基于条件的Linq到SQL OrderBy和ThenBy

Question

I have to Query through a list then order it by the selections made by user.

User can have 3 levels of ordering. (ie: SortByItem1 , SortByItem2 , SortByItem3 )

This is what i currently have.

// searchResult is IQueryable
if (SortByItem1 == null && SortByItem2 == null && SortByItem3 == null)
{
    searchResult = searchResult.OrderBy(i => new { i.Name, i.Address }).ThenByDescending(i => i.CreatedDate); 
}
else {
    if(SortByItem1!=null)
    {
        if(SortByItem1=="Name") searchResult=searchResult.OrderBy(i=> i.Name);
        else if(SortByItem1=="Date") searchResult=searchResult.OrderBy(i=> i.CreatedDate);
        else if(SortByItem1=="Address") searchResult=searchResult.OrderBy(i=> i.Address);
    }
    if(SortByItem2!=null)
    {
        if(SortByItem2=="Name") searchResult=searchResult.OrderBy(i=> i.Name);
        else if(SortByItem2=="Date") searchResult=searchResult.OrderBy(i=> i.CreatedDate);
        else if(SortByItem2=="Address") searchResult=searchResult.OrderBy(i=> i.Address);
    }
    if(SortByItem3!=null)
    {
        if(SortByItem3=="Name") searchResult=searchResult.OrderBy(i=> i.Name);
        else if(SortByItem3=="Date") searchResult=searchResult.OrderBy(i=> i.CreatedDate);
        else if(SortByItem3=="Address") searchResult=searchResult.OrderBy(i=> i.Address);
    }
}

As you see this is not a reliable way of ordering. I want to have ThenBy ordering on every other trailing ordering. But simply using ThenBy instead of OrderBy is not allowed by Compiler.

How do I use multiple ordering for the records here?

Answer 1

Here is an idea. Instead of calling OrderBy all the time you could just define the ordering expressions, and call OrderBy and ThenBy all at once:

Expression<Func<SearchResultType, string>> first;
Expression<Func<SearchResultType, string>> second;
Expression<Func<SearchResultType, string>> third;

// determine which is which, assignment happens like this:
// first = i => i.Name;

searchResult = searchResult.OrderBy(first).ThenBy(second).ThenBy(third);

Answer 2

An improvement on @Andrei's answer would be to wrap this up in an extension method that you could call directly on any IQueryable<T> (it's easy enough to tweak this for IEnumerable<T> support)

public static IQueryable<T> SortBy<T>(this IQueryable<T> src, params Expression<Func<T, object>>[] filters)
{
    if (filters == null)
        return src;

    var result = src.OrderBy(filters.FirstOrDefault());
    foreach (var f in filters.Skip(1))
    {
        result = result.ThenBy(f);
    }
    return result;
}

This would allow for arbitrary sorting eg

// sort by name then by address and finally by date
var sorted = items.SortBy(x => x.Name, x => x.Address, x => x.Date);
// sort by date then by address
var sorted = items.SortBy(x => x.Date, x => x.Address);
// sort by name only
var sorted = items.SortBy(x => x.Name);

Live demo