There is already an open DataReader associated with this Connection which must be closed first

最近在写WebApi接口，遇到一些问题，总结一下。这些问题未必跟WebApi有关系，比较琐碎。

总结列表：
1. There is already an open DataReader associated with this Connection which must be closed first
2. npm install 失败
3. WebApi HTTP Put 405 Method not allowed

问题现象：一个接口被多次调用，可以认为是多线程调用接口，接口内部使用了C#的Async Await，代码形如:

return new GetXResponse
{
A= await A.GetAAsync(xx),
B= await B.GetBAsync(xx),
C= await C.GetCAsync(xx),
D= await D.GetDAsync(xx),
E= await E.GetEAsync(xx),
F= await F.GetFAsync(xx),
G= await G.GetGAsync(xx)
};
犯了一个错误，A、B、C、D等等都会连接数据库，连接数据库的代码，使用using不当
using (Connection)
{
return (await conn.QueryAsync<T>(sql, parms)).ToList();
}

Connection是在构造函数完成的初始化 new MySqlConnection，多线程调用时，using未及时回收数据库连接，修改如下之后，该异常可修复。

using (var conn = new MySqlConnection(ConnString))
{
return (await conn.QueryAsync<T>(sql, parms)).ToList();
}