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Inherits from: Object
Implements: Serializable
Package: com.webobjects.eocontrol
The EOClassDescription class provides a mechanism for extending classes by giving them access to metadata not available in the run-time system. This is achieved as follows:
Enterprise Objects Framework implements a default subclass of EOClassDescription in EOAccess, EOEntityClassDescription. EOEntityClassDescription extends the behavior of enterprise objects by deriving information about them (such as NULL constraints and referential integrity rules) from an associated EOModel.
For more information on using EOClassDescription, see the sections
EOClassDescription defines the following int constants:
EOClassDescription also defines string constants for the names of the notifications it posts. For more information, see the section "Notifications" (page 54).
Managing EOClassDescriptions
invalidateClassDescriptionCacheregisterClassDescriptionGetting EOClassDescriptions
classDescriptionForClassclassDescriptionForEntityNameCreating new object instances
createInstanceWithEditingContextPropagating delete
propagateDeleteForObjectReturning information from the EOClassDescription
entityName
attributeKeys
classDescriptionForDestinationKey
toManyRelationshipKeys
toOneRelationshipKeys
inverseForRelationshipKey
ownsDestinationObjectsForRelationshipKey
deleteRuleForRelationshipKeyPerforming validation
validateObjectForDeletevalidateObjectForSavevalidateValueForKeyProviding default characteristics for key display
defaultFormatterForKeydefaultFormatterForKeyPathdisplayNameForKeyHandling newly inserted and newly fetched objects
awakeObjectFromFetchawakeObjectFromInsertionSetting the delegate
classDelegatesetClassDelegateGetting an object's description
userPresentableDescriptionForObjectGetting fetch specifications
fetchSpecificationNamed
public static Object classDelegate()
Returns the delegate for the EOClassDescription class (as opposed to EOClassDescription instances).
See Also: setClassDelegate
public static EOClassDescription classDescriptionForClass(Class aClass)
Invoked by the default implementations of the EOEnterpriseObject interface method classDescription to return the EOClassDescription for aClass. It's generally not safe to use this method directly-for example, individual EOGenericRecord instances can have different class descriptions. If a class description for aClass isn't found, this method posts an ClassDescriptionNeededForClassNotification on behalf of the receiver's class, allowing an observer to register a an EOClassDescription.
public static EOClassDescription classDescriptionForEntityName(String entityName)
Returns the EOClassDescription registered under entityName.
public static void invalidateClassDescriptionCache()
Flushes the EOClassDescription cache. Because the EOModel objects in an application supply and register EOClassDescriptions on demand, the cache continues to be repopulated as needed after you invalidate it. (The EOModel class is defined in EOAccess.)
You'd use this method when a provider of EOClassDescriptions (such as an EOModel) has newly become available, or is about to go away. However, you should rarely need to directly invoke this method unless you're using an external source of information other than an EOModel.
public static void registerClassDescription( EOClassDescription description, Class class)
Registers an EOClassDescription object for class in the EOClassDescription cache. You should rarely need to directly invoke this method unless you're using an external source of information other than an EOModel (EOAccess).
public static void setClassDelegate(Object delegate)
Sets the delegate for the EOClassDescription class (as opposed to EOClassDescription instances) to delegate. For more information on the class delegate, see the EOClassDescription.ClassDelegate interface specification.
See Also: classDelegate
public NSArray attributeKeys()
Overridden by subclasses to return an array of attribute keys (Strings) for objects described by the receiver. "Attributes" contain immutable data (such as Numbers and Strings), as opposed to "relationships" that are references to other enterprise objects. For example, a class description that describes Movie objects could return the attribute keys "title," "dateReleased," and "rating."
EOClassDescription's implementation of this method simply returns.
