MS-Access unbound ComboBox in DataSheet?

In ms-access 2007, i'm trying to make a form for a table. this table has foreign keys from 2 parent tables. so i thought i would make these fields a lookup. but i couldn't create a single lookup for each parent table because they are composite keys.

I decided to create a query in which for each of these parent tables and the child table with an extra field for each composite key. this works fine with a normal form using an unbound ComboBox... but the unbound ComboBox does not work in a DataSheet Subform. when i make changes to a ComboBox in the Subform code, they are applied to all the other ComboBoxes in the same column as well.

My questions:

• is th开发者_Python百科ere a way to change the values of the individual unbound ComboBox?

• is there a different control i should be using other than the ComboBox or the DataSheet Subform?

• what is the normal work around for this situation?

I cannot bind the ComboBox's because the field from the query is calculated/an-expression as I said.

I ran across a form of this problem myself, so for the sake of posterity:

While generally, the advice "Don't use continuous forms/datasheets in this situtation" is the best advice...It is possible to work around this.

However, access will not let you update the value of a single control on a datasheet. What can be used instead in this case is a temporary table, which can, when used as a recordsource, become the values of those controls. You will need to repopulate the table, and requery the controls (requerying the entire form should work as well) every time the calculation needs to change, however. Furthermore, should you enable editing on the controls, you will have to write some VBA on each control to handle the update event (Before Update), and run your own query to update the source tables, not merely the temporary table. Annoying to do perhaps, but effective.

There is another possibillity, which may also work, but I haven't tried to do something quite like this myself. The rowsource of a combobox can be very complex, so it is probable that you do not need to update the comboboxes with VBA at all. The rowsource can depend on other controls (such as another combobox) using the syntax Me.Form!controlName or Forms!FormName!ControlName, which will allow you to form the composite key. Of course, you can also select from queries with a rowsource. What is more interesting is that queries can reference controls on your form, provided the form is open, and you should safely be able to modify that with VBA should you have to.

Between the two of these, you should be able to force access, kicking and screaming, to display any data you wish, even on a datasheet, and to allow the user to change that data (but only if you want it to), and using the BeforeUpdate event, drag modified data back to whatever table it came from.

Continuous forms and datasheets do not work well for editing in situations where combo boxes need to be changed conditionally. The problem is that if you use the OnCurrent event to set the Rowsource of the combo box, it will be OK for that row, but will then hide the stored values for other rows.

The solution is to never use continuous forms/datasheets for editing data when this is the case (I hardly ever use them for editing, in fact). You can create two subforms, a continuous/datasheet subform that functions as a list, and a detail subform, that displays one record. Make the list subform uneditable, and the detail subform editable. You can link the two of them by using the Link Child/Link Master property of the detail subform control, and set it to the PK of the list subform.

If your list subform is Me!List and your detail is Me!Form, and the PK field is MyID, your link properties for the detail subform would be:

  Master: Me!List.Form!MyID
  Child:  MyID

When you move to a different record in the list form, it will be automatically loaded in the child form. Any edits to the previously displayed detail will be saved before record departure.