ODAC (V9.5.15) study notes (iv) Tmemdataset (1)

Source: Internet
Author: User

All dataset class components are inherited from Tmemdataset, which implements the management of data in memory, with its main properties, methods, and events as follows.

1. Data Update

Name

Type

Description

Cachedupdates

Boolean

Whether the data set uses buffered mode

Applyupdates

Commits uncommitted data in the buffer to the database, but does not perform transactional operations on the database. The buffer data still exists and the UpdateStatus state is modified, calling Commitupdates to clear the cached data and revert the state to a non-modified state. Applyupdates is not placed in the try exception block, if there is a data update failure, the exception information prompt will be triggered, and if updateaction is not set to Uaabort in Onupdateerror, the error message prompt will be triggered again.

Cancelupdates

Discard changes to uncommitted data in the buffer to restore the original state

Restoreupdates

Restores all buffer data in the dataset to the update state prior to the call to Applyupdates, with a version used when the update failed

Commitupdates

Clears uncommitted data from the buffer, but changes skipped through Onupdaterecord or Onupdateerror events are not cleared

Updatespending

Boolean

Determines whether the buffer has uncommitted data, true indicates that there is

UpdateStatus

Tupdatestatus

Returns the update status of the dataset under the current record.

Updateresult

Tupdateaction

Returns the execution state of the data set after the call to the Applyupdates method in that record

Updaterecordtypes

Returns the update mode of the current record in buffered mode

Localupdate

Boolean

Whether the update is local or True will prevent the dataset from automatically submitting the data to the server, but rather buffering it in local memory.

Deferredpost

Unlike post, Deferredpost permanently saves the modified commit database that has been completed, while the dataset state remains in edit or new (DsEdit, Dsinsert), and calling the Cancel function does not cancel the modified content of the committed database. Use on the need to be cautious

revertrecord

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in buffered mode, undo data updates to the current record

onupdaterecord

 

triggers when a record is updated, and if it is in buffered mode, the event is triggered after applyupdates. The updateaction default for the event is uafail, which needs to be set to uaapplied if the code operation succeeds. The values are as follows:

uafail    trigger failure exception information

uaabort        interrupts subsequent updates and rolls back

uaskip     Skip, but do not error

uaretry        Try again, it is easy to form a dead loop

uaapplied     code has been processed and ODAC is no longer automatically processed

Onupdateerror

Triggered when a data update has an error, and if it is in buffered mode, the event is triggered after applyupdates. The updateaction of the event defaults to Uafail, By accessing the event arguments DataSet's Fields Tfield.oldvalue and Tfield.newvalue get the original value and the new value, setting the updateaction of the event to Uaretry can retry the update. Applyupdates is not placed in the try exception block, the exception information prompt will be triggered, and if updateaction is not set to Uaabort in Onupdateerror, the error message prompt will be triggered again.

ODAC (V9.5.15) study notes (iv) Tmemdataset (1)

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