See Also: entityName, toOneRelationshipKeys, toManyRelationshipKeys
public void awakeObjectFromFetch( EOEnterpriseObject object, EOEditingContext anEditingContext)
Overridden by subclasses to perform standard post-fetch initialization for object in anEditingContext. EOClassDescription's implementation of this method does nothing.
public void awakeObjectFromInsertion( EOEnterpriseObject object, EOEditingContext anEditingContext)
Assigns empty arrays to to-many relationship properties of newly inserted enterprise objects. Can be overridden by subclasses to propagate inserts for the newly inserted object in anEditingContext. More specifically, if object has a relationship (or relationships) that propagates the object's primary key and if no object yet exists at the destination of that relationship, subclasses should create the new object at the destination of the relationship. Use this method to put default values in your enterprise object.
public EOClassDescription classDescriptionForDestinationKey(String detailKey)
Overridden by subclasses to return the class description for objects at the destination of the to-one relationship identified by detailKey. For example, the statement:
movie.classDescriptionForDestinationKey("studio")
might return the class description for the Studio class. EOClassDescription's implementation of this method returns null.
public NSArray clientAttributeKeys()
Returns an array containing the names of the attributes that are bound to the client-side class that corresponds to the receiver's entity.
public NSArray clientToManyRelationshipKeys()
Returns an array containing the names of the to-many relationships that are bound to the client-side class that corresponds to the receiver's entity.
public NSArray clientToOneRelationshipKeys()
Returns an array containing the names of the to-one relationships that are bound to the client-side class that corresponds to the receiver's entity.
public EOEnterpriseObject createInstanceWithEditingContext( EOEditingContext anEditingContext, EOGlobalID globalID)
Overridden by subclasses to create an object of the appropriate class in anEditingContext with globalID. In typical usage, both of the method's arguments are null. To create the object, the subclass should pass anEditingContext, itself, and globalID to the appropriate constructor. Implementations of this method should return an autoreleased object. Enterprise Objects Framework uses this method to create new instances of objects when fetching existing enterprise objects or inserting new ones in an interface layer EODisplayGroup. EOClassDescription's implementation of this method returns null.
public java.text.Format defaultFormatterForKey(String key)
Returns the default NSFormatter to use when parsing values for assignment to key. EOClassDescription's implementation returns null. The access layer's EOEntityClassDescription's implementation returns an NSFormatter based on the Java value class specified for key in the associated model file. Code that creates a user interface, like a wizard, can use this method to assign formatters to user interface elements.
public java.text.Format defaultFormatterForKeyPath(String key)
Similar to defaultFormatterForKey, except this method traverses keyPath and returns the formatter for the key at the end of the path (using defaultFormatterForKey).
public int deleteRuleForRelationshipKey(String relationshipKey)
Overridden by subclasses to return a delete rule indicating how to treat the destination of the given relationship when the receiving object is deleted. The delete rule is one of:
EOClassDescription's implementation of this method returns the delete rule EODeleteRuleNullify. In the common case, the delete rule for an enterprise object is defined in its EOModel. (The EOModel class is defined in EOAccess.)
See Also: propagateDeleteWithEditingContext (EOEnterpriseObject)
public String displayNameForKey(String key)
Returns the default string to use in the user interface when displaying key. By convention, lowercase words are capitalized (for example, "revenue" becomes "Revenue"), and spaces are inserted into words with mixed case (for example, "firstName" becomes "First Name"). This method is useful if you're creating a user interface from only a class description, such as with a wizard or a Direct To Web application.
public String entityName()
Overridden by subclasses to return a unique type name for objects of this class. For example, the access layer's EOEntityClassDescription returns its EOEntity's name. EOClassDescription's implementation of this method returns null.
See Also: attributeKeys, toOneRelationshipKeys, toManyRelationshipKeys
public EOFetchSpecification fetchSpecificationNamed(String name)
Overridden by subclasses to return the fetch specification associated with name. For example, the access layer's EOEntityClassDescription returns the fetch specification in its EOEntity named name (if any). EOClassDescription's implementation returns nil.
public void finalize() throws Throwable
Description forthcoming.
public String inverseForRelationshipKey(String relationshipKey)
Overridden by subclasses to return the name of the relationship pointing back at the receiver from the destination of the relationship specified by relationshipKey. For example, suppose an Employee object has a relationship called department to a Department object, and Department has a relationship called employees back to Employee. The statement:
employee.inverseForRelationshipKey("department");
returns the string "employees".
