Question

I have an 3-layered project, so that all Linq-Querys himself are in the DAL.
Now I have a filter function implemented in the Desig-Layer and want easily filter there, but how?

            Business.UserHandling uh = new Business.UserHandling();
            List<DAL.Benutzer> users = uh.GetUserOverview();
            gridUserOverview.AutoGenerateColumns = false;
            gridUserOverview.DataSource = users;
            gridUserOverview.DataBind();

How can I user something like “users = users.Where(“bla = 1″)”?

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I tried:

                Business.UserHandling uh = new Business.UserHandling();
            List<DAL.Benutzer> users = uh.GetUserOverview();

            var filters = new Dictionary<string, object>();
            filters.Add(Request.QueryString["value"], Request.QueryString["text"]);
            users = users.Where(user => filters.All(filter => user.GetType().GetProperty(filter.Key).GetValue(user, null) == filter.Value)).ToList();

            gridUserOverview.AutoGenerateColumns = false;
            gridUserOverview.DataSource = users;
            gridUserOverview.DataBind();

But it fails… I filtered on “UserID = 1”, I have 2 Users, the filter should be filter 1 of these 2. But the return is 0 users.

Answer 1

In order to use a dynamic filter you can build a dictionary and verify the filter by reflection:

var filters = new Dictionary<string, object>();
filters.Add("bla", 1);
users.Where(user => filters.All(filter => user.GetType().GetProperty(filter.Key).GetValue(user, null) == filter.Value));

Edit Support all types convertible from string:

var users = new List<User>();
users.Add(new User {Age = 1 });
users.Add(new User { Age = 2 });
var filters = new Dictionary<string, string>();
filters.Add("Age", "1");
var filtered = users.Where(user => filters.All(filter =>
       {
           var propertyInfo = user.GetType().GetProperty(filter.Key);
           return Equals(propertyInfo.GetValue(user, null) , Convert.ChangeType(filter.Value, propertyInfo.PropertyType));
       }));

Assert.AreEqual(1, filtered.Count());