DataTableToList 优化后

最新推荐文章于 2023-04-16 10:46:36 发布

转载最新推荐文章于 2023-04-16 10:46:36 发布 · 59 阅读

本文介绍了一种使用Emit技术将DataTable快速转换为实体列表的方法，针对大量数据处理进行了优化，显著提高了转换效率。

View Code http://www.codeproject.com/Articles/19513/Dynamic-But-Fast-The-Tale-of-Three-Monkeys-A-Wolf

using System;
using System.Collections.Generic;
using System.Data;
using System.Reflection;
using System.Reflection.Emit;
using System.Text;
using System.Threading.Tasks;

namespace SharpShell
{
    //DataTable转Entity(Emit版)
    //30000条数据,直接发射的话7秒多,Emit1.2秒左右
    public static class NewClas
    {

        public static List<T> ToList<T>(DataTable dt)
        {
            List<T> list = new List<T>();
            if (dt == null) return list;
            DataTableEntityBuilder<T> eblist = DataTableEntityBuilder<T>.CreateBuilder(dt.Rows[0]);
            foreach (DataRow info in dt.Rows)
                list.Add(eblist.Build(info));
            dt.Dispose();
            dt = null;
            return list;
        }

        public class DataTableEntityBuilder<T>
        {
            private static readonly MethodInfo getValueMethod = typeof (DataRow).GetMethod("get_Item",
                                                                                           new Type[] {typeof (int)});

            private static readonly MethodInfo isDBNullMethod = typeof (DataRow).GetMethod("IsNull",
                                                                                           new Type[] {typeof (int)});

            private delegate T Load(DataRow dataRecord);

            private Load handler;

            private DataTableEntityBuilder()
            {
            }

            public T Build(DataRow dataRecord)
            {
                return handler(dataRecord);
            }


            public static DataTableEntityBuilder<T> CreateBuilder(DataRow dataRow)
            {
                DataTableEntityBuilder<T> dynamicBuilder = new DataTableEntityBuilder<T>();
                DynamicMethod method = new DynamicMethod("DynamicCreateEntity", typeof (T),
                                                         new Type[] {typeof (DataRow)}, typeof (T), true);
                ILGenerator generator = method.GetILGenerator();
                LocalBuilder result = generator.DeclareLocal(typeof (T));
                generator.Emit(OpCodes.Newobj, typeof (T).GetConstructor(Type.EmptyTypes));
                generator.Emit(OpCodes.Stloc, result);

                for (int index = 0; index < dataRow.ItemArray.Length; index++)
                {
                    PropertyInfo propertyInfo = typeof (T).GetProperty(dataRow.Table.Columns[index].ColumnName);
                    Label endIfLabel = generator.DefineLabel();
                    if (propertyInfo != null && propertyInfo.GetSetMethod() != null)
                    {
                        generator.Emit(OpCodes.Ldarg_0);
                        generator.Emit(OpCodes.Ldc_I4, index);
                        generator.Emit(OpCodes.Callvirt, isDBNullMethod);
                        generator.Emit(OpCodes.Brtrue, endIfLabel);
                        generator.Emit(OpCodes.Ldloc, result);
                        generator.Emit(OpCodes.Ldarg_0);
                        generator.Emit(OpCodes.Ldc_I4, index);
                        generator.Emit(OpCodes.Callvirt, getValueMethod);
                        generator.Emit(OpCodes.Unbox_Any, propertyInfo.PropertyType);
                        generator.Emit(OpCodes.Callvirt, propertyInfo.GetSetMethod());
                        generator.MarkLabel(endIfLabel);
                    }
                }
                generator.Emit(OpCodes.Ldloc, result);
                generator.Emit(OpCodes.Ret);
                dynamicBuilder.handler = (Load) method.CreateDelegate(typeof (Load));
                return dynamicBuilder;
            }
        }
    }
}