Lambda动态排序分页通用方法

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

namespace Common
{
public class QueryParameters
{
public QueryParameters();

public string order { get; set; }
public int page { get; set; }
public int rows { get; set; }
public string sort { get; set; }
}

public class DataGrid<T>
{
/// <summary>
/// 默认构造函数
/// </summary>
public DataGrid() { }

/// <summary>
/// 构造函数
/// </summary>
/// <param name="rows">表格数据</param>
public DataGrid(List<T> rows)
{
this.rows = rows;
}
private List<T> _rows = new List<T>();

/// <summary>
/// 表格数据
/// </summary>
public List<T> rows
{
get { return _rows; }
set
{
if (value != null)
{
_rows = value;
}
}
}

/// <summary>
/// 总记录数
/// </summary>
public int total { get; set; }

public static DataGrid<T> QueryWithParameters(IEnumerable<T> queryable, QueryParameters queryParameters)
{
if (queryable == null)
{
return new DataGrid<T>();
}
queryParameters = queryParameters ?? new QueryParameters();
IQueryable<T> source = Queryable.AsQueryable<T>(queryable);

var page = queryParameters.page;
var rows = queryParameters.rows;
var sort = queryParameters.sort;
var order = queryParameters.order;

int num = source.Count();

int count = (page - 1) * rows;

IQueryable<T> s = source;

if (!string.IsNullOrWhiteSpace(sort))
{
var sortExpression = Expression.Parameter(source.ElementType);
var selector = Expression.Lambda(Expression.PropertyOrField(sortExpression, sort), sortExpression);
if (order.ToLower() == "asc")
{
s = (IQueryable<T>)source.Provider.CreateQuery(Expression.Call(typeof(Queryable), "OrderBy", new Type[] { source.ElementType, selector.Body.Type }, source.Expression, selector));
}
else if (order.ToLower() == "desc")
{
s = (IQueryable<T>)source.Provider.CreateQuery(Expression.Call(typeof(Queryable), "OrderByDescending", new Type[] { source.ElementType, selector.Body.Type }, source.Expression, selector));
}
}

//方法1
s = count == 0 ? s.Take(rows) : s.Skip(count).Take(rows);
//方法2
s = count == 0 ? Queryable.Take<T>(s, rows) : Queryable.Take<T>(Queryable.Skip<T>(s, count), rows);

return new DataGrid<T>()
{
total = num,
rows = s.ToList()
};
}
}
}

DataGrid<T>.QueryWithParameters(query, paging)