c# - Linq-to-Entities 动态排序

Question

这是我的查询，如何使用字符串作为 orderby 参数？

string sortColumn="Title";

var  items = (from ltem in ctxModel.Items
              where ltem.ItemID == vId
              orderby //something here
              select ltem).Skip(PageSize * PageIndex).Take(PageSize);

更新:
我不能只对结果集进行排序，因为我首先需要排序，然后才然后进行分页。

Answer 1

我使用这个助手:

public static class OrderExt
{
    private static IOrderedQueryable<T> Order<T>(this IQueryable<T> source, string propertyName, SortDirection descending, bool anotherLevel = false)
    {
        var param = Expression.Parameter(typeof(T), string.Empty);
        var property = Expression.PropertyOrField(param, propertyName);
        var sort = Expression.Lambda(property, param);

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

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

调用助手，例如这样做:

string sort = HttpContext.Current.Request.QueryString["sort"];
var products = _productRepository.OrderBy(sort, SortDirection.Ascending);