Question

Hi I have to apply filter on generic class. The sample class is as follows

public class Sample<T>
{
    List<T> sourceList = new List<T>();

    public void applyFilter(string propertyName , EnumOperator operator , object value)
    {

    }
}

Here I want to implement filter using linq or dynamic linq but am not getting any positive direction to implement this functionality.

Please give me some positive direction so that I can implement this functionality.

Thanks.

Answer 1

I would recommend returning an filtered list instead of modifying the source, and also the string “operator” is a C# keyword, so the signature of the method could be:

public List<T> ApplyFilter(string propertyName, EnumOperator operatorType, object value)
{
   ....
}

where I assume that the EnumOperator is an enum with values like this:

public enum EnumOperator
{
   Equal,
   NotEqual,
   Bigger,
   Smaller
}

and that you have some way to check if for an operator a value passes or fails the test, something along the lines of:

public static class OperatorEvaluator
{ 
  public static bool Evaluate(EnumOperator operatorType, object first, object second)
  {
    ...
  }
}

Given that, you can do something like:

public List<T> ApplyFilter(string propertyName , EnumOperator operatorType, object value)
{
  PropertyInfo pi = typeof(T).GetProperty(propertyName);
  List<T> result = sourceList.Where(item => { 
    var propValue = pi.GetValue(item, null);
    return OperatorEvaluator.Evaluate(operatorType, propValue, value);
  }).ToList();
  return result;
}

---

That said, you can always use LINQ’s methods to filter almost anything without resorting to reflection.