Question

i want to replace operator(==, >= ,>…) in the clause where of linq lambda with parameter passed in method

the method:

public IEnumerable<Localisation> GetByFiltre(string filter, string valeurDate1)

/*
filter has the value of an operator:
>
==
!=
>=
<=
*/

    DateTime dt = Convert.ToDateTime(valeurDate1);

    var mod = from o in new GpsContext().Locals.Where(loc => loc.Date == dt)

i want to replace == in the clause where with the parameter filter
to obtain something like this

     var mod = from o in new GpsContext().Locals.Where(loc => loc.Date filter dt)

any body knows how to make it work ?

Answer 1

I think it’s better to make dictionary out of string filters and corresponding delegates.

class YourClass
{
     static readonly Dictionary<string, Func<DateTime, DateTime, bool>> s_filters = new Dictionary<string, Func<DateTime, DateTime, bool>>
     {
       {  ">", new Func<DateTime, DateTime, bool>((d1, d2) => d1  > d2) }
       { "==", new Func<DateTime, DateTime, bool>((d1, d2) => d1 == d2) }
       { "!=", new Func<DateTime, DateTime, bool>((d1, d2) => d1 != d2) }
       { ">=", new Func<DateTime, DateTime, bool>((d1, d2) => d1 >= d2) }
       { "<=", new Func<DateTime, DateTime, bool>((d1, d2) => d1 <= d2) }
     };

     public IEnumerable<Localisation> GetByFiltre(string filter, string valeurDate1)
     {
        ...

        DateTime dt = Convert.ToDateTime(valeurDate1);
        var filterDelegate = s_filters[filter];

        var mod = from o in new GpsContext().Locals.Where(loc => filterDelegate(loc.Date,dt));

        ...
     }
}