Examples of FetchGroup

javax.jdo.FetchGroup
FetchGroup represents a named fetch group for a specific class or interface. A fetch group instance identifies the name of the class or interface, the list of members (fields or properties) to be fetched when the fetch group is active, and the recursion depth for each member.
Fetch groups are updated using methods on this interface. An instance of a class implementing this interface can be obtained from {@link PersistenceManager#getFetchGroup} or{@link PersistenceManagerFactory#getFetchGroup}.
A FetchGroup can be unscoped or can be in one of two scopes (the {@link PersistenceManager} or the {@link PersistenceManagerFactory} scope). Unscoped FetchGroups do not affect any behavior. A FetchGroup in PersistenceManager scope hides the corresponding FetchGroup in the PersistenceManagerFactory scope.
- When a FetchGroup is obtained via {@link PersistenceManager#getFetchGroup}, it is immediately in scope of its PersistenceManager. Subsequent modifications of the FetchGroup immediately affect FetchPlans that contain the FetchGroup.
- When a FetchGroup is obtained via {@link PersistenceManagerFactory#getFetchGroup}, it is unscoped.
- When a FetchGroup is added to the set of active FetchGroups via {@link PersistenceManagerFactory#addFetchGroups}, it is put in scope of the PersistenceManagerFactory.
- When a FetchGroup is removed from the set of active FetchGroups via {@link PersistenceManagerFactory#removeFetchGroups}, {@link PersistenceManagerFactory#removeAllFetchGroups}, or replaced via {@link PersistenceManagerFactory#addFetchGroups}, it is unscoped.
@version 2.2 @since 2.2
oracle.toplink.essentials.queryframework.FetchGroup

Purpose: A fetch group is a performance enhancement that allows a group of attributes of an object to be loaded on demand, which means that the data for an attribute might not loaded from the underlying data source until an explicit access call for the attribute first occurs. It avoids the wasteful practice of loading up all data of the object?s attributes, in which the user is interested in only partial of them. A great deal of caution and careful system use case analysis should be use when using the fetch group feature, as the extra round-trip would well offset the gain from the deferred loading in many cases. TopLink fetch group support is twofold: the pre-defined fetch groups at the descriptor level; and dynamic (use case) fetch groups at the query level. TopLink fetch group support is only on CMP project. Every query can has at most one fetch group. There is an optional pre-defined default fetch group at the descriptor level. If set, and the query has no fetch group being set, the default fetch group would be used, unless query.setShouldUseDefaultFetchGroup(false) is also called. In the latter case, the full object will be fetched after the query execution. @see oracle.toplink.essentials.queryframework.FetchGroup @see oracle.toplink.essentials.queryframework.FetchGroupTracker @author King Wang @since TopLink 10.1.3.
org.apache.james.mailbox.MessageResult.FetchGroup
org.apache.james.mailbox.model.MessageResult.FetchGroup
org.apache.openjpa.meta.FetchGroup
Captures fetch group metadata.
org.datanucleus.FetchGroup
Group of fields for fetching, to be part of a FetchPlan. Defined at runtime, via the API.
org.eclipse.persistence.queries.FetchGroup
A FetchGroup is a performance enhancement that allows a group of attributes of an object to be loaded on demand, which means that the data for an attribute might not loaded from the underlying data source until an explicit access call for the attribute first occurs. It avoids loading all data of the object's attributes, in which the user is interested in only a subset of them. A great deal of caution and careful system use case analysis should be use when using the fetch group feature, as the extra round-trip would well offset the gain from the deferred loading in many cases.
FetchGroup usage is only possible when an entity class implements the {@link FetchGroupTracker} interface so that the FetchGroup can be stored inthe entity. The entity must also use the provided check methods to ensure the attributes are loaded prior to use. In general this support is enabled through weaving of the entity classes. If an entity class does not implement {@link FetchGroupTracker} no FetchGroup functionality will be supported andattempted use of a FetchGroup in a query will not result in the expected behavior.
FetchGroups are defined in 3 ways:
- A {@link FetchGroupManager#getDefaultFetchGroup()} is created and storedon the {@link FetchGroupManager} during metadata processing if any of thebasic ( {@link DirectToFieldMapping}) are configured to be loaded directly.
- A named FetchGroup can be defined and added to the {@link FetchGroupManager}. For JPA users this can be accomplished using annotation (@FetchGroup) or in an eclipselink-orm.xml. For JPA and native users named groups can be defined in code and added to the {@link FetchGroupManager#addFetchGroup(FetchGroup)}. Adding named groups in code is typically done in a {@link DescriptorCustomizer}and should be done before the session is initialized at login. To use a named FetchGroup on a query the native {@link ObjectLevelReadQuery#setFetchGroupName(String)} canbe used of for JPA users the {@link QueryHints#FETCH_GROUP_NAME} an be used.
- A dynamic FetchGroup can be created within the application and used on a query. For native API usage this is done using {@link ObjectLevelReadQuery#setFetchGroup(FetchGroup)} while JPA usersgenerally use the {@link QueryHints#FETCH_GROUP}.
When a query is executed only one FetchGroup will be used. The order of precedence is:
1. If a FetchGroup is specified on a query it will be used.
2. If no FetchGroup is specified but a FetchGroup name is specified and the FetchGroupManager has a group by this name it will be used.
3. If neither a FetchGroup nor a FetchGroup name is specified on the query an the FetchGroupManager has a default group then it will be used.
4. If none of these conditions are met then no FetchGroup will be used when executing a query.
  Note: This includes the execution of queries to populate lazy and eager relationships.
  Loading: A FetchGroup can optionally specify that it needs its included relationships loaded. This can be done using {@link #setShouldLoad(boolean)} and {@link #setShouldLoadAll(boolean)} aswell as the corresponding configurations in the @FetchGroup annotation and the element in the eclipselink-orm.xml. When this si configured the FetchGroup will also function as a {@link LoadGroup} causing all of itsspecified relationships to be populated prior to returning the results form the query execution. @see FetchGroupManager @see QueryHints#FETCH_GROUP @see LoadGroup @author King Wang, dclarke, ailitchev @since TopLink 10.1.3

Examples of org.eclipse.persistence.queries.FetchGroup

316 317 318 319 320 321 322 323 /** * Return true if the attribute of the object has already been fetched */ public boolean isAttributeFetched(Object object, String attributeName) { FetchGroup fetchgroup = ((FetchGroupTracker)object)._persistence_getFetchGroup(); return (fetchgroup == null) || (fetchgroup.containsAttribute(attributeName)); }

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Examples of org.eclipse.persistence.queries.FetchGroup

392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 //to use fetch group, the domain class must implement FetchGroupTracker interface session.getIntegrityChecker().handleError(DescriptorException.needToImplementFetchGroupTracker(getDescriptor().getJavaClass(), getDescriptor())); } if (getDefaultFetchGroup() == null) { // Check for lazy mappings to build default fetch group. FetchGroup fetchGroup = new FetchGroup(); boolean hasLazy = false; for (DatabaseMapping mapping : getDescriptor().getMappings()) { if (mapping.isForeignReferenceMapping() || (!mapping.isLazy())) { fetchGroup.addAttribute(mapping.getAttributeName()); } else { hasLazy = true; } } if (hasLazy) {

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