Populating a Combo Box from a Recordset

Combo boxes, list boxes, and other bound controls maintain a connection to their underlying Jet tables. Combo boxes create their connection when you open the combo list. List boxes create a connection when you open the form. Neither connection closes until you close the form. Connections to tables create permanent user read locks; updating a table creates a temporary write lock during the update process.

A Jet database has a maximum of 255 concurrent user locks. You seldom, if ever, run out of locks in a single-user environment, but it's quite easy to hit the Jet lock limit with a widely deployed multiuser application that uses combo and list boxes. For example, 50 simultaneous users of the decision-support application described in Chapter 29, "Programming Combo and List Boxes," would generate 200 read locks, because two combo boxes and two list boxes are on the form. As the application gains more users, Jet might run out of read locks. In such a case, some users encounter a runtime error when attempting to open a combo box.