Home: FDO Developer's Guide
Modifying Models
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Schema Management
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Rollback Mechanism
Schema Element States
All
elements within the model maintain a state flag. This flag can be
retrieved by calling FdoSchemaElement::GetElementState(), but it
cannot be directly set. Instead, its state changes in reaction to
the changes made to the model:
-
Unchanged. When
a schema model is retrieved via FdoIDescribeSchema, all elements
are initially marked Unchanged.
-
Detached. Removing
an element from an owning collection sets its state to Detached.
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Deleted. Calling
the Delete() method on an element sets its state to Deleted.
-
Added. Placing
an element within a collection marks the element as Added.
-
Modified. When
adding or removing a sub-element, such as a property element from
a class, the class element state will be changed to Modified.
Additionally, when
an element that is contained by another element is changed in any
way, the containing element is also marked as Modified. So, for
example, if a new value is added to the SchemaAttributeDictionary
of the “Class3” element in our model, both the “Class3” FdoClass
object and the FdoFeatureSchema object would be marked as Modified.
The state flags are
maintained until the changes are accepted, that is, when IApplySchema
is executed. At that time, all elements marked Deleted are released
and all other elements are set to Unchanged.
NoteWhen
you remove an element from an owning collection, its state is marked
as Detached. All collections currently in FDO are owning collections,
except for one, the collections FdoClassDefinition::GetIdentityProperties().