Combining Insert/Update to one Procedure

I can never understand why developers have both an Insert and an Update procedure, they do basically the same thing. If you combine them, you reduce the CRUD procedures by 25%, your DAL has 1 less method and management is simpler. By simply managing the ID field(s), you can combine these operations into 1 procedure.

ALTER PROC [APExclusionUpdate]
--Declare
  @ExclID INT,
  @EntityID INT,
  @AttrTypeID INT,
  @APLinkID INT,
  @Modified DATETIME,
  @ModifiedBy VARCHAR(100)
AS

-------------------- Created by Classbuilder -----------

IF ISNULL(@ExclID, 0) = 0 -- decide to Insert based on ID
  BEGIN
    INSERT  INTO APExclusion
            (EntityID,
             AttrTypeID,
             APLinkID,
             Modified,
             ModifiedBy
            )
    VALUES
            (@EntityID,
             @AttrTypeID,
             @APLinkID,
             @Modified,
             @ModifiedBy
            )
    SELECT
      SCOPE_IDENTITY() AS ExclID -- return the new ID value
  END
ELSE 
  BEGIN
    UPDATE
      APExclusion
    SET
      EntityID = @EntityID,
      AttrTypeID = @AttrTypeID,
      APLinkID = @APLinkID,
      Modified = @Modified,
      ModifiedBy = @ModifiedBy
    WHERE
      ExclID = @ExclID
    SELECT
      @ExclID AS ExclID -- return the passed in ID value
  END

This procedure decides whether to insert or update the record based on the ID fields. You can either return the ID or the new/updated record. I generally return the ID. I have used this with both identity and GUID primary keys, GUID requires a bit more management.