SQL Server Default Column value from function - sql

Question

I want to set default value to Id column in Person table with a function
that goes like this:
Function:
IF OBJECT_ID ( 'GetLastId','FN') IS NOT NULL
DROP function GetLastId;
GO
CREATE FUNCTION [dbo].[GetLastId]
(#TableName nvarchar(max))
RETURNS int
AS
BEGIN
DECLARE #LastId int;
DECLARE #sql nvarchar(max);
SET #sql = 'SELECT #LastId = ISNULL(MAX(Id), 0) + 1 FROM ' + #TableName + ';'
EXECUTE sp_executesql #sql, N'#LastId int output', #LastId = #LastId output;
RETURN #LastId
END
and then:
UPDATE Person
SET Id = dbo.GetLastId('Person')
Running this code throws an error:
Only functions and some extended stored procedures can be executed from within a function.
So how to fix this and make it work as a default value?
And please do not say "Use triggers..." as I intend to use it with Entity Framework Core as default value for primary keys.
Thanks

Answer 1

You want a stored procedure, not a function:
create procedure [dbo].[GetLastId] (
#TableName nvarchar(max),
#LastId int output
) as
begin
declare #sql nvarchar(max);
set #sql = 'select #LastId = ISNULL(MAX(Id), 0) + 1 from ' + #TableName + ';'
EXECUTE sp_executesql #sql,
N'#LastId int output',
#LastId=#LastId output;
end;
You should also use quotename() around the table name to prevent unexpected things from happening.
Then you would call this as:
declare #lastId int;
exec dbo.GetLastId('Person', #lastid output);
update Person
set Id = #lastId;

Answer 2

You need to create stored procedure instead of function
create procedure [dbo].[GetLastId] (
#TableName nvarchar(max),
#ColumnName nvarchar(200),
#LastId int output
) as
begin
declare #sql nvarchar(max);
set #sql = 'select #LastId = ISNULL(MAX('+ #ColumnName +'), 0) + 1 from ' + #TableName + ';'
EXECUTE sp_executesql #sql,
N'#LastId int output',
#LastId=#LastId output;
end;
Then you can execute sp like below
declare #lastId int
exec dbo.GetLastId 'Person', 'Id' , #lastid output;
select #lastId
update Person
set Id = #lastId;