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

 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 <= ) throw new ArgumentNullException("dataTable", "当前对象为null无法生成表达式树");
             Func<DataRow, T> func = dataTable.Rows[].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 = ; 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 = ; 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() > )
             {
                 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。

文中如果有不清楚或者有问题的地方请园友指出。谢谢。

原创作品，转载请注明出处：http://www.cnblogs.com/lclblog/p/6711292.html