I have to use two Connection guard. Can I use only one Connection guard

[paulzhang5511]

#[derive(Database)]
#[database("demo")]
pub struct Db(sqlx::MySqlPool);

/// whether the user already exists by mobile phone number 
pub async fn exist_by_mobile(mut db: Connection<Db>, phone_num: &String) -> Result<bool, sqlx::Error> {
  ...
}

// save user
pub async fn insert(mut db: Connection<Db>, user: &UserCreate) -> anyhow::Result<u64> {
  ...
}


#[post("/register", data = "<user>")]
pub async fn register_handle(mut db1: Connection<Db>, mut db2: Connection<Db>, user: Json<UserCreate>) -> Json<WebData<HashMap<String,String>>> {
    exist_by_mobile(db1, &user.mobile).await;
  
    ...

    insert(db2, &user) .await
    ...
}

I have to use two Connection guard. Can I use only one Connection guard.

[the10thWiz]

I believe you can use either &Connection<Db> or &mut Connection<Db> in both exist_by_mobile and insert, which will allow you to reuse the same connection for both.

[paulzhang5511]

pub async fn find_by_mobile(
    mut db: Connection<Db>,
    mobile: &String,
) -> anyhow::Result<UserVerifyPassword> {
    let user: UserVerifyPassword = sqlx::query_as!(
        UserVerifyPassword,
        r#"
        SELECT id, mobile, password, role
        FROM users
        WHERE mobile=?
       "#,
        mobile,
    )
    .fetch_one(&mut *db)
    .await?;
    Ok(user)
}

The fetch_one must be mut. If the function is modified as follows.

pub async fn exist_by_mobile(db: &Connection<Db>, mobile: &String) -> Result<bool, sqlx::Error> {
    let query_count: QueryCount = sqlx::query_as!(
        QueryCount,
        r#"
            SELECT COUNT(*) as count FROM users WHERE mobile = ?
        "#,
        mobile
    )
    .fetch_one(&*db)
    .await?;
    Ok(query_count.count > 0)
}

[bubelov]

@paulzhang5511

Try changing

pub async fn exist_by_mobile(db: &Connection<Db>, mobile: &String)

to

pub async fn exist_by_mobile(db: &mut Connection<Db>, mobile: &String)

Also, this line looks odd:

.fetch_one(&*db)

You can probably replace it with:

.fetch_one(db)

The idea is to prevent ownership transfer by passing the database as a reference, but this reference should also be mutable

[paulzhang5511]

@bubelov bubelov

.fetch_one(db)

To

.fetch_one(&mut **db)

Is it right?

[bubelov]

@paulzhang5511 possible, check the docs and compiler output, they should be able to guide you further. Just don't pass your DB connection directly when calling nested functions, it should allow you to call them more than once