The DiscardChanges OCL operator lets you cancel pending changes for a collection of objects, making it useful when you want a user to abandon edits in a ViewModel.

What DiscardChanges does

DiscardChanges iterates over the objects in the collection that precedes it and reverts their pending state to the last known state in persistent storage (the database).

It discards changes that have not been saved, including pending edits, additions, and deletions for the objects in the collection. It does not save anything to persistent storage.

Use DiscardChanges for a Cancel action, or whenever you need to abandon the unsaved changes currently tracked by a ViewModel.

Syntax

collection->DiscardChanges

Part	Meaning
collection	The collection of objects whose pending changes you want to discard.
->DiscardChanges	Reverts the objects in that collection to their last known persistent state.

Discard all pending changes in a ViewModel

selfVM.DirtyList returns all changed objects that would be saved if selfVM.Save were called. To cancel all pending changes in the current ViewModel, use:

selfVM.DirtyList->DiscardChanges

For example, place this expression in the action that handles a Cancel button. When the action runs, the ViewModel's currently changed objects are reverted instead of being committed.

Choose discard or save

If you want to...	Use
Keep the pending changes by committing them to persistent storage	Save
Abandon pending changes for a collection of objects	collection->DiscardChanges
Check whether an object has changed since its last save	IsDirty

Important behavior

• Call DiscardChanges on the collection whose pending changes you intend to cancel. The collection determines which objects are reverted.
• Use selfVM.DirtyList->DiscardChanges when the intended scope is every changed object in the current ViewModel.
• Changes that have already been committed with Save are not pending ViewModel changes and are not undone by this operator.

See also

• Documentation:SelfVM.DirtyList
• Documentation:OCLOperators Save
• Documentation:OCLOperators IsDirty
• Documentation:OCL Boolean Operators