public static class QueryableExtensions{#region 内存分页/// <summary>/// 返回对象分页列表/// </summary>/// <typeparam name="T">对象类型</typeparam>/// <param name="dataSource">已排序的数据源</param>/// <param name="pageIndex">页码，1开始</param>/// <param name="pageSize">页条数</param>/// <returns>对象分页列表</returns>public static IPagedList<T> ToPagedList<T>(this IList<T> dataSource, int pageIndex, int pageSize)where T : class{pageIndex = pageIndex <= 0 ? 1 : pageIndex;var pagedList = new PagedList<T>{PageIndex = pageIndex,PageSize = pageSize,TotalCount = dataSource.Count,Entities = dataSource.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList()};return pagedList;}/// <summary>/// 返回对象分页列表/// </summary>/// <typeparam name="T">对象类型</typeparam>/// <param name="dataSource">已排序的数据源</param>/// <param name="pager">分页器对象；当为空时，分页器取默认值</param>/// <returns>对象分页列表</returns>public static IPagedList<T> ToPagedList<T>(this IList<T> dataSource, Pager pager) where T : class{pager = pager ?? new Pager();return dataSource.ToPagedList(pager.PageIndex, pager.PageSize);}#endregion#region IQueryable分页/// <summary>/// 返回对象分页列表/// </summary>/// <typeparam name="T">对象类型</typeparam>/// <param name="dataSource">已排序的数据源</param>/// <param name="pageIndex">页码，1开始</param>/// <param name="pageSize">页条数</param>/// <returns>对象分页列表</returns>public static IPagedList<T> ToPagedList<T>(this IQueryable<T> dataSource, int pageIndex, int pageSize)where T : class{pageIndex = pageIndex <= 0 ? 1 : pageIndex;var pagedList = new PagedList<T>{PageIndex = pageIndex,PageSize = pageSize,TotalCount = dataSource.Count(),Entities = dataSource.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList()};return pagedList;}/// <summary>/// 返回对象分页列表/// </summary>/// <typeparam name="T">对象类型</typeparam>/// <param name="dataSource">已排序的数据源</param>/// <param name="pager">分页器对象；当为空时，分页器取默认值</param>/// <returns>对象分页列表</returns>public static IPagedList<T> ToPagedList<T>(this IQueryable<T> dataSource, Pager pager) where T : class{pager = pager ?? new Pager();return dataSource.ToPagedList(pager.PageIndex, pager.PageSize);}#endregion/// <summary>/// 当满足特定条件时执行查询/// </summary>/// <typeparam name="T">对象类型</typeparam>/// <param name="source">查询对象</param>/// <param name="condition">需要满足的条件</param>/// <param name="predicate">满足条件时执行的查询表达式</param>/// <returns>结果集</returns>public static IQueryable<T> WhereIf<T>(this IQueryable<T> source, bool condition,Expression<Func<T, bool>> predicate){return condition ? source.Where(predicate) : source;}}

 /// <summary>/// 分页器/// </summary>public class Pager{/// <summary>/// 分页索引（默认为1）/// </summary>public int PageIndex { get; set; } = 1;/// <summary>/// 分页大小（默认为10）/// </summary>public int PageSize { get; set; } = 10;}