How can I take a class and allow the methods to accept a generic list

Question

I would like to take the ResultSet class shown below and modify it so it can be generic. As you can see, it only accepts Product List but I would like it to take List-OneOfMyModels> or List-T> for the sake of code re-usability in my controllers.

public class ResultSet
{
    public List<Product> GetResult(string search, string sortOrder, int start, int length, List<Product> dtResult, List<string> columnFilters)
    {
        return FilterResult(search, dtResult, columnFilters).SortBy(sortOrder).Skip(start).Take(length).ToList();
    }

    public int Count(string search, List<Product> dtResult, List<string> columnFilters)
    {
        return FilterResult(search, dtResult, columnFilters).Count();
    }

    private IQueryable<Product> FilterResult(string search, List<Product> dtResult, List<string> columnFilters)
    {
        IQueryable<Product> results = dtResult.AsQueryable();

        results = results.Where(p => (search == null || (p.Name != null && p.Name.ToLower().Contains(search.ToLower()) || p.PublicDisplayNo != null && p.PublicDisplayNo.ToLower().Contains(search.ToLower())))
            );

        return results;
    }
}

And in my controller I call the method like so:

 public JsonResult DataHandler(DTParameters param)
    {
        try
        {
            var dtsource = _context.Products.ToList();

            List<String> columnSearch = new List<string>();

            foreach (var col in param.Columns)
            {
                columnSearch.Add(col.Search.Value);
            }

            List<Product> data = new ResultSet().GetResult(param.Search.Value, param.SortOrder, param.Start, param.Length, dtsource, columnSearch);
            int count = new ResultSet().Count(param.Search.Value, dtsource, columnSearch);
            DTResult<Product> result = new DTResult<Product>
            {
                draw = param.Draw,
                data = data,
                recordsFiltered = count,
                recordsTotal = count
            };
            return Json(result);
        }
        catch (Exception ex)
        {
            return Json(new { error = ex.Message });
        }
    }

Answer 1

This should get you going:

using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices.ComTypes;

public class ResultSet
{
    public List<T> GetResult<T>(string search, string sortOrder, int start, int length, List<T> dtResult, List<string> columnFilters) where T : class
    {
        return FilterResult(search, dtResult, columnFilters).OrderBy(sortOrder).Skip(start).Take(length).ToList();
    }
    public int Count<T>(string search, List<T> dtResult, List<string> columnFilters) where T : class
    {
            return FilterResult(search, dtResult, columnFilters).Count();
    }

    private IQueryable<T> FilterResult<T>(string search, List<T> dtResult, List<string> columnFilters) where T : class
    {
        IQueryable<T> results = dtResult.AsQueryable();

        results = results.Where(p => (search == null || (p.Name != null && p.Name.ToLower().Contains(search.ToLower()) || p.PublicDisplayNo != null && p.PublicDisplayNo.ToLower().Contains(search.ToLower()))));

        return results;
    }
}

This won't support the cases where you are using properties on the generic type, T, because I have only typed it as a class. You can change the typing following the documentation here . You'll want to type it with a base class or an interface to get things like p.Name to work.

Answer 2

You would have to make the whole generic like public class ResultSet<T> or make the methods in the class have generic input and return types like so public List<T> GetResult(params) .

But this introduces a new problem in the filter result method which uses the actual Products class to perform search and filter by its properties. Use Reflections in c#, System.Reflection to look-up class property values of generic types.