DataView.Sort - more than just asc/desc (need custom sort)

Question

I've got a report being built from a dataset. The dataset uses the Sort property to order the data. I know that I can create a sort expression like this:

"field desc, field2 asc"

But what I need now is a way to do a custom sort. In SQL, I can perform a custom sort by doing something like this:

order by 
    case when field = 'Some Value' then 0 end
    case when field = 'Another Value' then 1 end

To basically re-define my sort (i.e, Some Value comes before Another Value).

Is it possible to do something similar as a sort expression against a DataView?

Answer 1

I don't think so. You could however change you SQL to return a "CustomSort" column that is the result of your case statement:

select
    (case when f = 'a' then 0 else 1 end) as CustomSort
from MyTable

Answer 2

You could use an if or a switch statement to get similar functionality to the select case statement:

            if (Something == "1")
                MyView.Sort = "Field1 ASC";
            else
                MyView.Sort = "Field2 ASC";

OR

            switch (MyProperty)
            {
                case 1:
                    MyView.Sort = "Field1 ASC";
                    break;
                case 2:
                    MyView.Sort = "Field2 ASC";
                    break;
                default:
                    MyView.Sort = "Field3 ASC";
                    break;
            }

Answer 3

Ok, I just whipped this up real quick, and didn't do all the neccessary error handling and null checking, but it should give you an idea and should be enough to get you started:

public static class DataTableExtensions
{
    public static DataView ApplySort(this DataTable table, Comparison<DataRow> comparison)
    {

        DataTable clone = table.Clone();
        List<DataRow> rows = new List<DataRow>();
        foreach (DataRow row in table.Rows)
        {
            rows.Add(row);    
        }

        rows.Sort(comparison);

        foreach (DataRow row in rows)
        {
            clone.Rows.Add(row.ItemArray);
        }

        return clone.DefaultView;
    }


}

Usage:

    DataTable table = new DataTable();
    table.Columns.Add("IntValue", typeof(int));
    table.Columns.Add("StringValue");

    table.Rows.Add(11, "Eleven");
    table.Rows.Add(14, "Fourteen");
    table.Rows.Add(10, "Ten");
    table.Rows.Add(12, "Twelve");
    table.Rows.Add(13, "Thirteen");

//Sort by StringValue:

 DataView sorted = table.ApplySort((r, r2) =>
        {
            return ((string)r["StringValue"]).CompareTo(((string)r2["StringValue"]));
        });

Result:

11 Eleven

14 Fourteen

10 Ten

13 Thirteen

12 Twelve

//Sort by IntValue:

DataView sorted = table.ApplySort((r, r2) =>
            {
                return ((int)r["IntValue"]).CompareTo(((int)r2["IntValue"]));
            });

Result:

10 Ten

11 Eleven

13 Thirteen

12 Twelve

14 Fourteen

EDIT: Changed it to extension method.

Now in your Lambda, (or you can create a full blown Comparison method) you can do any kind of custom sorting logic that you need. Remember, -1 is less than, 0 is equal to, and 1 is greater than.

Answer 4

I like BFree's answer, though I'd worry about the risk that my code would end up updating the cloned table rather than the real one. (I haven't thought through it enough to know if that's actually an issue if you're only using the extension method in a DataView.)

You can do this on the original DataTable by adding a calculated DataColumn to it (using the Expression property) and then sorting on its value.

In your case it would be something like:

DataColumn c = myTable.Columns.Add("Sort", typeof(int));
c.Expression = "iif(field='SomeValue', 0, iif(field='AnotherValue', 1, 2))";

which sorts SomeValue first, AnotherValue second, and everything else after that.