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/*
Wotonomy: OpenStep design patterns for pure Java applications.
Copyright (C) 2000 Michael Powers
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, see http://www.gnu.org
*/
package net.wotonomy.control;
import net.wotonomy.foundation.NSArray;
/**
* EODataSource is used by EODisplayGroup.fetch() to retrieve a list of objects
* to display. When a display group has a data source, the display group will
* use the data source to populate the object list and to create new objects to
* be displayed in the list, and will update the data source when objects are
* inserted or removed from the list. <br>
* <br>
*
* In certain cases, as when a display group needs to populate a child display
* group to show a one-to-many relationship, the display group will call
* dataSourceQualifiedByKey to return a new data source that can vend objects
* associated with the specified key and then call qualifyWithRelationshipKey to
* specify the object and key that are the source of the child relationship.
* <br>
* <br>
*
* Concrete subclasses are expected to override fetch() and are required to
* override insertObject and removeObject.
*
* @author michael@mpowers.net
* @author $Author: cgruber $
* @version $Revision: 894 $
*/
public abstract class EODataSource {
/**
* Creates a new object. You should call insertObject() to insert the new object
* into this data source. This implementation attempts to create a new instance
* of the class returned by classDescriptionForObjects(). Override to return an
* object specific to your implementation.
*
* @return The newly created object, or null if new objects are not supported by
* this data source.
* @see #classDescriptionForObjects
*/
public Object createObject() {
Object result = null;
EOClassDescription c = classDescriptionForObjects();
if (c != null) {
result = c.createInstanceWithEditingContext(editingContext(), null);
}
return result;
}
/**
* Inserts the specified object into this data source.
*/
public abstract void insertObject(Object anObject);
/**
* Deletes the specified object from this data source.
*/
public abstract void deleteObject(Object anObject);
/**
* Returns the editing context for this data source, or null if no editing
* context is used. This implementation returns null.
*/
public EOEditingContext editingContext() {
return null;
}
/**
* Returns a List containing the objects in this data source. This
* implementation returns null.
*/
public NSArray fetchObjects() {
return null;
}
/**
* Returns a data source that is capable of manipulating objects of the type
* returned by applying the specified key to objects vended by this data source.
*
* @see #qualifyWithRelationshipKey
*/
public abstract EODataSource dataSourceQualifiedByKey(String aKey);
/**
* Restricts this data source to vend those objects that are associated with the
* specified key on the specified object.
*/
public abstract void qualifyWithRelationshipKey(String aKey, Object anObject);
/**
* Returns the description of the class of the objects that is vended by this
* data source, or null if this cannot be determined. This implementation
* returns null.
*/
public EOClassDescription classDescriptionForObjects() {
return null;
}
}
/*
* $Log$ Revision 1.2 2006/02/16 16:47:14 cgruber Move some classes in to
* "internal" packages and re-work imports, etc.
*
* Also use UnsupportedOperationExceptions where appropriate, instead of
* WotonomyExceptions.
*
* Revision 1.1 2006/02/16 13:19:57 cgruber Check in all sources in
* eclipse-friendly maven-enabled packages.
*
* Revision 1.5 2001/05/21 14:02:44 mpowers Corrected javadoc.
*
* Revision 1.4 2001/04/27 23:37:20 mpowers Now using EOClassDescription in the
* EODataSource class, as we should.
*
* Revision 1.3 2001/02/27 23:11:07 mpowers Removed object registration from
* createObject().
*
* Revision 1.2 2001/02/16 18:34:19 mpowers Implementing nested contexts.
*
* Revision 1.1.1.1 2000/12/21 15:46:38 mpowers Contributing wotonomy.
*
* Revision 1.3 2000/12/20 16:25:34 michael Added log to all files.
*
*
*/
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