EF 分页查询优化

按照通常的方式分页查询至少要查询数据两遍，一个操作是查询总数，另一个是查询数据，这样有些耗时

这里介绍一个基于EF的插件 EntityFramework.Extended，当然这个插件有很多的功能，比方说批量删除、批量修改、批量查询、缓存查询等

这里只介绍批量查询的方法

通过SQL Server Profilter监视生成的SQL代码，发现只连接了一次数据库，非常的厉害

不解释直接上代码

通用分页查询方法：

         /// <summary>
         /// 分页查询
         /// </summary>
         /// <typeparam name="TKey">排序类型</typeparam>
         /// <param name="pageIndex">当前页</param>
         /// <param name="pageSize">每页大小</param>
         /// <param name="isAsc">是否升序排列</param>
         /// <param name="predicate">条件表达式</param>
         /// <param name="keySelector">排序表达式</param>
         /// <returns></returns>
         public virtual IPage<TEntity> Page<TKey>(int pageIndex, int pageSize, Expression<Func<TEntity, bool>> predicate, bool isAsc,
             Expression<Func<TEntity, TKey>> keySelector)
         {
             if (pageIndex <=  && pageSize <= )
             {
                 throw new Exception("pageIndex或pageSize不能小于等于0！");
             }
             IPage<TEntity> page = new Page<TEntity>()
             {
                 PageIndex = pageIndex,
                 PageSize = pageSize
             };
             int skip = (pageIndex - ) * pageSize;
             if (predicate == null)
             {
                 FutureCount fcount = this.dbSet.FutureCount();
                 FutureQuery<TEntity> futureQuery = isAsc
                     ? this.dbSet.OrderBy(keySelector).Skip(skip).Take(pageSize).Future()
                     : this.dbSet.OrderByDescending(keySelector).Skip(skip).Take(pageSize).Future();
                 page.TotalItems = fcount.Value;
                 page.Items = futureQuery.ToList();
                 page.TotalPages = page.TotalItems / pageSize;
                 if ((page.TotalItems % pageSize) != ) page.TotalPages++;
             }
             else
             {
                 var queryable = this.dbSet.Where(predicate);
                 FutureCount fcount = queryable.FutureCount();
                 FutureQuery<TEntity> futureQuery = isAsc
                     ? queryable.OrderBy(keySelector).Skip(skip).Take(pageSize).Future()
                     : queryable.OrderByDescending(keySelector).Skip(skip).Take(pageSize).Future();
                 page.TotalItems = fcount.Value;
                 page.Items = futureQuery.ToList();
                 page.TotalPages = page.TotalItems / pageSize;
                 if ((page.TotalItems % pageSize) != ) page.TotalPages++;
             }
             return page;
         }

分页实体：

     /// <summary>
     /// 分页实体
     /// </summary>
     /// <typeparam name="T">实体</typeparam>
     public class Page<T> : IPage<T>
     {
         /// <summary>
         /// 当前页
         /// </summary>
         public int PageIndex { get; set; }
         /// <summary>
         /// 总页数
         /// </summary>
         public int TotalPages { get; set; }
         /// <summary>
         /// 查询集合总个数
         /// </summary>
         public int TotalItems { get; set; }
         /// <summary>
         /// 每页项数
         /// </summary>
         public int PageSize { get; set; }
         /// <summary>
         /// 查询集合
         /// </summary>
         public IList<T> Items { get; set; }
     }

     /// <summary>
     /// 分页实体接口
     /// </summary>
     /// <typeparam name="T">实体</typeparam>
     public interface IPage<T>
     {
         /// <summary>
         /// 当前页
         /// </summary>
         int PageIndex { get; set; }
         /// <summary>
         /// 总页数
         /// </summary>
         int TotalPages { get; set; }
         /// <summary>
         /// 查询集合总个数
         /// </summary>
         int TotalItems { get; set; }
         /// <summary>
         /// 每页项数
         /// </summary>
         int PageSize { get; set; }
         /// <summary>
         /// 查询集合
         /// </summary>
         IList<T> Items { get; set; }
     }