Why this not work?

help
1

I try the next code work. What i doing wrong?.

use std::cell::RefCell;
use std::rc::Rc;

use sqlx::{Acquire, Error, MySql, Transaction};

type DBConn  = Rc<RefCell<sqlx::pool::PoolConnection<MySql>>>;
type DBTrans<'t> = Rc<RefCell<sqlx::Transaction<'t, MySql>>>;

// This work!!!. But is only the db connection
async fn connection_mysql<'c>(connection_pool: Option<&'c sqlx::Pool<sqlx::MySql>>) -> Result<DBConn, sqlx::Error> {
    match connection_pool {
        Some(connection_pool) => {

            let conn: sqlx::pool::PoolConnection<sqlx::MySql> = match connection_pool.acquire().await {
                Ok(conn) => conn,
                Err(error) => return Err(error),
            };

            let rc_conn: Rc<RefCell<sqlx::pool::PoolConnection<MySql>>> = Rc::new( RefCell::new( conn ) );

            Ok(rc_conn)

        }
        None => {
            Err(Error::PoolClosed)
        }
    }
}

//Not work. I Need the connection and the transaction
async fn begin_transaction_mysql<'c>(connection_pool: Option<&'c sqlx::Pool<sqlx::MySql>>) -> Result<(DBConn,DBTrans), sqlx::Error> {
    match connection_pool {
        Some(connection_pool) => {

            let conn: sqlx::pool::PoolConnection<sqlx::MySql> = match connection_pool.acquire().await {
                Ok(conn) => conn,
                Err(error) => return Err(error),
            };

            let rc_conn: Rc<RefCell<sqlx::pool::PoolConnection<MySql>>> = Rc::new( RefCell::new( conn ) );

            let mut trans = rc_conn.borrow_mut(); //I try with rc_conn.clone().borrow_mut(). Not work

            let rc_transaction: Rc<RefCell<Transaction<'_, MySql>>> = Rc::new( RefCell::new( trans.begin().await.unwrap()) );

            Ok(( rc_conn, rc_transaction)) //<-- Problem where

        }
        None => {
            Err(Error::PoolClosed)
        }
    }
}

The borrow checker has complaints. What i need to do for this work?

   Compiling sqlx_mysql_tokio_01 v0.1.0 (/home/dsystems01/Desktop/rust-lang/projects/test/sqlx_mysql_tokio_01)
error[E0515]: cannot return value referencing local variable `trans`
   --> src/main.rs:330:13
    |
328 |             let rc_transaction: Rc<RefCell<Transaction<'_, MySql>>> = Rc::new( RefCell::new( trans.begin().await.unwrap()) );
    |                                                                                              ----- `trans` is borrowed here
329 |
330 |             Ok(( rc_conn, rc_transaction))
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returns a value referencing data owned by the current function

error[E0515]: cannot return value referencing local variable `rc_conn`
   --> src/main.rs:330:13
    |
326 |             let mut trans = rc_conn.as_ref().borrow_mut(); //.into_inner();
    |                             ------- `rc_conn` is borrowed here
...
330 |             Ok(( rc_conn, rc_transaction))
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returns a value referencing data owned by the current function

error[E0505]: cannot move out of `rc_conn` because it is borrowed
   --> src/main.rs:330:18
    |
315 | async fn begin_transaction_mysql_01<'c>(connection_pool: Option<&'c sqlx::Pool<sqlx::MySql>>) -> Result<(DBConn,DBTrans), sqlx::Error> {
    |                                     -- lifetime `'c` defined here
...
324 |             let rc_conn: Rc<RefCell<sqlx::pool::PoolConnection<MySql>>> = Rc::new( RefCell::new( conn ) );
    |                 ------- binding `rc_conn` declared here
325 |
326 |             let mut trans = rc_conn.as_ref().borrow_mut(); //.into_inner();
    |                             ------- borrow of `rc_conn` occurs here
...
330 |             Ok(( rc_conn, rc_transaction))
    |             -----^^^^^^^------------------
    |             |    |
    |             |    move out of `rc_conn` occurs here
    |             returning this value requires that `rc_conn` is borrowed for `'c`

Some errors have detailed explanations: E0505, E0515.
For more information about an error, try `rustc --explain E0505`.

The message "returning this value requires that rc_conn is borrowed for 'c" what it mean?

Thanks for all help can get me.

2

Since both the connection and the transaction are behind the Rc smart pointer, you should simply return clones of them.

3

I changed the code but still get errors

//Not work. I Need the connection and the transaction
async fn begin_transaction_mysql<'c>(connection_pool: Option<&'c sqlx::Pool<sqlx::MySql>>) -> Result<(DBConn,DBTrans), sqlx::Error> {
    match connection_pool {
        Some(connection_pool) => {

            let conn: sqlx::pool::PoolConnection<sqlx::MySql> = match connection_pool.acquire().await {
                Ok(conn) => conn,
                Err(error) => return Err(error),
            };

            let rc_conn: Rc<RefCell<sqlx::pool::PoolConnection<MySql>>> = Rc::new( RefCell::new( conn ) );

            let rc_conn_cloned = rc_conn.clone();

            let rc_trans: Rc<RefCell<Transaction<'_, MySql>>> = Rc::new( RefCell::new( rc_conn_cloned.borrow_mut().begin().await.unwrap()) );

            let rc_trans_cloned = rc_trans.clone();

            Ok(( rc_conn, rc_trans_cloned))

        }
        None => {
            Err(Error::PoolClosed)
        }
    }
}

error[E0515]: cannot return value referencing temporary value
   --> src/main.rs:364:13
    |
360 |             let rc_trans: Rc<RefCell<Transaction<'_, MySql>>> = Rc::new( RefCell::new( rc_conn_cloned.borrow_mut().begin().await.unwrap()) );
    |                                                                                        --------------------------- temporary value created here
...
364 |             Ok(( rc_conn, rc_trans_cloned))
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returns a value referencing data owned by the current function

error[E0515]: cannot return value referencing local variable `rc_conn_cloned`
   --> src/main.rs:364:13
    |
360 |             let rc_trans: Rc<RefCell<Transaction<'_, MySql>>> = Rc::new( RefCell::new( rc_conn_cloned.borrow_mut().begin().await.unwrap()) );
    |                                                                                        -------------- `rc_conn_cloned` is borrowed here
...
364 |             Ok(( rc_conn, rc_trans_cloned))
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returns a value referencing data owned by the current function

For more information about this error, try `rustc --explain E0515`.
error: could not compile `sqlx_mysql_tokio_01` (bin "sqlx_mysql_tokio_01") due to 2 previous errors
4

You are almost there.

Change this:

Result<(DBConn,DBTrans)

To this:

Result<(Rc<RefCell<DBConn>>,Rc<RefCell<DBTrans>>)
5

Is already defined in top. I think not need nested Rc RefCell.

6

Transaction<'c> contains a reference to the Connection, and this creates a self-referential struct, which is not allowed to exist in Rust.

You will never be able to have Connection and Transaction<'connection> in the same struct or tuple. You must refactor the code to create and return Connection first, and then create Transaction separately.

2 Likes
7

Sorry, I had not seen that you already had this on the type aliases.

It seems that the only way to make it work would be to receive a connection as a parameter rather than a pool.

Besides that, I don't think you should be using a transaction like that. They are meant to be guards when performing different database operations, so you should only receive a mutable reference to a transaction to commit every operation.

8

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