CODEWITHSUNDEEP
c#linq-to-entities
Sergio Tapia
Sergio Tapia

Reputation: 41158

The method 'Skip' is only supported for sorted input in LINQ to Entities

What could be causing this problem?

public ActionResult Index(int page = 0)
{
    const int pageSize = 3;
    var areas = repo.FindAllAreas();
    var paginatedArea = new PaginatedList<Area>(areas, page, pageSize);

    return View(paginatedArea);
}


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace UTEPSA.Controllers
{
    class PaginatedList<T> : List<T>
    {
        public int PageIndex { get; private set; }
        public int PageSize { get; private set; }
        public int TotalCount { get; private set; }
        public int TotalPages { get; private set; }
        public PaginatedList(IQueryable<T> source, int pageIndex, int pageSize)
        {
            PageIndex = pageIndex;
            PageSize = pageSize;
            TotalCount = source.Count();
            TotalPages = (int)Math.Ceiling(TotalCount / (double)PageSize);
//ERROR HERE->>this.AddRange(source.Skip(PageIndex * PageSize).Take(PageSize));
        }
        public bool HasPreviousPage
        {
            get
            {
                return (PageIndex > 0);
            }
        }
        public bool HasNextPage
        {
            get
            {
                return (PageIndex + 1 < TotalPages);
            }
        }
    }
}

Any suggestions?

Upvotes: 22

Views: 45417

Answers (4)

Wagner Silveira
Wagner Silveira

Reputation: 1626

Seems like the error is exactly what it is says. "Skip is only allowed on Sorted inputs". Searching for this error, I've found this.

It should be fixed if you include an OrderBy before Skip:

source.orderBy(???).Skip(PageIndex * PageSize).Take(PageSize));

Which might be a problem since you are passing a generic object T. You might need to expand your class to receive another parameter to indicate the order by element.

Upvotes: 33

Peter Shen
Peter Shen

Reputation: 147

I wanted to validate this by running the SQL equivalent of a similar LINQ skip/take query.

SELECT * FROM [table]
--order by [column] //omitted!
OFFSET 10 ROWS
FETCH NEXT 15 rows only

Note that when the order-by clause is omitted, the SQL error is much less informative:

"Invalid usage of the option NEXT in the FETCH statement."

So the "sorted input" is actually required on the database-level. Kudos to LINQ for helping developers write advanced SQL statements!

Upvotes: 2

mavore
mavore

Reputation: 39

that is worked (use first IOrderedQueryable):

http://msdn.microsoft.com/en-us/library/bb738702.aspx

 IOrderedQueryable<Product> products = context.Products
        .OrderBy(p => p.ListPrice);

IQueryable<Product> allButFirst3Products = products.Skip(3);

Console.WriteLine("All but first 3 products:");
foreach (Product product in allButFirst3Products)
{
    Console.WriteLine("Name: {0} \t ID: {1}",
        product.Name,
        product.ProductID);
}

Upvotes: 3

Zooba
Zooba

Reputation: 11438

An IQueryable does not have an order, so saying "ignore the next x elements" doesn't make any sense.

If you include an order by clause (or possibly an AsEnumerable() call - untested) then your data takes an order and Skip and Take are now sensible.

Upvotes: 2

Related Questions