[AccessD] Dlookup - where parameter being a form control vs a function

[Borge Hansen]

Hello everyone,
Anyone got an answer to this question?

So I've been replacing
[forms]![frmSystem]![txtUserName]
with a function
fGetApplicationParameter("CurrentLoggedInUser")
that returns the same text string
i.e. the UserName of the current logged in User in a User Profile
table called tblSystem

Below is the code for testing and comparing Dlookup with the similar
SQL select statement.
Notice that when we use the function on the DLookup it has to be
resolved outside of the third parameter of the DLookup whereas the
forms!frmSystem!txtUserName can be resolved as part of the third
DLookup parameter.

And using a plain SQL Select statement the Forms!frmSystem!txtUserName
is interchangeable with the function.

Why  the difference on the DLookup whereas the two SQL select
statements are similar in form?

/borge

=== code ===
?DLookup("NextAvailableUFN", "tblSystem", "UserName =
forms!frmSystem!txtUserName")
 900005
or
SELECT tblSystem.NextAvailableUFN, tblSystem.UserName
FROM tblSystem
WHERE (((tblSystem.UserName)=[forms]![frmSystem]![txtUserName]));

=> notice the difference here: UserName = ' " & etc & " '
?DLookup("NextAvailableUFN", "tblSystem", "UserName = '" &
fGetApplicationParameter("CurrentLoggedInUser") & "'")
 900005
or
=> notice: similar to =[forms]![frmSystem]![txtUserName])); above
SELECT tblSystem.NextAvailableUFN, tblSystem.UserName
FROM tblSystem
WHERE (((tblSystem.UserName)=fGetApplicationParameter("CurrentLoggedInUser")));