Question

On my view there is a datatable holding a collection of ServerRow and 4 textboxes (Hostname, OS, Location, Zone). When the user types into any of the 4 boxes I want to immediately filter this list. I have this code setup and ready to go that on the set method of each textbox property I call the filter method.

Now onto the problem: if I have 4 criteria that means I have 2 to the power of 4 different scenarios. What I would like to do is write a linq statement with all of these scenarios dealt with such that if any of the properties are NullOrEmpty they will not be used in the Where clause and on the flip side if there is a value the corresponding field will be searched with a Contains.

Example

AvailableCis = New ObservableCollection(Of ServerRow)
                (_CiData.Where(Function(ci) ci.OS.ToUpper
                .Equals(_selectedOS.ToUpper) AndAlso 
                ci.HostName.ToUpper.Contains(_ciNameFilterText.ToUpper))
                .OrderBy(Function(a) a.CiName))

This example shows how it works with 2 criteria and both of those criteria are set.

Answer 1

You can use lazy evaluation to solve this problem –

String.IsNullOrEmpty(ci.OS) OrElse ci.OS.ToUpper.Equals(_selectedOS.ToUpper)

This way if the string is null or empty the second clause is not evaluated and all ServerRows are accepted.

Also don’t forget that AndAlso has a higher precedence than OrElse, so each clause has to be wrapped in brackets.