如何使用不在列表中的值实现TDataSet绑定的组合框

Question

I need to implement a combobox, which is bound to a TpFIBDataSet (descendant of TDataSet ). I've done this several times before. It's not a big thing if it contains only predefined values.

This time, I'd like to have a combobox that accepts custom values entered by the user, also giving the ability to the user to select some predefined value. Newly entered values shall be inserted into some table of the database just before the record the combobox's field belongs to is posted.

The main problem seems to me, that predefined values are internally represented as integer IDs (the combobox I use is TwwDBComboBox from Roy Woll's InfoPower package, as it implements maplist functionality) because the field is a foreign key, while custom values may be nearly everything (only restricted by a mask).
How can I distinguish between an integer ID and integer user-input, for example?

See the set properties of the combobox:

AComboBox.Style   := csDropDown;
AComboBox.MapList := True;

I don't request a solution as take this piece of code and be happy . I'm rather looking for some advice by others who might have or had a similar problem.

Answer 1

How can I distinguish between an integer ID and integer user-input, for example?

You go back to the database. Either query directly select count(*) from table where id = ComboBoxId .
Or use the Locate method of the dataset.
Or keep a cache handy in a MyList: TList<Integer> and do a MyList.BinarySearch to see if the item is already in the DB.
Obviously the cache will only work if the DB is single-user, because otherwise you will not be able to keep it up-to-date.

If it is not in the DB, you run the insert query. After it's inserted you run the default combobox behavior, because now the values is sure to be in the DB.