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 == )
                 return list;
             DataTableEntityBuilder<T> eblist = DataTableEntityBuilder<T>.CreateBuilder(dt.Rows[]);
             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 = ; 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。