLink%20Queries%20(ELUG)#Named Queries|Named Queries]]
* Section 5.6.4.1 "Container-managed Transaction-scoped Persistence Context" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]


==Using EclipseLink JPA Extensions in Your Application Development==
This section describes the following:
* [[#How to Use Extensions for Query|How to Use Extensions for Query]]
* [[#How to Configure Lazy Loading|How to Configure Lazy Loading]]
* [[#How to Configure Change Tracking|How to Configure Change Tracking]]
* [[#How to Configure Fetch Groups|How to Configure Fetch Groups]]
* [[#How to Use Extensions for Caching|What You May Need to Know About EclipseLink Caching]]
* [[#What You May Need to Know About EclipseLink Caching|What You May Need to Know About EclipseLink Caching]]
* [[#What You May Need to Know About Cache Coordination|What You May Need to Know About Cache Coordination]]
* [[#How to Configure Cascading|How to Configure Cascading]]
* [[#What You May Need to Know About Cascading Entity Manager Operations|What You May Need to Know About Cascading Entity Manager Operations]]
* [[#How to Use EclipseLink Metadata|How to Use EclipseLink Metadata]]
* [[#How to Use Events and Listeners|How to Use Events and Listeners]]
* [[#What You May Need to Know About Database Platforms|What You May Need to Know About Database Platforms]]
* [[#What You May Need to Know About Server Platforms|What You May Need to Know About Server Platforms]]
* [[#How to Optimize a JPA Application|How to Optimize a JPA Application]]
* [[#How to Perform Diagnostics|How to Perform Diagnostics]]


===How to Use Extensions for Query===
Information pending


====Using Query Hints====

Information pending


====What You May Need to Know About Query Hints====
Query hints are the JPA extension point for vendor-specific query features. Hints are the only feature in the query API that are not a standard usage: a hint is a string name and object value.

You may associate your queries with hints by either setting them in the persistence unit metadata as part of the <tt>@NamedQuery</tt> annotation (see Section 8.3.1 "NamedQuery Annotation" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]), or by using the <tt>setHint</tt> method of the <tt>Query</tt>.

The [[#Example 21-9| Using Query Hints]] example shows how to use the <tt>eclipselink.cache-usage</tt> hint to indicate that the cache should not be checked when reading an <tt>Employee</tt> for the database.


{| class="Note oac_no_warn" width="80%" border="1" frame="hsides" rules="groups" cellpadding="3" frame="hsides" rules="groups"
| align="left" |
'''Note:''' Unlike the <tt>refresh</tt> method of the <tt>EntityManager</tt>, the <tt>eclipselink.cache-usage</tt> hint will not cause the query result to override the current cached value.
|}


<span id="Example 21-9"></span>
''''' Using Query Hints'''''
<source lang="java">
 public Employee findEmployeeNoCache(int empId) {
     Query q = em.createQuery("SELECT e FROM Employee e WHERE e.id = ?1");
     // force read from database
     q.setHint("eclipselink.cache-usage", "DoNotCheckCache");
     q.setParameter(1, empId);
     try {
         return (Employee)q.getSingleResult();
     }
     catch(NoResultException e) {
         return null;
     }
 }
</source>

If you need execute this query frequently, you should use a named query. The following named query definition incorporates the cache hint from the [[#Example 21-9| Using Query Hints]] example.
 @NamedQuery(name="findEmployeeNoCache",
             query="SELECT e FROM Employee e WHERE e.id = :empId",
             hints={@QueryHint(name="eclipselink.cache-usage", 
                               value="DoNotCheckCache")})

The <tt>hints</tt> element accepts an array of <tt>@QueryHint</tt> annotations (see Section 8.3 "Annotations for Queries" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]), allowing you to set any number of hints for a query.

