LinqHelper

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace Helper
{
    /// <summary>
    /// 查询语句帮助类
    /// </summary>
    public static class LinqHelper
    {


        /// <summary>
        /// 动态排序
        /// </summary>
        /// <typeparam name="T">实体类型</typeparam>
        /// <param name="source">数据源</param>
        /// <param name="sortExpression">排序字段</param>
        /// <param name="sortDirection">排序方式</param>
        /// <returns></returns>
        public static IQueryable<T> DataSorting<T>(IQueryable<T> source, string sortExpression, string sortDirection)
        {
            string sortingDir = string.Empty;
            if (sortDirection.ToUpper().Trim() == "ASC")
                return source.OrderBy(a => typeof(T).GetProperty(sortExpression).GetValue(a, null));
            else 
                return source.OrderByDescending(a => typeof(T).GetProperty(sortExpression).GetValue(a, null));
        }
        /// <summary>
        /// 动态排序旧方法
        /// </summary>
        /// <typeparam name="T">实体类型</typeparam>
        /// <param name="source">数据源</param>
        /// <param name="sortExpression">排序字段</param>
        /// <param name="sortDirection">排序方式</param>
        /// <returns></returns>
        public static IQueryable<T> DataSorting1<T>(IQueryable<T> source, string sortExpression, string sortDirection)
        {
            string sortingDir = string.Empty;
            if (sortDirection.ToUpper().Trim() == "ASC")
                sortingDir = "OrderBy";
            else if (sortDirection.ToUpper().Trim() == "DESC")
                sortingDir = "OrderByDescending";
            ParameterExpression param = Expression.Parameter(typeof(T), sortExpression);
            PropertyInfo pi = typeof(T).GetProperty(sortExpression);
            Type[] types = new Type[2];
            types[0] = typeof(T);
            types[1] = pi.PropertyType;
            Expression expr = Expression.Call(typeof(Queryable), sortingDir, types, source.Expression, Expression.Lambda(Expression.Property(param, sortExpression), param));
            IQueryable<T> query = source.AsQueryable().Provider.CreateQuery<T>(expr);
            return query;
        }
        /// <summary>
        /// 分页
        /// </summary>
        /// <typeparam name="T">实体类型</typeparam>
        /// <param name="source">数据源</param>
        /// <param name="pageIndex">分页页码从第一页开始</param>
        /// <param name="pageSize">页码</param>
        /// <returns></returns>
        public static IQueryable<T> DataPaging<T>(IQueryable<T> source, int pageIndex, int pageSize)
        {
            return source.Skip((pageIndex-1) * pageSize).Take(pageSize);
        }
        /// <summary>
        /// 排序并分页
        /// </summary>
        /// <typeparam name="T">实体类型</typeparam>
        /// <param name="source">数据源</param>
        /// <param name="sortExpression">排序字段</param>
        /// <param name="sortDirection">排序方式</param>
        /// <param name="pageNumber">分页页码从第一页开始</param>
        /// <param name="pageSize">页码</param>
        /// <returns></returns>
        public static IQueryable<T> SortingAndPaging<T>(IQueryable<T> source, string sortExpression, string sortDirection, int pageNumber, int pageSize)
        {
            IQueryable<T> query = DataSorting<T>(source, sortExpression, sortDirection);
            return DataPaging(query, pageNumber, pageSize);
        }
    }
}