linq to sql中慎用Where(Func predicate)，小心被Linq给"骗"了! - 菩提树下的杨过 - 博客园

CREATE TABLE [dbo].[T_Test](
    [F_ID] [int] IDENTITY(1,1) NOT NULL,
    [F_Name] [nvarchar](50) COLLATE Chinese_PRC_CI_AS NULL,
    [F_Age] [int] NULL,
 CONSTRAINT [PK_T_Test] PRIMARY KEY CLUSTERED
(
    [F_ID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]

1using System;
2using System.Collections.Generic;
3using System.Linq;
4using System.Linq.Expressions;
5using CNTVS.LINQ;
6
7namespace TestLinq
8{
9    class Program
10    {
11        static void Main(string[] args)
12        {
13
14            //Expression<Func<T_Test, bool>> _Expression = PredicateBuilder.True<T_Test>();
15            //_Expression = _Expression.And(t => t.F_Age >= 20).And(t => t.F_Name.Contains(“J”));
16            //var Data = GetData(_Expression, 1, 1);
17
18            var Data = GetData(1, 1);
19
20            ShowData(Data);
21
22
23        }
24
25        /// <summary>
26        /// 用Where<T>(Expression)方式获取数据
27        /// </summary>
28        /// <param name=”ExpWhere”></param>
29        /// <param name=”PageSize”></param>
30        /// <param name=”CurrentPageIndex”></param>
31        /// <returns></returns>
32        static List<T_Test> GetData(Expression<Func<T_Test,bool>> ExpWhere,int PageSize,int CurrentPageIndex)
33        {
34            List<T_Test> _Result = null;
35            using (DBDataContext db = new DBDataContext())
36            {
37                try
38                {
39                    var query = db.T_Test.Where<T_Test>(ExpWhere.Compile()).Skip((CurrentPageIndex – 1) * PageSize).Take(PageSize);
40                    _Result = query.ToList();
41                }
42                finally { db.Connection.Close(); }
43            }
44            return _Result;
45        }
46
47
48        /// <summary>
49        /// 用Where(Lambda)方式获取数据
50        /// </summary>
51        /// <param name=”PageSize”></param>
52        /// <param name=”CurrentPageIndex”></param>
53        /// <returns></returns>
54        static List<T_Test> GetData(int PageSize, int CurrentPageIndex)
55        {
56            List<T_Test> _Result = null;
57            using (DBDataContext db = new DBDataContext())
58            {
59                try
60                {
61                    var query = db.T_Test.Where(t => t.F_Age >= 20 && t.F_Name.Contains(“J”)).Skip((CurrentPageIndex – 1) * PageSize).Take(PageSize);
62                    _Result = query.ToList();
63                }
64                finally { db.Connection.Close(); }
65            }
66            return _Result;
67        }
68
69
70        /// <summary>
71        /// 显示数据
72        /// </summary>
73        /// <param name=”Data”></param>
74        static void ShowData(List<T_Test> Data)
75        {
76            foreach (var item in Data)
77            {
78                Console.WriteLine(“Name:{0}\t，Age:{1}”, item.F_Name, item.F_Age.ToString());
79            }
80            Console.ReadKey();
81        }
82    }
83}

exec sp_executesql N’SELECT [t1].[F_ID], [t1].[F_Name], [t1].[F_Age]
FROM (
    SELECT ROW_NUMBER() OVER (ORDER BY [t0].[F_ID], [t0].[F_Name], [t0].[F_Age]) AS [ROW_NUMBER], [t0].[F_ID], [t0].[F_Name], [t0].[F_Age]
    FROM [dbo].[T_Test] AS [t0]
    WHERE ([t0].[F_Age] >= @p0) AND ([t0].[F_Name] LIKE @p1)
    ) AS [t1]
WHERE [t1].[ROW_NUMBER] BETWEEN @p2 + 1 AND @p2 + @p3
ORDER BY [t1].[ROW_NUMBER]’,N’@p0 int,@p1 nvarchar(3),@p2 int,@p3 int’,@p0=20,@p1=N’%J%’,@p2=1,@p3=1

1static void Main(string[] args)
2        {
3            Expression<Func<T_Test, bool>> _Expression = PredicateBuilder.True<T_Test>();
4            _Expression = _Expression.And(t => t.F_Age >= 20).And(t => t.F_Name.Contains(“J”));
5            var Data = GetData(_Expression, 1, 1);
6
7            //var Data = GetData(1, 2);
8
9            ShowData(Data);
10        }

SELECT [t0].[F_ID], [t0].[F_Name], [t0].[F_Age]
FROM [dbo].[T_Test] AS [t0]