Unable to sort with property name in LINQ OrderBy

问题:

Error is

LINQ to Entities does not recognize the method 'System.Object GetValue(System.Object, System.Object[])' method, and this method cannot be translated into a store expression.

My code is

public static GridResult GetAllUsers(int count, int tblsize,string sortcreteria)
{
      using (UserEntities entity = new UserEntities())
      {

          var data = entity.User_Details.Take(count)
.OrderBy(i =>.GetType().GetProperty(sortcreteria).GetValue(i,null))
.Skip(tblsize).ToList();
          result.DataSource = data;
          result.Count = entity.User_Details.Count();
      }
      return result;
}

How to sort with property name as string?

回答1:

Just add the following extension to your code and you're good to go:

using System.Linq;
using System.Linq.Expressions;
using System;

namespace SomeNameSpace
{
    public static class SomeExtensionClass
    {
        public static IQueryable<T> OrderByField<T>(this IQueryable<T> q, string SortField, bool Ascending)
        {
            var param = Expression.Parameter(typeof(T), "p");
            var prop = Expression.Property(param, SortField);
            var exp = Expression.Lambda(prop, param);
            string method = Ascending ? "OrderBy" : "OrderByDescending";
            Type[] types = new Type[] { q.ElementType, exp.Body.Type };
            var mce = Expression.Call(typeof(Queryable), method, types, q.Expression, exp);
            return q.Provider.CreateQuery<T>(mce);
        }
    }

}

Usage:

.OrderByField(sortcriteria, true)

Edit:

For support for the ThenBy method however the following methods returning an IOrderedQueryable should take care of it all:

public static class SomeExtensionClass
{
    private static IOrderedQueryable<T> OrderingHelper<T>(IQueryable<T> source, string propertyName, bool descending, bool anotherLevel)
    {
        var param = Expression.Parameter(typeof(T), "p");
        var property = Expression.PropertyOrField(param, propertyName);
        var sort = Expression.Lambda(property, param);

        var call = Expression.Call(
            typeof(Queryable),
            (!anotherLevel ? "OrderBy" : "ThenBy") + (descending ? "Descending" : string.Empty),
            new[] { typeof(T), property.Type },
            source.Expression,
            Expression.Quote(sort));

        return (IOrderedQueryable<T>)source.Provider.CreateQuery<T>(call);
    }

    public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string propertyName)
    {
        return OrderingHelper(source, propertyName, false, false);
    }

    public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string propertyName, bool descending)
    {
        return OrderingHelper(source, propertyName, descending, false);
    }

    public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string propertyName)
    {
        return OrderingHelper(source, propertyName, false, true);
    }

    public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string propertyName, bool descending)
    {
        return OrderingHelper(source, propertyName, descending, true);
    }
}

回答2:

You could try to do this using the (somewhat old) Dynamic LINQ library:

var data = entity.User_Details
    .Take(count)
    .OrderBy(sortcriteria)
    .Skip(tblsize)
    .ToList();

Alternatively, you can still sort the sequence using your original query by moving the objects into memory first, since the LINQ to Entities provider can't translate calls to the Reflection API into SQL:

var data = entity.User_Details
    .Take(count)
    .Skip(tblsize)
    .AsEnumerable()
    .OrderBy(i => i.GetType().GetProperty(sortcriteria).GetValue(i, null))

回答3:

You will probably need to use Expression Trees to construct the Linq statement OrderBy(x => x.SomeProperty).

Create an OrderBy Expression for LINQ/Lambda

Create LINQ to entities OrderBy expression on the fly