For more information, see the following:
* Section 3.6 "Query API" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#Using EclipseLink JPA Query Customization Extensions|Using EclipseLink JPA Query Customization Extensions]]
* [[EclipseLink/UserGuide/Caching with EclipseLink (ELUG)#Cache|Cache]]
* [[Using%20Advanced%20Query%20API%20(ELUG)#How to Use Oracle Hints|How to Use Oracle Hints]]

====Using the Expression API====
Information pending


===How to Configure Lazy Loading===
By default, the EclipseLink persistence provider will use dynamic weaving to configure all applicable mappings with lazy loading (indirection).

For JPA entities or POJO classes that you configure for weaving, EclipseLink weaves value holder indirection for one-to-one mappings. If you want EclipseLink to weave change tracking and your application includes collection mappings (one-to-many and many-to-many), then you must configure all collection mappings to use transparent indirect container indirection only (you may not configure your collection mappings to use eager loading, nor value holder indirection).

For more information, see the following:
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)|Using EclipseLink JPA Extensions for Customization and Optimization]]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)|What You May Need to Know About EclipseLink JPA Lazy Loading]]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)|Using EclipseLink JPA Weaving]]
* [[Configuring%20a%20Mapping%20(ELUG)|Configuring Indirection (Lazy Loading)]]


===How to Configure Change Tracking===
By default, the EclipseLink persistence provider will use dynamic weaving to configure all applicable mappings with attribute level change tracking.

For JPA entities or POJO classes that you configure for weaving, EclipseLink weaves value holder indirection for one-to-one mappings. If you want EclipseLink to weave change tracking and your application includes collection mappings (one-to-many and many-to-many), then you must configure all collection mappings to use transparent indirect container indirection only (you may not configure your collection mappings to use eager loading, nor value holder indirection).

For more information, see the following:
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#Using EclipseLink JPA Extensions for Tracking Changes|Using EclipseLink JPA Extensions for Tracking Changes]]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#Using EclipseLink JPA Weaving|Using EclipseLink JPA Weaving]]
* [[Configuring%20a%20Descriptor%20(ELUG)#Configuring Change Policy|Configuring Change Policy]]


===How to Configure Fetch Groups===
By default, the EclipseLink persistence provider will use dynamic weaving to configure all applicable mappings to use fetch groups.

For more information, see the following:
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)|Using EclipseLink JPA Extensions for Customization and Optimization]]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)|Using EclipseLink JPA Weaving]]
* [[Configuring%20a%20Descriptor%20(ELUG)#Configuring Fetch Groups|Configuring Fetch Groups]]


===How to Use Extensions for Caching===

Information pending


===What You May Need to Know About EclipseLink Caching===
The EclipseLink cache is an in-memory repository that stores recently read or written objects based on class and primary key values. EclipseLink uses the cache to do the following:
* Improve performance by holding recently read or written objects and accessing them in-memory to minimize database access.
* Manage locking and isolation level.
* Manage object identity.

EclipseLink uses the following two types of cache:
* the session cache maintains objects retrieved from and written to the data source;
* the unit of work cache holds objects while they participate in transactions.

When a unit of work successfully commits to the data source, EclipseLink updates the session cache accordingly.

For more information, see [[EclipseLink/UserGuide/Caching with EclipseLink (ELUG)|Cache]].


===What You May Need to Know About Cache Coordination===
EclipseLink provides a distributed cache coordination feature that ensures data in distributed applications remains current.

For more information, see the following:
* [[Introduction%20to%20Cache%20(ELUG)#Cache Coordination|Cache Coordination]]
* [[Configuring%20a%20Descriptor%20(ELUG)#Configuring Locking Policy)|Configuring Locking Policy]]
* [[Introduction%20to%20Cache%20(ELUG)#Querying and the Cache|Querying and the Cache]]
* [[EclipseLink/UserGuide/Queries (ELUG)|Cache]]


===How to Configure Cascading===

Information pending

For more information, see the following:
* [[#What You May Need to Know About Cascading Entity Manager Operations|What You May Need to Know About Cascading Entity Manager Operations]]
* [[Introduction%20to%20EclipseLink%20JPA%20(ELUG)|Mapping Relationships]]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)|Using EclipseLink JPA Extensions for Optimistic Locking]]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)|How to Use the @PrivateOwned Annotation]]


===What You May Need to Know About Cascading Entity Manager Operations===
Typically, you use cascading in parent-child relationships.

