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
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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
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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。
原文链接:http://www.cnblogs.com/lclblog/p/6711292.html