Trigger that updates a column on the row where I clicked update - sql-server

Question

So I have this table:
ID Name IsDeleted
1 test True
2 test2 False
I currently have the following trigger:
CREATE TRIGGER [dbo].[Trigger_test_IsDeleted]
ON [dbo].[test]
INSTEAD OF DELETE
AS
BEGIN
SET NOCOUNT ON;
UPDATE dbo.test
SET IsDeleted = 1
WHERE ID = 1;
END
When I click the delete button on a row in my index view, I need this trigger to launch and set IsDeleted to 1 (or True) on that exact row. However, doing it with the above trigger will obviously delete only the row source where ID = 1. And if I leave out the WHERE statement, it sets IsDeleted for all rows to true.
I need my trigger to dynamically determine where "delete" is being pressed and only delete that row.
I know that in MySQL, you can accomplish this by using the following in a delete trigger:
SET new.IsDeleted = 1
Is there a way to get the same effect as "new." in SQL Server triggers?
And since we're on the topic, I want to achieve the same thing, but with altering the current code in the controller. Here is what it looks like now:
//POST - Delete
[HttpPost, ActionName("Delete")]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Delete(int? id)
{
var test = await _db.Test.FindAsync(id);
if (test== null)
{
return View();
}
_db.Test.Remove(test);
await _db.SaveChangesAsync();
return RedirectToAction(nameof(Index));
}
This code will achieve an ordinary delete operation on the database. I want to alter it to set "IsDeleted" to 1 instead of deleting the record.

Answer 1

If you want to update a flag instead of delete (which some people call it SOFT DELETE), you should update your trigger like this:
CREATE TRIGGER [dbo].[Trigger_test_IsDeleted]
ON [dbo].[test]
INSTEAD OF DELETE
AS
BEGIN
SET NOCOUNT ON;
UPDATE dbo.test
SET deleted.IsDeleted = 1
WHERE ID = deleted.ID; --<-- This is the key point
END

Answer 2

You need to examine the 'deleted' virtual table, and perform the update accordingly. EG:
create table test(id int primary key, IsDeleted bit default 0)
go
CREATE OR ALTER TRIGGER [dbo].[Trigger_test_IsDeleted]
ON [dbo].[test]
INSTEAD OF DELETE
AS
BEGIN
SET NOCOUNT ON;
UPDATE dbo.test
SET IsDeleted = 1
WHERE ID in (select id from deleted);
END
go
insert into test(id, IsDeleted) values (1,0),(2,0),(3,0)
delete from test where id = 2
select * from test
outputs
id IsDeleted
----------- ---------
1 0
2 1
3 0
(3 rows affected)