rust - 将 Diesel 连接注入(inject) Iron 中间件

Question

在编写我的测试时，我希望能够在请求中注入(inject)一个连接，这样我就可以将整个测试用例包装在一个事务中(即使测试用例中有多个请求)。

我尝试使用 BeforeMiddleware 来做到这一点，我可以在我的测试用例中链接它以插入连接，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，我在尝试执行此操作时遇到编译错误:

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`

有没有办法通过柴油机连接解决这个问题？我在 Github 上找到了几个使用 pg crate 执行此操作的示例，但我想继续使用 diesel。

Answer 1

This answer肯定会解决问题，但这不是最佳选择。如前所述，您不能共享单个连接，因为它不是线程安全的。然而，虽然将其包装在 Mutex 中使其成为线程安全的，但它会强制所有服务器线程使用单个 连接。相反，您想使用连接池。

您可以使用 r2d2 来完成此操作和 r2d2-diesel crate 。这将根据需要建立多个连接，并在可能的情况下以线程安全的方式重用它们。