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 javax.jdo.FetchGroup

454 455 456 457 458 459 460 461 462 463 464         }     }     public void testPMFGetFetchGroupClassNotPersistenceCapable() {         try {             FetchGroup fg = pmf.getFetchGroup(Integer.class, "testtestPMFGetFetchGroupClassNotPersistenceCapableGetFetchGroupClassNotPersistenceCapable");             fail("getFetchGroup should throw on nonPersistenceCapable class.");         } catch(JDOException ex) {             // good catch!         }     }

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Examples of javax.jdo.FetchGroup

463 464 465 466 467 468 469 470 471 472 473         }     }     public void testPMFGetFetchGroupInterfaceNotPersistenceCapable() {         try {             FetchGroup fg = pmf.getFetchGroup(IEmployee.class, "testPMFGetFetchGroupInterfaceNotPersistenceCapable");             fail("getFetchGroup should throw on nonPersistenceCapable interface.");         } catch(JDOException ex) {             // good catch!         }     }

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Examples of javax.jdo.FetchGroup

471 472 473 474 475 476 477 478 479 480 481 482 483             // good catch!         }     }     public void testAddMemberNotAMember() {         FetchGroup fg = pm.getFetchGroup(Employee.class, "testAddMemberNotAMember");         try {             fg.addMember("NotAMember");             fail("FetchGroup should throw on addMember(NotAMember).");         } catch(JDOException ex) {             // good catch!         }     }

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Examples of javax.jdo.FetchGroup

481 482 483 484 485 486 487 488 489 490 491 492 493             // good catch!         }     }     public void testAddMembersNotAMember() {         FetchGroup fg = pm.getFetchGroup(Employee.class, "testAddMembersNotAMember");         try {             fg.addMembers(new String[]{"NotAMember"});             fail("FetchGroup should throw on addMembers(NotAMember).");         } catch(JDOException ex) {             // good catch!         }     }

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Examples of javax.jdo.FetchGroup

491 492 493 494 495 496 497 498 499 500 501 502 503 504             // good catch!         }     }     public void testRemoveMemberNotAMember() {         FetchGroup fg = pm.getFetchGroup(Employee.class, "testRemoveMemberNotAMember");         fg.addCategory(FetchGroup.ALL);         try {             fg.removeMember("NotAMember");             fail("FetchGroup should throw on removeMember(NotAMember).");         } catch(JDOException ex) {             // good catch!         }     }

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Examples of javax.jdo.FetchGroup

502 503 504 505 506 507 508 509 510 511 512 513 514 515             // good catch!         }     }     public void testRemoveMembersNotAMember() {         FetchGroup fg = pm.getFetchGroup(Employee.class, "testRemoveMembersNotAMember");         fg.addCategory(FetchGroup.ALL);         try {             fg.removeMembers(new String[]{"NotAMember"});             fail("FetchGroup should throw on removeMembers(NotAMember).");         } catch(JDOException ex) {             // good catch!         }     }

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Examples of javax.jdo.FetchGroup

513 514 515 516 517 518 519 520 521 522 523 524 525             // good catch!         }     }     public void testSetRecursionDepthNotAMember() {         FetchGroup fg = pm.getFetchGroup(Employee.class, "testSetRecursionDepthNotAMember");         try {             fg.setRecursionDepth("NotAMember", 64);             fail("FetchGroup should throw on setRecursionDepth(NotAMember).");         } catch(JDOException ex) {             // good catch!         }     }

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Examples of javax.jdo.FetchGroup

523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541             // good catch!         }     }     private void checkAddCategory(Class cls, String category, String[] expected) {         FetchGroup fg = pm.getFetchGroup(cls, "test" + count() + category);         Set expectedSet = new HashSet();         expectedSet.addAll(Arrays.asList(expected));         Set members = fg.getMembers();         assertTrue("New FetchGroup should have no members; "                 + printFetchGroup(fg),                 members.isEmpty());         fg.addCategory(category);         members = fg.getMembers();         if (!members.equals(expectedSet)) {             appendMessage("FetchGroup(" + cls.getName()                     + ".addCategory(" + category + ") should contain\n"                 + expectedSet + " but contains\n" + members);         }

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Examples of javax.jdo.FetchGroup

162 163 164 165 166 167 168 169 170 171 172 173                     + "Expected: " + expected + " actual: " + actual,                     actual, expected);     }     public void testPMGetFetchGroupIdentical() {         FetchGroup scoped = pm.getFetchGroup(Address.class, "default");         FetchGroup identical = pm.getFetchGroup(Address.class, "default");         assertSame("Modifiable FetchGroup is not identical to modifiable FetchGroup;"                     + "FetchGroup: " + printFetchGroup(scoped)                     + " identical: " + printFetchGroup(identical),                     scoped, identical);     }

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Examples of javax.jdo.FetchGroup

171 172 173 174 175 176 177 178 179 180 181 182 183                     + " identical: " + printFetchGroup(identical),                     scoped, identical);     }     public void testPMGetFetchGroupUnmodifiableNotIdentical() {         FetchGroup scoped = pm.getFetchGroup(Address.class, "default");         scoped.setUnmodifiable();         FetchGroup modifiable = pm.getFetchGroup(Address.class, "default");         assertNotSame("Unmodifiable FetchGroup is identical to modifiable FetchGroup;"                     + "\nunmodifiable: " + printFetchGroup(scoped)                     + "\n modifiable: " + printFetchGroup(modifiable),                     scoped, modifiable);     }

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