Why does sorting a GridView by more than one column only apply the order to the last term?

I've spent a good portion of my day fighting with GridView.Sort().

Nothing I did seemed to make it behave the way I would have expected. It wasn't until a coworker told me that within the expression you can specify the sort order for ea开发者_开发技巧ch term (except for the last one, apparently).

What is the purpose of supplying a sort direction if it's only applied to the last term in an expression containing multiple terms? For example:

GridView.Sort("Foo,Bar", SortDirection.Descending);

The term "Foo" in that expression will always be sorted in ascending order, while the term "Bar" has its sort order dictated by the SortDirection parameter of Sort(). However:

GridView.Sort("Foo DESC,Bar" SortDirection.Ascending);

The term "Foo" will now be sorted in descending order, and "Bar" in ascending order. I stumbled across this behaviour after the tip from my coworker when I tried this:

GridView.Sort("Foo DESC, Bar DESC", SortDirection.Descending);

An exception was thrown complaining that the column "Bar DESC" could not be found; this led me to believe that such expressions were not actually permissible. However, I was curious as to why no exception was thrown for "Foo DESC" (since it was listed first), so I tried this:

GridView.Sort("Foo DESC, Bar", SortDirection.Descending);

And finally saw the desired behaviour.

It appears as though I'm going to have to build the expression string manually since the sort order I need will vary on user input for the term "Foo", but remain consistent for the term "Bar". In all the searching I did I found no reference to this behaviour. Now that I understand how it works it makes sense that the first term is always ascending unless specified otherwise. But why not do away with the second parameter in Sort() and just leave the order (asc/desc) to the expression?

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Basically if the sort direction is descending, it adds DESC to the end, since ascending will never do this, you can just build your sort expression, set it to ascending and it'll effectively use only your first argument, like this:

GridView.Sort("Foo DESC, Bar DESC", SortDirection.Ascending);

I guess the majority of GridView sort cases are on a single column (and toggle asc/desc), that'd be the only reason I can think of for why the .Net team left the sorting this way.

I agree a .Sort(string sortExpression) should be there as well.

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Depending on your source, you could add a computed column of the fields to sort combined. For example: add a computed column SortOrder which is Foo + Bar (Assuming character strings). Then perform your sorts off of this for the desired column.

GridView.Sort("SortOrder", SortDirection.Ascending);

This solution works for those who don't want to add a GridView.Sorting event handler for the column or columns that contain multiple fields.

For those who don't want the additional column, you could adapt from this solution here.

protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
    {
        if (e.SortExpression == "Foo ASC, Bar ASC")
            e.SortExpression = "Foo DESC, Bar DESC";
        else if (e.SortExpression == "Foo DESC, Bar DESC")
            e.SortExpression = "Foo ASC, Bar ASC";
    }