Passing a field to a function to sort on that field

Question

I am writing a function with a signature like this where I am sorting the model data among other things:

public MyModel GetModel(IQueryable<Something> query, string sort, 
   int page, int PageSize)
{
   ...
   viewModel.Something = query.OrderByDescending(o => sort)
          .Skip((page - 1) * pageSize).Take(pageSize).ToList();
   ...
}

Problem is I want to pass in a default sort parameter which is what I want to sort against if the parameter "sort" is null or empty. For example, this might be:

.OrderByDescending(o => o.AddedDate);

I have tried all sorts of things (for instance passing in a Func) to pass in something to this function to tell it to use AddedDate or whatever I choose to sort the records if sort is null but nothing works. How would I implement such a thing?

possible duplicate of [Dynamic LINQ OrderBy](http://stackoverflow.com/questions/41244/dynamic-linq-orderby) — Eranga, Jan 25 '12 at 14:45

score 3 · Accepted Answer · answered Jan 25 '12 at 14:45

3

Your current code doesn't make much sense - you are sorting by a single value, not a property of the items you want to sort - if you want to be able to sort by any string property within your Something class more appropriate would be:

public MyModel GetModel(IQueryable<Something> query, Func<Something, string> sort, 
   int page, int PageSize)
{
   Func<Something, string> actualSort = sort ?? (o => o.AddedDate);
   ...
   viewModel.Something = query.OrderByDescending(actualSort)
          .Skip((page - 1) * pageSize).Take(pageSize).ToList();
   ...
}

Now if you pass in null for sort the sorting will revert to the default sort order by AddedDate.

answered Jan 25 '12 at 14:45

BrokenGlass

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I think the OP wants to be able to choose the sort key dynamically at runtime, so a Func won't work in this case... – Thomas Levesque Jan 25 '12 at 14:47
@ThomasLevesque: That's not how I read the question, but of course I might be wrong- leaving this up until OP can clarify. – BrokenGlass Jan 25 '12 at 14:50
@Thomas - that is exactly what I want to do. – Sachin Kainth Jan 25 '12 at 14:54

score 1 · Answer 2 · answered Jan 25 '12 at 14:45

1

Your best bet is to use Dynamic Linq. It allows you to pass the sort key as a string:

query.OrderByDescending(sort)...

answered Jan 25 '12 at 14:45

Thomas Levesque

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Copy the DynamicQuery.cs file from Visual Studio samples into your project, add a `using System.Linq.Dynamic;` in your code, and you're good to go ; you will see the new OrderBy overloads in intellisense – Thomas Levesque Jan 25 '12 at 15:09
I searched, I don't have DynamicQuery on my computer and even if I did, not sure how it would help. – Sachin Kainth Jan 25 '12 at 15:26
@Sachin, did you read the link I posted? It explains where you can download the samples, and where you can find the file in the samples. – Thomas Levesque Jan 25 '12 at 15:28

Passing a field to a function to sort on that field

2 Answers2