UFN_DATAFORMINSTANCE_EXTENSIONISVALID

create function dbo.UFN_DATAFORMINSTANCE_EXTENSIONISVALID
(
    @PARENTDATAFORMINSTANCEID uniqueidentifier,
    @EXTENSIONDATAFORMINSTANCEID uniqueidentifier
) 
    returns bit 
    with execute as caller
as
begin

    declare @PARENTRECORDTYPEID uniqueidentifier
    declare @EXTENSIONRECORDTYPEID uniqueidentifier
    declare @PARENTCONTEXTRECORDTYPEID uniqueidentifier
    declare @EXTENSIONCONTEXTRECORDTYPEID uniqueidentifier
    declare @PARENTMODE smallint
    declare @EXTENSIONMODE smallint
    declare @type1 uniqueidentifier
    declare @type2 uniqueidentifier

    -- a form cannot extend itself

    if @PARENTDATAFORMINSTANCEID = @EXTENSIONDATAFORMINSTANCEID
        return 0

    -- grab the mode and recordtypes associated with the forms

    select @PARENTRECORDTYPEID = DFT.RECORDTYPEID, @PARENTCONTEXTRECORDTYPEID = DFT.CONTEXTRECORDTYPEID, @PARENTMODE = DFT.MODE
        from dbo.DATAFORMINSTANCECATALOG DFI inner join dbo.DATAFORMTEMPLATECATALOG DFT on DFI.DATAFORMTEMPLATECATALOGID = DFT.ID
        where DFI.ID = @PARENTDATAFORMINSTANCEID
    select @EXTENSIONRECORDTYPEID = DFT.RECORDTYPEID, @EXTENSIONCONTEXTRECORDTYPEID = DFT.CONTEXTRECORDTYPEID, @EXTENSIONMODE = DFT.MODE
        from dbo.DATAFORMINSTANCECATALOG DFI inner join dbo.DATAFORMTEMPLATECATALOG DFT on DFI.DATAFORMTEMPLATECATALOGID = DFT.ID
        where DFI.ID = @EXTENSIONDATAFORMINSTANCEID

    -- if the mode differs, then the extension is invalid

    if @PARENTMODE <> @EXTENSIONMODE
        return 0

    if @PARENTMODE = 2
        begin
            -- for add forms, check the parent record type against the extension context record type

            set @type1 = @PARENTRECORDTYPEID
            set @type2 = @EXTENSIONCONTEXTRECORDTYPEID
        end
    else
        begin
            -- for edit and view forms, just compare the record types

            set @type1 = @PARENTRECORDTYPEID
            set @type2 = @EXTENSIONRECORDTYPEID
        end

    -- if the record types match, then the extension is valid

    if @type1 = @type2
        return 1

    -- if the record types are compatible, then the extension is valid

    if exists(select ID 
              from dbo.RECORDTYPECOMPATIBILITYMAP 
              where (RECORDTYPE1ID = @type1) and (RECORDTYPE2ID = @type2))
        return 1
    else 
        if exists(select ID 
              from dbo.RECORDTYPECOMPATIBILITYMAP 
              where (RECORDTYPE1ID = @type2) and (RECORDTYPE2ID = @type1))
        return 1

    -- the extension is not valid

    return 0;

end