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

using System;using System.Collections.Generic;using System.Data;using System.Data.Common;using System.Data.SqlClient;using System.Linq;using System.Linq.Expressions;using System.Reflection;using System.Text;using System.Threading.Tasks;namespace Demo1{ public static class EntityConverter { #region /// <summary> /// DataTable生成实体 /// </summary> /// <typeparam name="T"></typeparam> /// <param name="dataTable"></param> /// <returns></returns> public static List<T> ToList<T>(this DataTable dataTable) where T : class, new() { 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"); Func<DataRow, T> func = dataTable.Rows[0].ToExpression<T>(); List<T> collection = new List<T>(dataTable.Rows.Count); foreach (DataRow dr in dataTable.Rows) { collection.Add(func(dr)); } return collection; } /// <summary> /// 生成表达式 /// </summary> /// <typeparam name="T"></typeparam> /// <param name="dataRow"></param> /// <returns></returns> public static Func<DataRow, T> ToExpression<T>(this DataRow dataRow) where T : class, new() { if (dataRow == null) throw new ArgumentNullException("dataRow", "当前对象为null 无法转换成实体"); ParameterExpression parameter = Expression.Parameter(typeof(DataRow), "dr"); List<MemberBinding> binds = new List<MemberBinding>(); for (int i = 0; i < dataRow.ItemArray.Length; i++) { String colName = dataRow.Table.Columns[i].ColumnName; PropertyInfo pInfo = typeof(T).GetProperty(colName); if (pInfo == null || !pInfo.CanWrite) continue; MethodInfo mInfo = typeof(DataRowExtensions).GetMethod("Field", new Type[] { typeof(DataRow), typeof(String) }).MakeGenericMethod(pInfo.PropertyType); MethodCallExpression call = Expression.Call(mInfo, parameter, Expression.Constant(colName, typeof(String))); MemberAssignment bind = Expression.Bind(pInfo, call); binds.Add(bind); } MemberInitExpression init = Expression.MemberInit(Expression.New(typeof(T)), binds.ToArray()); return Expression.Lambda<Func<DataRow, T>>(init, parameter).Compile(); } #endregion /// <summary> /// 生成lambda表达式 /// </summary> /// <typeparam name="T"></typeparam> /// <param name="reader"></param> /// <returns></returns> public static Func<SqlDataReader, T> ToExpression<T>(this SqlDataReader reader) where T : class, new() { if (reader == null || reader.IsClosed || !reader.HasRows) throw new ArgumentException("reader", "当前对象无效"); ParameterExpression parameter = Expression.Parameter(typeof(SqlDataReader), "reader"); List<MemberBinding> binds = new List<MemberBinding>(); for (int i = 0; i < reader.FieldCount; i++) { String colName = reader.GetName(i); PropertyInfo pInfo = typeof(T).GetProperty(colName); if (pInfo == null || !pInfo.CanWrite) continue; MethodInfo mInfo = reader.GetType().GetMethod("GetFieldValue").MakeGenericMethod(pInfo.PropertyType); MethodCallExpression call = Expression.Call(parameter, mInfo, Expression.Constant(i)); MemberAssignment bind = Expression.Bind(pInfo, call); binds.Add(bind); } MemberInitExpression init = Expression.MemberInit(Expression.New(typeof(T)), binds.ToArray()); return Expression.Lambda<Func<SqlDataReader, T>>(init, parameter).Compile(); } }}

在上一篇的基础上增加了 SqlDataReader 的扩展方法

以下代码是调用

using System;using System.Collections.Generic;using System.Data;using System.Data.Common;using System.Data.SqlClient;using System.Diagnostics;using System.Linq;using System.Reflection;using System.Text;using System.Threading.Tasks;namespace Demo1{ class Program { static void Main(string[] args) { String conString = "Data Source=.; Initial Catalog=master; Integrated Security=true;"; Func<SqlDataReader, Usr> func = null; List<Usr> usrs = new List<Usr>(); using (SqlDataReader reader = GetReader(conString, "select object_id 'ID',name 'Name' from sys.objects", CommandType.Text, null)) { while (reader.Read()) { if (func == null) { func = reader.ToExpression<Usr>(); } Usr usr = func(reader); usrs.Add(usr); } } usrs.Clear(); Console.ReadKey(); } public static SqlDataReader GetReader(String conString, String sql, CommandType type, params SqlParameter[] pms) { SqlConnection conn = new SqlConnection(conString); SqlCommand cmd = new SqlCommand(sql, conn); cmd.CommandType = type; if (pms != null && pms.Count() > 0) { cmd.Parameters.AddRange(pms); } conn.Open(); return cmd.ExecuteReader(CommandBehavior.CloseConnection); } } class Usr { public Int32 ID { get; set; } public String Name { get; set; } }}

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。