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：
1 /// <summary>
2 /// 分页查询
3 /// </summary>
4 /// <typeparam name="TKey">排序类型</typeparam>
5 /// <param name="pageIndex">当前页</param>
6 /// <param name="pageSize">每页大小</param>
7 /// <param name="isAsc">是否升序排列</param>
8 /// <param name="predicate">条件表达式</param>
9 /// <param name="keySelector">排序表达式</param>
10 /// <returns></returns>
11 public virtual IPage<TEntity> Page<TKey>(int pageIndex, int pageSize, Expression<Func<TEntity, bool>> predicate, bool isAsc,
12 Expression<Func<TEntity, TKey>> keySelector)
13 {
14 if (pageIndex <= 0 && pageSize <= 0)
15 {
16 throw new Exception("pageIndex或pageSize不能小于等于0！");
17 }
18 IPage<TEntity> page = new Page<TEntity>()
19 {
20 PageIndex = pageIndex,
21 PageSize = pageSize
22 };
23 int skip = (pageIndex - 1) * pageSize;
24 if (predicate == null)
25 {
26 FutureCount fcount = this.dbSet.FutureCount();
27 FutureQuery<TEntity> futureQuery = isAsc
28 ? this.dbSet.OrderBy(keySelector).Skip(skip).Take(pageSize).Future()
29 : this.dbSet.OrderByDescending(keySelector).Skip(skip).Take(pageSize).Future();
30 page.TotalItems = fcount.Value;
31 page.Items = futureQuery.ToList();
32 page.TotalPages = page.TotalItems / pageSize;
33 if ((page.TotalItems % pageSize) != 0) page.TotalPages++;
34 }
35 else
36 {
37 var queryable = this.dbSet.Where(predicate);
38 FutureCount fcount = queryable.FutureCount();
39 FutureQuery<TEntity> futureQuery = isAsc
40 ? queryable.OrderBy(keySelector).Skip(skip).Take(pageSize).Future()
41 : queryable.OrderByDescending(keySelector).Skip(skip).Take(pageSize).Future();
42 page.TotalItems = fcount.Value;
43 page.Items = futureQuery.ToList();
44 page.TotalPages = page.TotalItems / pageSize;
45 if ((page.TotalItems % pageSize) != 0) page.TotalPages++;
46 }
47 return page;
48 }
分页实体：
1 /// <summary>
2 /// 分页实体
3 /// </summary>
4 /// <typeparam name="T">实体</typeparam>
5 public class Page<T> : IPage<T>
6 {
7 /// <summary>
8 /// 当前页
9 /// </summary>
10 public int PageIndex { get; set; }
11 /// <summary>
12 /// 总页数
13 /// </summary>
14 public int TotalPages { get; set; }
15 /// <summary>
16 /// 查询集合总个数
17 /// </summary>
18 public int TotalItems { get; set; }
19 /// <summary>
20 /// 每页项数
21 /// </summary>
22 public int PageSize { get; set; }
23 /// <summary>
24 /// 查询集合
25 /// </summary>
26 public IList<T> Items { get; set; }
27 }
28
29 /// <summary>
30 /// 分页实体接口
31 /// </summary>
32 /// <typeparam name="T">实体</typeparam>
33 public interface IPage<T>
34 {
35 /// <summary>
36 /// 当前页
37 /// </summary>
38 int PageIndex { get; set; }
39 /// <summary>
40 /// 总页数
41 /// </summary>
42 int TotalPages { get; set; }
43 /// <summary>
44 /// 查询集合总个数
45 /// </summary>
46 int TotalItems { get; set; }
47 /// <summary>
48 /// 每页项数
49 /// </summary>
50 int PageSize { get; set; }
51 /// <summary>
52 /// 查询集合
53 /// </summary>
54 IList<T> Items { get; set; }
55 }