Common Methods to Override

FormDataSource.Init

This method initializes the data source and is called from the super() of
FormRun.Init(). The method is only called once when the form opens.
The main task for this method is to initialize the query used for fetching data.
To modify or replace the query automatically created by the form, do this after
the super() call of this method.

FormDataSource.InitValue

This method is used to initialize a new record with default values. The super() of
this method calls the initValue() method on the underlying table.
If you have initialization that applies system-wide, put the code on the table.

FormDataSource.Active

This event is called when a new record becomes active in the data source. This
method is typically overridden to change properties which depend on the
contents of the current record: Commonly this method will:

• Modify permissions to the data source

• Modify permissions to the fields

• Enable/Disable buttons

FormDataSource.LinkActive

This method is the engine that joins data sources. This method is called on the
joined data source every time that the active record in the main data source is
changed. The method is also called when the form is opened as the system tries
to join the calling data source to the main data source of the called form. 

FormDataSource.ValidateWrite

This method validates an insert or update of a record.The super() of this method
calls the corresponding method on the underlying table.
If you need to distinguish between an insert and update, make a condition on theRecId field, which only has a value if it is an update.

FormDataSource.Write

This method controls the insert and update of records. The super() of this method
calls the corresponding method on the underlying table.
If you have form-specific tasks to perform in relation to the commitment of the
record, add it here.

Best Regards,
Hossein Karimi