Question

I have the following table:

if object_id(N'dbo.Node') is null
create table dbo.Node
(
    ID bigint identity primary key,
    ParentID bigint null, -- references Node(ID)
    DateCreated datetime not null,
    LastUpdated datetime not null,
    [Name] nvarchar(500) not null,
);

I have this trigger to achieve cascading deletes within the same table:

create trigger Node_Delete on Node for delete
as
begin
    delete from Node where ParentID in (select id from deleted)
end

Here’s my data set:

ID                   ParentID             DateCreated             LastUpdated             Name
534                  514                  2010-01-12 10:15:03.940 2010-01-12 10:15:03.940 Test 1
535                  534                  2010-01-12 10:15:08.563 2010-01-12 10:15:08.563 Test 2
536                  535                  2010-01-12 10:15:12.063 2010-01-12 10:15:12.063 Test 3
537                  536                  2010-01-12 10:15:18.510 2010-01-12 10:15:18.510 Test 4

Now I perform this query:

delete from Node where ID=534

And this is the resultant data set:

ID                   ParentID             DateCreated             LastUpdated             Name
536                  535                  2010-01-12 10:15:12.063 2010-01-12 10:15:12.063 Test 3
537                  536                  2010-01-12 10:15:18.510 2010-01-12 10:15:18.510 Test 4

Why does the DELETE statement in the trigger not cause a recursive execution of the trigger until all descended records are deleted?

EDIT: Note that I have posted a working solution below, but marked a different answer as correct, seeing as my question was not “what is the solution”, but rather “why does the way I’m doing it not work”.

Answer 1

You have to enable recursive triggers for the database. Notice that you can get only 32 levels deeper.

ALTER DATABASE databasename
SET RECURSIVE_TRIGGERS ON | OFF