ASPxComboBox supports custom data binding and filtering that allow you to populate the editor with data according to your custom scenario.
In this demo, the ASPxComboBox does not perform filter operations at the database level directly. Instead, the editor handles the ItemsRequestedByFilterCondition and ItemRequestedByValue events and uses LINQ expressions to target a data source and retrieve small portions of data.
When ASPxComboBox is in incremental filtering mode, it has the capability to start filtering only after an end-user has typed a specific number of symbols in the editor's text box. The FilterMinLength property can be used to define the minimum length of the filter string input. Once the minimum length is reached, filtering operations are initiated.
This behavior is extremely useful when ASPxComboBox works with a large amount of data. In this case, due to the large size of the data set, performing filtration on each typed symbol is inefficient and may affect application performance. Thus, by delaying the start of filter operations using this minimum length requirement, you can provide end-users with more accurate results and improve performance of your page.
Refer to the "Large Database (Server Mode)" demo to review how to generate SQL requests to a large database automatically using the LinqServerModeDataSource or EntityServerModeDataSource data sources.