delete constraint

how can i implement delete constraint? i mean i don't want the rows of the primary key table to be deleted if they are used as foreign key in some other table. so i want to check if that PK is used as foreign key in other tables before deleting.INSTEAD OF DELETE triggers|||so u mean using triggers instead of delete cascade? i can check if that record exists in other tables using triggers and take necessary action but i want to return relevant message to user if it couldn't be deleted. how can i do that?|||Have a look at RAISERROR|||i was able to manage the following code but couldn't get the message displayed when user tries to delete the record. if i run the stored proc from query analyzer, i get the following error message but not in my application. i have tried catching any exceptions using ex.Message but can't get the error. so how can i get the error displayed when user violates the delete constraint? i have used ExecuteNonQuery command.

IF EXISTS (SELECT id FROM A WHERE ID = @.ID)
BEGIN
RAISERROR ('Cannot delete this record. Make sure that this record is not used in other tables',9,1)
RETURN
END

|||Try ON DELETE {NO ACTION and ON UPDATE {NO ACTION, this will not allow Deletes and Updates. Hope this helps.

Kind regards,
Gift Peddie|||but i want the message to be returned if it couldn't be deleted so that relevant message can be displayed to the user.|||CREATE TABLE order_part
(order_nmbr int,
part_nmbr int
FOREIGN KEY REFERENCES part_sample(part_nmbr)
ON DELETE NO ACTION,
qty_ordered int)
GO

CREATE TABLE order_part
(order_nmbr int,
part_nmbr int
FOREIGN KEY REFERENCES part_sample(part_nmbr)
ON UPDATE NO ACTION,
qty_ordered int)
GO

Run a search in the BOL(books online) for Cascade Delete, the following code is from the BOL it means deletes or updates will fail with an error message. Hope this helps.

Kind regards,
Gift Peddie|||but how can we be sure about the source of error this way? with raiserror as i have done, i can get the message if there are other errors as well. else i don't get any error message. isn't that suupposed to return error message?|||The error from NO ACTION is ANSI SQL from DRI(Declarative Referential Integrity) rules but if you prefer Raise Error you can use it run a search for raise error in the BOL(books online). Hope this helps.

Kind regards,
Gift Peddie|||

I do it this way, for now. Probably better way would be to make Delete function that returns an error message rather then raising new exception. Maybe even make a some kind of class that interprets these error numbers and returns standard error message.

In SqlDataProvider for module

PublicOverridesSub DeleteClientDepartmentsItem(ByVal itemIDAsInteger)

Try

SqlHelper.ExecuteNonQuery(_connectionString, _databaseOwner & _objectQualifier & _

"esr_ClientDepartments_Delete", itemID)

Catch exAs SqlException

If ex.Number = 547Then

ThrowNew Exception("This record cannot be deleted due to its association with other records.")

EndIf

EndTry

EndSub

'in the page:

Try

Dim cdcAsNew ClientDepartmentsController

Dim departmentIdAsInteger =CType(dgDepartments.DataKeys(e.Item.ItemIndex),Integer)

cdc.Delete(departmentId)

BinddgDepartments()

Catch exAs Exception

DotNetNuke.UI.Skins.Skin.AddModuleMessage(Me, ex.Message, Skins.Controls.ModuleMessage.ModuleMessageType.YellowWarning)

EndTry