大数据量下DataTable To List效率对比

使用反射和动态生成代码两种方式（Reflect和Emit）

反射将DataTable转为List方法

public static List<T> ToListByReflect<T>(this DataTable dt) where T : new()
{
    List<T> ts = new List<T>();
    string tempName = string.Empty;
    T t = new T();
    PropertyInfo[] propertys = t.GetType().GetProperties();
    foreach (DataRow dr in dt.Rows)
    {
        foreach (PropertyInfo pi in propertys)
        {
            tempName = pi.Name;
            if (dt.Columns.Contains(tempName))
            {
                object value = dr[tempName];
                if (value != DBNull.Value)
                {
                    pi.SetValue(t, value, null);
                }
            }
        }
        ts.Add(t);
    }
    return ts;
}

动态生成代码将DataTable转为List方法

public static List<T> ToListByEmit<T>(this DataTable dt) where T : class, new()
        {
            List<T> list = new List<T>();
            if (dt == null || dt.Rows.Count == 0)
                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<Entity>
        {
            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 Entity Load(DataRow dataRecord);
            private Load handler;
            private DataTableEntityBuilder() { }
            public Entity Build(DataRow dataRecord)
            {
                return handler(dataRecord);
            }
            public static DataTableEntityBuilder<Entity> CreateBuilder(DataRow dataRecord)
            {
                DataTableEntityBuilder<Entity> dynamicBuilder = new DataTableEntityBuilder<Entity>();
                DynamicMethod method = new DynamicMethod("DynamicCreateEntity", typeof(Entity), new Type[] { typeof(DataRow) }, typeof(Entity), true);
                ILGenerator generator = method.GetILGenerator();
                LocalBuilder result = generator.DeclareLocal(typeof(Entity));
                generator.Emit(OpCodes.Newobj, typeof(Entity).GetConstructor(Type.EmptyTypes));
                generator.Emit(OpCodes.Stloc, result);
                for (int i = 0; i < dataRecord.ItemArray.Length; i++)
                {
                    PropertyInfo propertyInfo = typeof(Entity).GetProperty(dataRecord.Table.Columns[i].ColumnName);
                    Label endIfLabel = generator.DefineLabel();
                    if (propertyInfo != null && propertyInfo.GetSetMethod() != null)
                    {
                        generator.Emit(OpCodes.Ldarg_0);
                        generator.Emit(OpCodes.Ldc_I4, i);
                        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, i);
                        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;
            }
        }

然后写个控制台程序，对比一下两个方法的效率（测试类大概有40个属性）

电脑比较渣，使用Emit方法转换100w条数据大概需要7秒，而反射则需要37秒。还测试了当数据量比较小时，Reflect反而比较快。