By default, every entity manager operation applies only to the entity that you supplied as an argument to the operation. The operation will not cascade to other entities that have a relationship with the entity under operation. For some operations, such as <tt>remove</tt>, this is usually the desired behavior. For other operations, such as <tt>persist</tt>, it is not: in most cases, if you have a new entity that has a relationship to another new entity, you would want to persist both entities together.

Using the <tt>cascade</tt> element of relationship annotations (see [[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#Mapping Relationships|Mapping Relationships]]), you can define whether or not to cascade operations across relationships.

When listed as a part of the <tt>cascade</tt> element, you can identify the entity manager operations with the following constant values using the <tt>javax.persitence.CascadeType</tt> enumerated type:
* <tt>PERSIST</tt>–corresponds to the entity manager <tt>persist</tt> operation;
* <tt>REFRESH</tt>–corresponds to the entity manager <tt>refresh</tt> operation;
* <tt>REMOVE</tt>–corresponds to the entity manager <tt>remove</tt> operation;
* <tt>MERGE</tt>–corresponds to the entity manager <tt>merge</tt> operation;
* <tt>ALL</tt>–indicates that all four operations should be cascaded.


{| class="Note oac_no_warn" width="80%" border="1" frame="hsides" rules="groups" cellpadding="3" frame="hsides" rules="groups"
| align="left" |
'''Note:''' Cascade sessions are unidirectional: you must set them on both sides of a relationship if you plan for the same behavior for both situations.
|}


For more information, see the following:
* [[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#Mapping Relationships|Mapping Relationships]]
* [[#How to Configure Cascading|How to Configure Cascading]]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#How to Use the @OptimisticLocking Annotation|How to Use the @OptimisticLocking Annotation]]
* [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#How to Use the @PrivateOwned Annotation|How to Use the @PrivateOwned Annotation]]


===How to Use EclipseLink Metadata===

Information pending


====Using EclipseLink Project====

Information pending


====Using sessions.xml File====

Information pending


===How to Use Events and Listeners===

Information pending

<org.eclipse.persistence.sessions.SessionEventListener (eclipselink.session.event-listener)>

<Configure a descriptor event listener to be added during bootstrap.>


====Using Session Events====

Information pending


====Using an Exception Handler====

Information pending


===What You May Need to Know About Database Platforms===
EclipseLink interacts with databases using SQL. The type of database platform you choose determines the specific means by which the EclipseLink runtime accesses the database.

For more information, see [[Introduction%20to%20Data%20Access%20(ELUG)#Database Platforms|Database Platforms]].


===What You May Need to Know About Server Platforms===
You deploy your application to a specific Java EE application server.

EclipseLink supports most versions of WebLogic, OC4J, SunAS, and WebSphere application servers.

For more information, see the following:

* [[Configuring%20a%20Session%20(ELUG)#Configuring the Server Platform|Configuring the Server Platform]]
* [[Integrating%20EclipseLink%20with%20an%20Application%20Server%20(ELUG)|Integrating EclipseLink with an Application Server]]

===How to Optimize a JPA Application===

Information pending


====Using Statement Caching====

Information pending


====Using Batch Reading and Writing====

Information pending


===How to Perform Diagnostics===

Information pending


====Using Logging====

Information pending


====Using Profiling====

Information pending


====Using JMX====

Information pending




----
''[[EclipseLink User's Guide Copyright Statement|Copyright Statement]]''


[[Category: EclipseLink User's Guide]]
[[Category: Release 1]]
[[Category: Task]]
[[Category: JPA]]
Return to Developing Applications Using EclipseLink JPA (ELUG).
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