Rust: Streams should borrow the transaction

[dmitrii-ubskii]

Problem to Solve

Currently it is possible to write this:

fn get_users(database: Database) -> Result<impl Stream<Item = Result<ConceptMap>>> {
    Session::new(database, Data).await?
        .transaction(TransactionType::Read).await?
        .query().match_("match $x isa user;")
}

This compiles and correctly returns the match query stream. However, as soon as we exit the scope of the function, the transaction is dropped and closed, and the stream is closed immediately, returning no items. This behaviour is confusing.

Proposed Solution

Query and concept streams should be bound by the lifetime of the transaction (/ query manager / concept manager). In that case, the above snippet will not compile, forcing the user to either hold on to the session and transaction handles, or retrieve all the data up front.