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 <= 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();  } }}