in v 4.0.7 i have ability create TStringField in designer and connct to both unicode database and 1 byte character database.
in 4.1.1 if i have created TstringField - i can connect only to 1 byte character database
if i have created TWideStringField - i can connect only to unicode database. Is it posible to allow make behaviour like in v 4.0.7?

What exactly do you mean by "i can connect only to 1 byte character database"? What exactly goes wrong?

if i have TStringField on form, then when i connect to unicode database
(AL32UTF8 - 4 byte char size) and open this form - i receive EDatabaseError with message "myDataSet: Type mistmach for field 'MyField', expected: String actual WideString"

If you do not want to make use of Unicode data, you can set Oracle.NoUnicodeSupport to True at run-time. At design-time you will still need to connect to a non-Unicode database though.

I have the same problem converting an old app. to Delphi 2010, but in my case I want the new version to be unicode compatible. What's the best way to proceed?

If my memory is correct, I searched all the units (*.pas and *.dfm) of my projects and replaced TStringField with TWideStringField, and ftString with ftWideString.

Hope this helps.

Roeland