生成动态Lambda表达式1

SqlDataReader生成动态Lambda表达式

上一扁使用动态lambda表达式来将DataTable转换成实体，比直接用反射快了不少。主要是首行转换的时候动态生成了委托。

后面的转换都是直接调用委托，省去了多次用反射带来的性能损失。

今天在对SqlServer返回的流对象 SqlDataReader 进行处理，也采用动态生成Lambda表达式的方式转换实体。

先上一版代码

 1 using System;

 2 using System.Collections.Generic;

 3 using System.Data;

 4 using System.Data.Common;

 5 using System.Data.SqlClient;

 6 using System.Linq;

 7 using System.Linq.Expressions;

 8 using System.Reflection;

 9 using System.Text;

10 using System.Threading.Tasks;

11

12 namespace Demo1

13 {

14     public static class EntityConverter

15     {

16         #region

17         /// <summary>

18         /// DataTable生成实体

19         /// </summary>

20         /// <typeparam name="T"></typeparam>

21         /// <param name="dataTable"></param>

22         /// <returns></returns>

23         public static List<T> ToList<T>(this DataTable dataTable) where T : class, new()

24         {

25             if (dataTable == null || dataTable.Rows.Count <= 0) throw new ArgumentNullException("dataTable", "当前对象为null无法生成表达式树");

26             Func<DataRow, T> func = dataTable.Rows[0].ToExpression<T>();

27             List<T> collection = new List<T>(dataTable.Rows.Count);

28             foreach (DataRow dr in dataTable.Rows)

29             {

30                 collection.Add(func(dr));

31             }

32             return collection;

33         }

34

35

36         /// <summary>

37         /// 生成表达式

38         /// </summary>

39         /// <typeparam name="T"></typeparam>

40         /// <param name="dataRow"></param>

41         /// <returns></returns>

42         public static Func<DataRow, T> ToExpression<T>(this DataRow dataRow) where T : class, new()

43         {

44             if (dataRow == null) throw new ArgumentNullException("dataRow", "当前对象为null 无法转换成实体");

45             ParameterExpression parameter = Expression.Parameter(typeof(DataRow), "dr");

46             List<MemberBinding> binds = new List<MemberBinding>();

47             for (int i = 0; i < dataRow.ItemArray.Length; i++)

48             {

49                 String colName = dataRow.Table.Columns[i].ColumnName;

50                 PropertyInfo pInfo = typeof(T).GetProperty(colName);

51                 if (pInfo == null || !pInfo.CanWrite) continue;

52                 MethodInfo mInfo = typeof(DataRowExtensions).GetMethod("Field", new Type[] { typeof(DataRow), typeof(String) }).MakeGenericMethod(pInfo.PropertyType);

53                 MethodCallExpression call = Expression.Call(mInfo, parameter, Expression.Constant(colName, typeof(String)));

54                 MemberAssignment bind = Expression.Bind(pInfo, call);

55                 binds.Add(bind);

56             }

57             MemberInitExpression init = Expression.MemberInit(Expression.New(typeof(T)), binds.ToArray());

58             return Expression.Lambda<Func<DataRow, T>>(init, parameter).Compile();

59         }

60         #endregion

61         /// <summary>

62         /// 生成lambda表达式

63         /// </summary>

64         /// <typeparam name="T"></typeparam>

65         /// <param name="reader"></param>

66         /// <returns></returns>

67         public static Func<SqlDataReader, T> ToExpression<T>(this SqlDataReader reader) where T : class, new()

68         {

69             if (reader == null || reader.IsClosed || !reader.HasRows) throw new ArgumentException("reader", "当前对象无效");

70             ParameterExpression parameter = Expression.Parameter(typeof(SqlDataReader), "reader");

71             List<MemberBinding> binds = new List<MemberBinding>();

72             for (int i = 0; i < reader.FieldCount; i++)

73             {

74                 String colName = reader.GetName(i);

75                 PropertyInfo pInfo = typeof(T).GetProperty(colName);

76                 if (pInfo == null || !pInfo.CanWrite) continue;

77                 MethodInfo mInfo = reader.GetType().GetMethod("GetFieldValue").MakeGenericMethod(pInfo.PropertyType);

78                 MethodCallExpression call = Expression.Call(parameter, mInfo, Expression.Constant(i));

79                 MemberAssignment bind = Expression.Bind(pInfo, call);

80                 binds.Add(bind);

81             }

82             MemberInitExpression init = Expression.MemberInit(Expression.New(typeof(T)), binds.ToArray());

83             return Expression.Lambda<Func<SqlDataReader, T>>(init, parameter).Compile();

84         }

85

86     }

87 }

在上一篇的基础上增加了 SqlDataReader 的扩展方法

以下代码是调用

 1 using System;

 2 using System.Collections.Generic;

 3 using System.Data;

 4 using System.Data.Common;

 5 using System.Data.SqlClient;

 6 using System.Diagnostics;

 7 using System.Linq;

 8 using System.Reflection;

 9 using System.Text;

10 using System.Threading.Tasks;

11

12 namespace Demo1

13 {

14     class Program

15     {

16         static void Main(string[] args)

17         {

18             String conString = "Data Source=.; Initial Catalog=master; Integrated Security=true;";

19             Func<SqlDataReader, Usr> func = null;

20             List<Usr> usrs = new List<Usr>();

21             using (SqlDataReader reader = GetReader(conString, "select object_id 'ID',name 'Name' from sys.objects", CommandType.Text, null))

22             {

23                 while (reader.Read())

24                 {

25                     if (func == null)

26                     {

27                         func = reader.ToExpression<Usr>();

28                     }

29                     Usr usr = func(reader);

30                     usrs.Add(usr);

31                 }

32             }

33             usrs.Clear();

34             Console.ReadKey();

35         }

36

37         public static SqlDataReader GetReader(String conString, String sql, CommandType type, params SqlParameter[] pms)

38         {

39             SqlConnection conn = new SqlConnection(conString);

40             SqlCommand cmd = new SqlCommand(sql, conn);

41             cmd.CommandType = type;

42             if (pms != null && pms.Count() > 0)

43             {

44                 cmd.Parameters.AddRange(pms);

45             }

46             conn.Open();

47             return cmd.ExecuteReader(CommandBehavior.CloseConnection);

48         }

49     }

50     class Usr

51     {

52         public Int32 ID { get; set; }

53         public String Name { get; set; }

54     }

55

56

57 }

目前只能处理sqlserver返回的对象，处理其它数据库本来是想增加 DbDataReader 的扩展方法，但发现动态生成lambda表达式的地方出错，所以先将现在的

巴特西

生成动态Lambda表达式1

SqlDataReader生成动态Lambda表达式

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