Take advantage of borrowing for Database Object + Diesel

[insipx]

We deal exclusively with owned database objects like StoredGroup or StoredGroupMessage. We can instead borrow it directly from what the SQLite library returns from the database, avoiding unnecessary allocations. Furthermore, when inserting into the database we can use borrowed variants of our schema to avoid extra allocations before inserting.

There are an abundance of examples around the codebase, but load_identity_updates is a fairly well self-contained example:

/// For the given list of `inbox_id`s get all updates from the network that are newer than the last known `sequence_id`,
/// write them in the db, and return the updates
#[tracing::instrument(level = "trace", skip_all)]
pub async fn load_identity_updates<ApiClient: XmtpApi>(
    api_client: &ApiClientWrapper<ApiClient>,
    conn: &DbConnection,
    inbox_ids: &[&str],
) -> Result<HashMap<String, Vec<InboxUpdate>>, ClientError> {
    if inbox_ids.is_empty() {
        return Ok(HashMap::new());
    }
    tracing::debug!("Fetching identity updates for: {:?}", inbox_ids);

    let existing_sequence_ids = conn.get_latest_sequence_id(inbox_ids)?;
    let filters: Vec<GetIdentityUpdatesV2Filter> = inbox_ids
        .iter()
        .map(|inbox_id| GetIdentityUpdatesV2Filter {
            sequence_id: existing_sequence_ids.get(*inbox_id).map(|i| *i as u64),
            inbox_id: inbox_id.to_string(),
        })
        .collect();

    let updates = api_client.get_identity_updates_v2(filters).await?;

    let to_store = updates
        .iter()
        .flat_map(|(inbox_id, updates)| {
            updates.iter().map(|update| StoredIdentityUpdate {
                inbox_id: inbox_id.clone(),
                sequence_id: update.sequence_id as i64,
                server_timestamp_ns: update.server_timestamp_ns as i64,
                payload: update.update.clone().into(),
            })
        })
        .collect::<Vec<StoredIdentityUpdate>>();

    conn.insert_or_ignore_identity_updates(&to_store)?;
    Ok(updates)
}

we could instead insert a StoredIdentityUpdateRef<'_> that borrows inbox_id, and payload

For this one example it doesn't matter much, but multiplied over everywhere we load & store in the codebase, it could have a noticeable effect on perf.

[neekolas]

Love this idea