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 Demo113 {14     public static class EntityConverter15     {16         #region17         /// 
18         /// DataTable生成实体19         /// 
20         /// 
     21         /// 22         /// 
     23         public static List
     
       ToList
      
       (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
       
         func = dataTable.Rows[0].ToExpression
        
         ();27             List
         
           collection = new List
          
           (dataTable.Rows.Count);28 foreach (DataRow dr in dataTable.Rows)29 {30 collection.Add(func(dr));31 }32 return collection;33 }34 35 36 /// 
           
37 /// 生成表达式38 /// 
39 /// 
           40 /// 
           41 /// 
           42 public static Func
           
             ToExpression
            
             (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
             
               binds = new List
              
               ();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
               
                
                 >(init, parameter).Compile();59 }60 #endregion61 /// 
                 
62 /// 生成lambda表达式63 /// 
64 /// 
                 65 /// 
                 66 /// 
                 67 public static Func
                 
                   ToExpression
                  
                   (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
                   
                     binds = new List
                    
                     ();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
                     
                      
                       >(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 Demo113 {14     class Program15     {16         static void Main(string[] args)17         {18             String conString = "Data Source=.; Initial Catalog=master; Integrated Security=true;";19             Func
     
       func = null;20             List
      
        usrs = new List
       
        ();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
        
         ();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 Usr51     {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

方案记录下来。

文中如果有不清楚或者有问题的地方请园友指出。谢谢。

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