Access Cookbook, 2nd Edition [Electronic resources] نسخه متنی

Recipe 14.4 Fill the Drop-Down Lists When Using ServerFilterByForm in an ADP

14.4.1 Problem

You have turned on the
ServerFilterByForm property. However, when users open the form and
select from the combo boxes, the only choices are
Is Null and
Is Not Null.
How do you get the combo boxes to show a list of valid values for
that field?

14.4.2 Solution

If you turn on the ServerFilterByForm
property, your form will open in a special view that turns text boxes
into combo boxes. This allows users to define their own server
filters at runtime, which are then processed by SQL Server before the
record source data is returned to the form. However,
you'll often see only the values shown in Figure 14-8 when you expand one of the combo boxes.

Figure 14-8. Combo boxes with only Is Null and Is Not Null options

Each text box on the form has a
FilterLookup property that has three settings:

A combo box list will contain only two items: Is
Null and Is
Not Null.

A combo box with a full list of values will be created for that text
box.

Access will populate the list either with all the values or with only
Is Null/Is Not Null, depending on the settings in the Edit/Find tab
of the Tools Options dialog shown in Figure 14-9.

Figure 14-9. Database options that affect ServerFilterByForm

Follow these steps to change the database defaults to always show a
list of available items when using
ServerFilterByForm:

1. Open the database whose options you want to change.

2. Choose Tools Options from the menu.

3. Check the "Records at server"
   option shown in Figure 14-9.

If you don't want to change this option globally,
followthese steps to set the list of values on a form-by-form basis:

1. In design view, open the form in which you want to enable a full list
   of values for ServerFilterByForm. Select all the text boxes you want
   to enable.

2. Set the FilterLookup property on the Data tab in the properties sheet
   to Always, as shown in Figure 14-10.

Figure 14-10. Set the FilterLookup property for the control on a form

When you open the form to filter records now, you'll
see some real data in the combo boxes, as shown in Figure 14-11.

Figure 14-11. The combo boxes now display real data

14.4.3 Discussion

The data to populate the combo boxes
must, of course, come from the server. Setting the FilterLookup
property for the controls or setting the "Records at
server" option for the entire project runs
additional queries that populate each combo box with a domain of real
values from which the user can choose.

When you set the ServerFilter property on a form, regular filtering with the form's Filter property is unavailable.

Because populating combo boxes with real
values entails extra round trips to the server to retrieve the data
for the lists, it defeats the purpose of using the ServerFilter
property in the first place, so don't overuse this
feature. The benefit is that the interface is more user-friendly when
the user can select from actual values instead of guessing.

You'll have to evaluate your own applications to
determine whether or not the extra data filtering is worth the extra
load on the server. If the form would otherwise load a lot of
records, and if the lists you are loading aren't too
big, you would probably improve performance by using
ServerFilterByForm. To be safe, adjust the
ServerFilterByForm setting at the control level
rather than by setting the database default for the entire project.