EOClassDescription's implementation of this method returns null.
public boolean ownsDestinationObjectsForRelationshipKey(String relationshipKey)
Overridden by subclasses to return true or false to indicate whether the objects at the destination of the relationship specified by relationshipKey should be deleted if they are removed from the relationship (and not transferred to the corresponding relationship of another object). For example, an Invoice object owns its line items. If a LineItem object is removed from an Invoice it should be deleted since it can't exist outside of an Invoice. EOClassDescription's implementation of this method returns false.In the common case, this behavior for an enterprise object is defined in its EOModel. (The EOModel class is defined in EOAccess.)
public void propagateDeleteForObject( EOEnterpriseObject object, EOEditingContext anEditingContext)
Propagates a delete operation for object in anEditingContext, according to the delete rules specified in the EOModel. This method is invoked whenever a delete operation needs to be propagated, as indicated by the delete rule specified for the corresponding EOEntity's relationship key. (The EOModel and EOEntity classes are defined in EOAccess.) For more discussion of delete rules, see the EOEnterpriseObject interface specification.
See Also: deleteRuleForRelationshipKey
public EOClassDescription superClassDescription()
Description forthcoming.
public NSArray toManyRelationshipKeys()
Overridden by subclasses to return the keys for the to-many relationship properties of the receiver. To-many relationship properties contain arrays of enterprise objects. EOClassDescription's implementation of this method returns null.
See Also: entityName, toOneRelationshipKeys, attributeKeys
public NSArray toOneRelationshipKeys()
Overridden by subclasses to return the keys for the to-one relationship properties of the receiver. To-one relationship properties are other enterprise objects. EOClassDescription's implementation of this method returns null.
See Also: entityName, toManyRelationshipKeys, attributeKeys
public String toString()
Returns a String representation of the receiver.
public String userPresentableDescriptionForObject(EOEnterpriseObject anObject)
Returns a short (no longer than 60 characters) description of anObject based on its data. This method enumerates anObject's attributeKeys and returns each attribute's value, separated by commas and with the default formatter applied for numbers and dates.
public void validateObjectForDelete(EOEnterpriseObject object) throws NSValidation.ValidationException
Overridden by subclasses to determine whether it's permissible to delete object. Subclasses should complete normally if the delete operation should proceed, or throw an exception containing a user-presentable (localized) error message if not. EOClassDescription's implementation of this method completes normally.
public void validateObjectForSave(EOEnterpriseObject object) throws NSValidation.ValidationException
Overridden by subclasses to determine whether the values being saved for object are acceptable. Subclasses should complete normally if the values are acceptable and the save operation should proceed, or throw exception containing a user-presentable (localized) error message if not. EOClassDescription's implementation of this method completes normally.
public Object validateValueForKey( Object value, String key) throws NSValidation.ValidationException
Overridden by subclasses to validate value. Subclasses should return null if the value is acceptable, or throw an exception containing a user-presentable (localized) error message if not. Implementations can replace value by returning a new value. EOClassDescription's implementation of this method returns null.
An enterprise object performs custom attribute specific validation with a method of the form validateKey. See the EOValidation interface specification for more information.
The following notifications are declared by EOClassDescription and posted by enterprise objects in your application.
public static final String ClassDescriptionNeededForClassNotification
One of the EOClassDescription-related methods in the EOEnterpriseObject interface to extend the behavior of enterprise objects is classDescription. The first time an enterprise object receives a classDescription message (for example, when changes to the object are being saved to the database), it posts ClassDescriptionNeededForClassNotification to notify observers that a class description is needed. The observer then locates the appropriate class description and registers it in the application. By default, EOModel objects are registered as observers for this notification and register EOClassDescriptions on demand.
| Notification Object | Enterprise object class |
| userInfo Dictionary | None |
public static final String ClassDescriptionNeededForEntityNameNotification
When classDescriptionForEntityName is invoked for a previously unregistered entity name, this notification is broadcast with the requested entity name as the object of the notification. By default, EOModel objects are registered as observers for this notification and register EOClassDescriptions on demand.
| Notification Object | Entity name (String) |
| userInfo Dictionary | None |
© 2001 Apple Computer, Inc. (Last Published April 19, 2001)