Variables in Select Statement

Question

I have the following function:

    public List<TopMediansModel> QueryForMedians(string state, string median)
    {
        ApplicationDbContext db = new ApplicationDbContext();
        return (from q in db.StateSuburbLocation
                where (q.State == state)
                orderby q.GetType().GetProperty(median) descending
                select new TopMediansModel
                {
                    Median = median,
                    MedianValue = q.GetType().GetProperty(median),
                    MedianSuburb = q.Suburb
                }).Take(10).ToList();
    }

Is it possible to have the orderby and MedianValue 'properties' as variables?

I've tried using the GetType().GetProperty() Methods, and am no doubt doing so incorrectly.

Sergey Berezovskiy · Accepted Answer · 2015-05-11 05:06:34Z

2

You can use something like Dynamic Linq

return db.StateSuburbLocation
         .Where(l => l.State == state)
         .OrderByDescending(median)
         .Select(l => new TopMediansModel {
             Median = median,
             MedianValue = q.GetType().GetProperty(median),
             MedianSuburb = q.Suburb
          }).Take(10).ToList();

Or you can build query expression manually

    public static IQueryable<T> OrderByDescending<T>(
        this IQueryable<T> source, string propertyName)
    {         
        var parameter = Expression.Parameter(typeof(T), "p");
        var property = Expression.PropertyOrField(parameter, propertyName);
        var keySelector = Expression.Lambda<Func<T, object>>(property, parameter);
        return source.OrderByDescending(keySelector);
    }

Usage is same

edited May 11, 2015 at 5:06

answered May 11, 2015 at 4:39

Sergey Berezovskiy

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2 Comments

user1470994 Over a year ago

Thanks for the feedback Sergey, I'd prefer not to use another reference as I'll only be doing this in one function. Could you explain what you mean by building the query expression manually?

user1470994 Over a year ago

Trying this I get the following error

Error	1	The type arguments for method 'System.Linq.Enumerable.OrderByDescending<TSource,TKey>(System.Collections.Generic.IEnumerable<TSource>, System.Func<TSource,TKey>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

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