pub trait Acquire<'c> {
type Database: Database;
type Connection: Deref<Target = <Self::Database as Database>::Connection> + DerefMut + Send;
// Required methods
fn acquire(
self
) -> Pin<Box<dyn Future<Output = Result<Self::Connection, Error>> + Send + 'c, Global>>;
fn begin(
self
) -> Pin<Box<dyn Future<Output = Result<Transaction<'c, Self::Database>, Error>> + Send + 'c, Global>>;
}Expand description
Acquire connections or transactions from a database in a generic way.
If you want to accept generic database connections that implement
Acquire which then allows you to acquire a
connection or begin a transaction, then you can do it
like that:
async fn run_query<'a, A>(conn: A) -> Result<(), BoxDynError>
where
A: Acquire<'a, Database = Postgres>,
{
let mut conn = conn.acquire().await?;
sqlx::query!("SELECT 1 as v").fetch_one(&mut *conn).await?;
sqlx::query!("SELECT 2 as v").fetch_one(&mut *conn).await?;
Ok(())
}If you run into a lifetime error about “implementation of sqlx::Acquire is
not general enough”, the workaround looks like this:
fn run_query<'a, 'c, A>(conn: A) -> impl Future<Output = Result<(), BoxDynError>> + Send + 'a
where
A: Acquire<'c, Database = Postgres> + Send + 'a,
{
async move {
let mut conn = conn.acquire().await?;
sqlx::query!("SELECT 1 as v").fetch_one(&mut *conn).await?;
sqlx::query!("SELECT 2 as v").fetch_one(&mut *conn).await?;
Ok(())
}
}However, if you really just want to accept both, a transaction or a connection as an argument to a function, then it’s easier to just accept a mutable reference to a database connection like so:
async fn run_query(conn: &mut PgConnection) -> Result<(), BoxDynError> {
sqlx::query!("SELECT 1 as v").fetch_one(&mut *conn).await?;
sqlx::query!("SELECT 2 as v").fetch_one(&mut *conn).await?;
Ok(())
}The downside of this approach is that you have to acquire a connection
from a pool first and can’t directly pass the pool as argument.