向铁中间件中注入柴油连接

Question

在编写测试时，我希望能够向请求中注入一个连接，以便能够将整个测试用例封装在一个事务中(即使测试用例中有多个请求)。

我尝试使用BeforeMiddleware来实现这一点，我可以将其链接到测试用例中来插入连接，如下所示：

pub type DatabaseConnection = PooledConnection<ConnectionManager<PgConnection>>;

pub struct DatabaseOverride {
    conn: DatabaseConnection,
}

impl BeforeMiddleware for DatabaseOverride {
    fn before(&self, req: &mut Request) -> IronResult<()> {
        req.extensions_mut().entry::<DatabaseOverride>().or_insert(self.conn);
        Ok(())
    }
}

但是，我在尝试这样做时遇到了一个编译错误：

error: the trait bound `std::rc::Rc<diesel::pg::connection::raw::RawConnection>: std::marker::Sync` is not satisfied [E0277]
impl BeforeMiddleware for DatabaseOverride {
     ^~~~~~~~~~~~~~~~
help: run `rustc --explain E0277` to see a detailed explanation
note: `std::rc::Rc<diesel::pg::connection::raw::RawConnection>` cannot be shared between threads safely
note: required because it appears within the type `diesel::pg::PgConnection`
note: required because it appears within the type `r2d2::Conn<diesel::pg::PgConnection>`
note: required because it appears within the type `std::option::Option<r2d2::Conn<diesel::pg::PgConnection>>`
note: required because it appears within the type `r2d2::PooledConnection<r2d2_diesel::ConnectionManager<diesel::pg::PgConnection>>`
note: required because it appears within the type `utility::db::DatabaseOverride`
note: required by `iron::BeforeMiddleware`

error: the trait bound `std::cell::Cell<i32>: std::marker::Sync` is not satisfied [E0277]
impl BeforeMiddleware for DatabaseOverride {
     ^~~~~~~~~~~~~~~~
help: run `rustc --explain E0277` to see a detailed explanation
note: `std::cell::Cell<i32>` cannot be shared between threads safely
note: required because it appears within the type `diesel::pg::PgConnection`
note: required because it appears within the type `r2d2::Conn<diesel::pg::PgConnection>`
note: required because it appears within the type `std::option::Option<r2d2::Conn<diesel::pg::PgConnection>>`
note: required because it appears within the type `r2d2::PooledConnection<r2d2_diesel::ConnectionManager<diesel::pg::PgConnection>>`
note: required because it appears within the type `utility::db::DatabaseOverride`
note: required by `iron::BeforeMiddleware`

有什么办法可以绕过柴油的连接吗？我已经找到了几个使用pg机箱来完成这个任务的例子，但是我还是想继续使用柴油。

Answer 1

这个答案当然会解决这个问题，但它不是最优的。如前所述，您不能共享一个连接，因为它不是线程安全的。但是，在将其封装在Mutex中使其线程安全的同时，它将强制所有服务器线程使用单个连接。相反，您希望使用连接池。

您可以使用r2d2和R2D2-柴油板条箱来完成这一任务。这将根据需要建立多个连接，并在可能时以线程安全的方式重用它们。