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在使用EF的过程有很多需要分页查询数据的地方，但是经常重复在输入分页的相关代码，这样即不便于维护，也增加了不少工作量。

对于通用查询有几个要点，一是要动态定义查询条件，还可以动态选择所需要的列。

1、数据查询方法

Code Snippet

1. publicstaticList<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query,
2.                                                                       Expression<Func<TEntity, bool>> where,
3.                                                                       Expression<Func<TEntity, TOrderBy>> orderby,
4.                                                                       Expression<Func<TEntity, int, TResult>> selector,
5.                                                                       bool isAsc)

Code Snippet

1. publicstaticList<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query,
2.                                                                       Expression<Func<TEntity, bool>> where,
3.                                                                       Expression<Func<TEntity, TOrderBy>> orderby,
4.                                                                       Func<IQueryable<TEntity>, List<object>> selector,
5.                                                                       bool isAsc)

Code Snippet

1. publicstaticPageInfo<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query, int index, int pageSize,
2.                                                                 Expression<Func<TEntity, bool>> where,
3.                                                                 Expression<Func<TEntity, TOrderBy>> orderby,
4.                                                                 Func<IQueryable<TEntity>, List<object>> selector,
5.                                                                 bool isAsc)

3、分页查询方法

Code Snippet

1. publicstaticPageInfo<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query, int index, int pageSize,
2.                                                          List<Expression<Func<TEntity, bool>>> wheres,
3.                                                          Expression<Func<TEntity, TOrderBy>> orderby,
4.                                                          Func<IQueryable<TEntity>, List<object>> selector, bool isAsc)

Code Snippet

1. publicstaticPageInfo<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query, int index, int pageSize,
2.                                                          List<Expression<Func<TEntity, bool>>> wheres,
3.                                                          Expression<Func<TEntity, TOrderBy>> orderby,
4.                                                          Func<IQueryable<TEntity>, List<TResult>> selector, bool isAsc)

Code Snippet

1. publicstaticPageInfo<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query, int index, int pageSize,
2.                                                                 Expression<Func<TEntity, bool>> where,
3.                                                                 Expression<Func<TEntity, TOrderBy>> orderby,
4.                                                                 Func<IQueryable<TEntity>, List<TResult>> selector,
5.                                                                 bool isAsc)

工具类方法：

Code Snippet

1. publicclassPageInfo
2.     {
3.         publicstaticvoid CheckPageIndexAndSize(refint index, refint size)
4.         {
5.             if (index < 1)
6.             {
7.                 index = 1;
8.             }
9.  
10.             if (size < 1)
11.             {
12.                 size = 20;
13.             }
14.         }
15.  
16.         publicstaticvoid CheckPageIndexAndSize(refint index, int size, int count)
17.         {
18.             if (count >= index * size)
19.             {
20.                 return;
21.             }
22.  
23.             index = count / size;
24.             if (count % size > 0)
25.             {
26.                 index++;
27.             }
28.  
29.             if (index == 0)
30.             {
31.                 index = 1;
32.             }
33.         }
34.  
35.     }
36.  
37.     publicclassPageInfo<T> : PageInfo
38.     {
39.         internal PageInfo()
40.         {
41.             DataList = newList<T>();
42.         }
43.         public PageInfo(int index, int pageSize, int count, List<T> dataList)
44.         {
45.             Index = index;
46.             PageSie = pageSize;
47.             Count = count;
48.             DataList = dataList;
49.         }
50.  
51.         publicint Index { get; privateset; }
52.         publicint PageSie { get; privateset; }
53.         publicint Count { get; privateset; }
54.         publicList<T> DataList { get; privateset; }
55.  
56.         publicPageInfo<T> Empty
57.         {
58.             get { returnnewPageInfo<T>(); }
59.         }
60.     }

