Cached updates

Working with cached updates

TMemTableEh can work in operative or postpone updates.

CachedUpdates property defines type if updates. In operative mode of the updates, TMemTableEh sends changed record to c right after application call TMemTableEh.Post method or append new record in TMemTableEh.

In the postpone mode the updates aren’t sent to postpone, but are accumulated in the special buffer. Data are not transferred until the client application calls the ApplyUpdates method.

To turn on the postpone updates you need set CachedUpdates property to True.

ApplyUpdates have a single parameter – MaxErrors. MaxErrors indicates the maximum number of errors that the DataDriver should allow before prematurely stopping update operations. Set MaxErrors to –1 to indicate that there is no limit to the number of errors. Set MaxErrors to 0 to define that whole process of change will be rejected on first error. Records, which renovations have come with errors, have an additional UpdateError property with type of TUpdateErrorEh.

To identify type of changing of record you need to use UpdateStatus method and StatusFilter property:

UpdateStatus indicates a type of changing of current record in MemTable. It returns one of the following values:

usUnmodified - Indicates that the current record haven’t been changed.

usModified - Indicates that the record was edited and changed.

usInserted - Indicates that the record was added.

usDeleted - Indicates that the record was removed.

StatusFilter defines filter for different types of records. StatusFilter – is a set that can contains any combination of the following values:

usUnmodified – Unmodified records are visible in MemTable.

usModified - Modified records are visible in MemTable.

usInserted - Added records are visible in MemTable.

usDeleted – Deleted record are visible in MemTable.

By default, StatusFilter have [usModified, usInserted, usUnmodified] value. So, deleted records are hidden.

Method RevertRecord restores an old condition of the current record and values of fields. If record was added in the program, it is deleted from the list. If record was changed then UpdateStatus property is restored to usUnmodified value.
Method MergeChangeLog deletes a log of cached changes. All added or changed records get usUnmodified status.

Method CancelUpdates cancels all changes and restores old state of records array.