Struct db_dump::Index

source ·

pub struct Index<'a> { /* private fields */ }

Expand description

Lazy index of those tables that have a unique ID column as primary key.

Example

This example prints the top 5 most downloaded crates in each of the top 20 most popular categories.

use db_dump::categories::CategoryId;
use db_dump::crates::CrateId;
use db_dump::DbDump;
use std::cmp::Reverse;
use std::collections::BTreeMap as Map;

fn main() -> db_dump::Result<()> {
    let mut db = DbDump::default();
    let ref mut crates = db.crates;
    let mut categories = Vec::new();
    let mut crates_by_category = Map::<CategoryId, Vec<CrateId>>::new();
    db_dump::Loader::new()
        .crates(|row| crates.push(row))
        .categories(|row| categories.push(row))
        .crates_categories(|row| {
            crates_by_category
                .entry(row.category_id)
                .or_default()
                .push(row.crate_id)
        })
        .load("./db-dump.tar.gz")?;

    // Lazy index to perform lookups by crate id.
    let index = db.index();

    // Sort categories descending by number of crates, to print most popular
    // categories first.
    categories.sort_unstable_by_key(|category| Reverse(category.crates_cnt));

    for category in categories.iter().take(20) {
        // Get the list of crates in this category.
        let mut crates = crates_by_category.remove(&category.id).unwrap_or_default();

        // Sort crates list by download count descending.
        crates.sort_unstable_by_key(|&id| Reverse(index.krate(id).downloads));

        // Print top 5 most downloaded crates in category.
        print!("{}", category.slug);
        for crate_id in crates.into_iter().take(5) {
            print!(",{}", index.krate(crate_id).name);
        }
        println!();
    }

    Ok(())
}