实现代码：

Code Snippet

1. publicstaticclassLinqExtent
2.     {
3.         publicstaticList<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query,
4.                                                                       Expression<Func<TEntity, bool>> where,
5.                                                                       Expression<Func<TEntity, TOrderBy>> orderby,
6.                                                                       Expression<Func<TEntity, int, TResult>> selector,
7.                                                                       bool isAsc)
8.         {
9.             if (selector == null)
10.             {
11.                 thrownewArgumentNullException("selector");
12.             }
13.  
14.             var queryable = query;
15.             if (where != null)
16.             {
17.                 queryable = queryable.Where(where);
18.             }
19.             if (orderby != null)
20.             {
21.                 queryable = isAsc ? queryable.OrderBy(orderby) : queryable.OrderByDescending(orderby);
22.             }
23.  
24.             return queryable.Select(selector).ToList();
25.         }
26.  
27.         publicstaticList<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query,
28.                                                                       Expression<Func<TEntity, bool>> where,
29.                                                                       Expression<Func<TEntity, TOrderBy>> orderby,
30.                                                                       Func<IQueryable<TEntity>, List<object>> selector,
31.                                                                       bool isAsc)
32.         {
33.             if (selector == null)
34.             {
35.                 thrownewArgumentNullException("selector");
36.             }
37.  
38.             var queryable = query;
39.             if (where != null)
40.             {
41.                 queryable = queryable.Where(where);
42.             }
43.             if (orderby != null)
44.             {
45.                 queryable = isAsc ? queryable.OrderBy(orderby) : queryable.OrderByDescending(orderby);
46.             }
47.  
48.             return selector(queryable);
49.         }
50.  
51.         publicstaticPageInfo<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query, int index, int pageSize,
52.                                                                 Expression<Func<TEntity, bool>> where,
53.                                                                 Expression<Func<TEntity, TOrderBy>> orderby,
54.                                                                 Func<IQueryable<TEntity>, List<object>> selector,
55.                                                                 bool isAsc)
56.         {
57.             return Query(query, index, pageSize, newList<Expression<Func<TEntity, bool>>> {where}, orderby, selector,
58.                          isAsc);
59.         }
60.         publicstaticPageInfo<object> Query<TEntity, TOrderBy>(thisIQueryable<TEntity> query, int index, int pageSize,
61.                                                          List<Expression<Func<TEntity, bool>>> wheres,
62.                                                          Expression<Func<TEntity, TOrderBy>> orderby,
63.                                                          Func<IQueryable<TEntity>, List<object>> selector, bool isAsc)
64.         {
65.             //if (selector == null)
66.             //{
67.             //    throw new ArgumentNullException("selector");
68.             //}
69.  
70.             //PageInfo.CheckPageIndexAndSize(ref index,ref pageSize);
71.             //IQueryable<TEntity> queryable = query;
72.             //if (wheres != null)
73.             //{
74.             //    wheres.ForEach(p=>queryable = queryable.Where(p));
75.             //}
76.  
77.             //int count = query.Count();
78.             //PageInfo.CheckPageIndexAndSize(ref index,pageSize,count);
79.             //if (count > 0)
80.             //{
81.             //    if (orderby != null)
82.             //    {
83.             //        queryable = isAsc ? queryable.OrderBy(orderby) : queryable.OrderByDescending(orderby);
84.  
85.             //    }
86.  
87.             //    return new PageInfo<object>(index,pageSize,count,selector(queryable));
88.             //}
89.  
90.             //return new PageInfo<object>(index,pageSize,count,new List<object>());
91.  
92.             return Query<TEntity, TOrderBy, object>(query, index, pageSize, wheres, orderby, selector, isAsc);
93.         }
94.  
95.         publicstaticPageInfo<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query, int index, int pageSize,
96.                                                          List<Expression<Func<TEntity, bool>>> wheres,
97.                                                          Expression<Func<TEntity, TOrderBy>> orderby,
98.                                                          Func<IQueryable<TEntity>, List<TResult>> selector, bool isAsc)
99.         {
100.             if (selector == null)
101.             {
102.                 thrownewArgumentNullException("selector");
103.             }
104.  
105.             PageInfo.CheckPageIndexAndSize(ref index, ref pageSize);
106.             IQueryable<TEntity> queryable = query;
107.             if (wheres != null)
108.             {
109.                 wheres.ForEach(p => queryable = queryable.Where(p));
110.             }
111.  
112.             int count = query.Count();
113.             PageInfo.CheckPageIndexAndSize(ref index, pageSize, count);
114.             if (count > 0)
115.             {
116.                 if (orderby != null)
117.                 {
118.                     queryable = isAsc ? queryable.OrderBy(orderby) : queryable.OrderByDescending(orderby);
119.  
120.                 }
121.  
122.                 returnnewPageInfo<TResult>(index, pageSize, count, selector(queryable));
123.             }
124.  
125.             returnnewPageInfo<TResult>(index, pageSize, count, newList<TResult>());
126.         }
127.  
128.         publicstaticPageInfo<TResult> Query<TEntity, TOrderBy, TResult>(thisIQueryable<TEntity> query, int index, int pageSize,
129.                                                                 Expression<Func<TEntity, bool>> where,
130.                                                                 Expression<Func<TEntity, TOrderBy>> orderby,
131.                                                                 Func<IQueryable<TEntity>, List<TResult>> selector,
132.                                                                 bool isAsc)
133.         {
134.             return Query(query, index, pageSize, newList<Expression<Func<TEntity, bool>>> { where }, orderby, selector,
135.                          isAsc);
136.         }
137.     }