如何将DataReader结果转换为实体？ -> 使用发出
现在我想将 DataReader 转换为 Entity 。我有一个这样的方法：
private static void ReadInt32(ILGenerator il, LocalBuilder item,
List<DbColumnInfo> columnInfoes, LocalBuilder[] colIndices, int i)
{
il.Emit(OpCodes.Ldloc_S, item);
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldloc_S, colIndices[i]);
il.Emit(OpCodes.Callvirt, DataRecord_GetInt32);
il.Emit(OpCodes.Callvirt, columnInfoes[i].SetMethod);
}
并像这里一样调用该方法，
if (IsCompatibleType(columnInfoes[i].Type, typeof(int)))
{
// item.%Property% = arg.GetInt32(%index%);
ReadInt32(il, item, columnInfoes, colIndices, i);
}
不幸的是，如果数据库中的数据归档为空，则会出现异常。由于 int 类型不能为 NULL 值，但我将其转换为 int?。然后事实证明我的调用方法效果很好。
但这里我想要一个扩展，即当数据库中的数据归档为NULL时，我们可以使用自定义属性来指示默认值。所以我重新定义了ReadInt32如下，但令我惊讶的是，总是出现JIT内部异常。我对IL不熟悉，我真的很希望能为大家提供一些帮助，非常感谢。
将代码更改如下，但仍然存在错误，异常类型是： System.EntryPointNotFoundException：
var local = il.DeclareLocal(columnInfoes[i].Type);//int i
Label intNull = il.DefineLabel();//int intNull;
Label intCommon = il.DefineLabel();
il.Emit(OpCodes.Ldloca, local);
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldloc_S, colIndices[i]);
il.Emit(OpCodes.Callvirt, DataRecord_IsDBNull);// int i=isdbnull?
il.Emit(OpCodes.Brtrue_S, intNull);// int i=isdbnull?intNull
il.Emit(OpCodes.Ldloc_0);
il.Emit(OpCodes.Ldloc_S, colIndices[i]);//int i=isdbnull?1000:getInt(32)
il.Emit(OpCodes.Callvirt, DataRecord_GetInt32);//int i=isdbnull?1000:getInt32(i);
il.Emit(OpCodes.Br_S, intCommon);
il.MarkLabel(intNull);;
il.Emit(OpCodes.Ldc_I4, 123);//intNull=DefaultValue columnInfoes[i].DefaultValue
il.MarkLabel(intCommon);
il.Emit(OpCodes.Stloc_S, item);
//il.Emit(OpCodes.Ldloc_S, item);
il.Emit(OpCodes.Ldloc, local);
il.Emit(OpCodes.Callvirt, columnInfoes[i].SetMethod);
Now I want to Convert a DataReader to an Entity . I have a method like this:
private static void ReadInt32(ILGenerator il, LocalBuilder item,
List<DbColumnInfo> columnInfoes, LocalBuilder[] colIndices, int i)
{
il.Emit(OpCodes.Ldloc_S, item);
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldloc_S, colIndices[i]);
il.Emit(OpCodes.Callvirt, DataRecord_GetInt32);
il.Emit(OpCodes.Callvirt, columnInfoes[i].SetMethod);
}
and call the method like here,
if (IsCompatibleType(columnInfoes[i].Type, typeof(int)))
{
// item.%Property% = arg.GetInt32(%index%);
ReadInt32(il, item, columnInfoes, colIndices, i);
}
unfortunately, there will come up an Exception if the Data Filed in DB is NULL. As int type can't be NULL value but I made it transfer to int?. then turns out that my calling method works well.
but here I want an extension that is while Data Filed in DB is NULL, we can use Custom attribute to indicate a default value. So I re-defined ReadInt32 as following, But to my surprise, there always comming up JIT inner Exception. I'm not familiar with IL, I really looking forward some help for you all, really appreciate.
change the code's as following,but still exist error,the exception type is :
System.EntryPointNotFoundException:
var local = il.DeclareLocal(columnInfoes[i].Type);//int i
Label intNull = il.DefineLabel();//int intNull;
Label intCommon = il.DefineLabel();
il.Emit(OpCodes.Ldloca, local);
il.Emit(OpCodes.Ldarg_0);
il.Emit(OpCodes.Ldloc_S, colIndices[i]);
il.Emit(OpCodes.Callvirt, DataRecord_IsDBNull);// int i=isdbnull?
il.Emit(OpCodes.Brtrue_S, intNull);// int i=isdbnull?intNull
il.Emit(OpCodes.Ldloc_0);
il.Emit(OpCodes.Ldloc_S, colIndices[i]);//int i=isdbnull?1000:getInt(32)
il.Emit(OpCodes.Callvirt, DataRecord_GetInt32);//int i=isdbnull?1000:getInt32(i);
il.Emit(OpCodes.Br_S, intCommon);
il.MarkLabel(intNull);;
il.Emit(OpCodes.Ldc_I4, 123);//intNull=DefaultValue columnInfoes[i].DefaultValue
il.MarkLabel(intCommon);
il.Emit(OpCodes.Stloc_S, item);
//il.Emit(OpCodes.Ldloc_S, item);
il.Emit(OpCodes.Ldloc, local);
il.Emit(OpCodes.Callvirt, columnInfoes[i].SetMethod);
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（1）
只需使用 Dapper。如果这对 SO 有好处，那对你也有好处;-)
Just use Dapper. If it's good for SO, it will be good for you, too ;-)