|
这篇文章主要介绍了SqlDataReader生成动态Lambda表达式,需要的朋友可以参考下
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。 | 
发表于 2017-4-23 09:27:29
