Advantages of Manual vs. Automatic DataEnvironment Behavior

• Microsoft Visual FoxPro for Windows, version 3.0

SUMMARY

The tables in the DataEnvironment can be opened and closed manually or automatically. Both manual and automatic opening and closing have certain advantages.

MORE INFORMATION

If the DataEnvironment's AutoOpenTables and AutoCloseTables properties use their default setting of True (.T.), you don't need to write any code to take care of opening and closing the tables and views in the DataEnvironment.

Setting the DataEnvironment's AutoOpenTables property to False (.F.) gives the developer a bit more control. Tables are automatically opened before the form's Load event occurs but after the DataEnvironment's BeforeOpenTables event. This means that if code in the form's Load event determines an error condition (such as user opening a form that he or she does not have permission to use) and returns False (.F.) to keep the form from opening, a performance penalty results because the tables were opened but never used. In this case, manually calling the DataEnvironment's OpenTables method after checking the user's security clearance would speed up the application. Actually opening the tables with the OpenTables method is not significantly faster or slower than letting the DataEnvironment automatically open them, but time can be saved by not opening the tables at all if they are not be needed.

If many or all of the tables in a DataEnvironment are used by the next form, formset, or report's DataEnvironment, setting the DataEnvironment's AutoCloseTables property to False (.F.) speeds up the loading of the next DataEnvironment, because the tables are already open.