example.rs

// What I write right now

pub fn all(conn: &Conn) -> Result<Vec<FullStoredRepo>> {
    use schema::repos::dsl::*;
    let rs: Vec<StoredRepo> = repos.load(conn).with_context(|| "getting all repos")?;

    let ids: Vec<i32> = rs.iter().map(|r| r.id).collect();

    use schema::issues::dsl::{issues, repo_id as issue_repo_id};
    let isx = issues
        .filter(issue_repo_id.eq_any(ids.clone()))
        .load::<StoredIssue>(conn)?
        .grouped_by(&rs[..]);

    use schema::pull_requests::dsl::{pull_requests, repo_id as pr_repo_id};
    let prs = pull_requests
        .filter(pr_repo_id.eq_any(ids.clone()))
        .load::<StoredPullRequest>(conn)?
        .grouped_by(&rs[..]);

    use schema::repo_activity_log::dsl::{repo_activity_log, repo_id as activity_repo_id};
    let activities = repo_activity_log
        .filter(activity_repo_id.eq_any(ids.clone()))
        .load::<StoredRepoEvent>(conn)?
        .grouped_by(&rs[..]);

    Result::Ok(
        rs.into_iter()
            .zip(isx)
            .zip(prs)
            .zip(activities)
            .map(|(((repo, issue), prs), events)| FullStoredRepo {
                id: repo.id,
                title: repo.title.clone(),
                issues: issue,
                prs,
                events,
            })
            .collect(),
    )
}

// What I would like to write
pub fn all(conn: &Conn) -> Result<Vec<FullStoredRepo>> {
    use schema::repos::dsl::{repos, id as repo_id};
    let rs: Vec<StoredRepo> = repos.load(conn).with_context(|| "getting all repos")?;

    let ids: Vec<i32> = rs.iter().map(|r| r.id).collect();

    use schema::issues::dsl::issues;
    let isx = issues
        .filter(repo_id.eq_any(ids.clone())) // NOTE: repo_id is a use-alias to the id of the repo table 
        .load::<StoredIssue>(conn)?
        .grouped_by(&rs[..]);

    use schema::pull_requests::dsl::pull_requests;
    let prs = pull_requests
        .filter(repo_id.eq_any(ids.clone()))  // NOTE: same
        .load::<StoredPullRequest>(conn)?
        .grouped_by(&rs[..]);

    use schema::repo_activity_log::dsl::repo_activity_log;
    let activities = repo_activity_log
        .filter(repo_id.eq_any(ids.clone()))  // NOTE: same
        .load::<StoredRepoEvent>(conn)?
        .grouped_by(&rs[..]);

    Result::Ok(
        rs.into_iter()
            .zip(isx)
            .zip(prs)
            .zip(activities)
            .map(|(((repo, issue), prs), events)| FullStoredRepo {
                id: repo.id,
                title: repo.title.clone(),
                issues: issue,
                prs,
                events,
            })
            .collect(),
    )
}