codd

codd is a library for evaluating typed relational expressions in a monotonically growing minimal database in memory. codd is primarily developed to support an implementation of razor based on relational algebra, however, its design is consistent with common concepts of database theory and may be used as a minimal general purpose database.

The implementation of database instances in codd is borrowed from datafrog:

• Instance<T> (Variable<T> in datafrog) contains tuples of type T,
• Incremental view maintenance is implemented by maintaining tuples of Instance<T> in three sets of to_add (candidate tuples to be inserted), recent (recently added tuples), and stable (old tuples that have been reflected in all views).

In contrast, codd distinguishes relation instances from views and offers the trait Expression<T> and types that implement Expression<T> to query a database.

The relational algebra and database terminology in codd is adopted from Alice's book.

Build

codd is written in Rust. You can use Rust 1.54.0 or newer to build the library:

git clone https://github.com/salmans/codd.git
cd codd
cargo build

Example: music

Add codd to your project dependencies in Cargo.toml:

[dependencies]
codd = "0.1"

Use codd in your code:

use codd::{Database, Error, Expression};

Create a new database:

    let mut music = Database::new(); // music database

Add relations to the database:

    // `musician`, `band` and `song` are `Relation` expressions.
    let musician = music.add_relation("musician")?;
    let band = music.add_relation("band")?;
    let song = music.add_relation("song")?;

Insert tuples (records) to your database relations:

    music.insert(
        &musician,
        vec![
            Musician {
                name: "John Petrucci".into(),
                band: Some("Dream Theater".into()),
                instruments: vec![Guitar],
            },
            Musician {
                name: "Taylor Swift".into(),
                band: None,
                instruments: vec![Vocals],
            },
            // more tuples...
        ]
        .into(),
    )?;
    
    // add tuples to other relations...

Construct query expressions and evaluate them in the database:

    let guitarist_name = musician
        .builder()
        .select(|m| m.instruments.contains(&Guitar))
        .project(|g| g.name.to_string())
        .build();

    assert_eq!(
        vec![
            "Alex Turner".to_string(),
            "Conor Mason".into(),
            "John Petrucci".into(),
        ],
        music.evaluate(&guitarist_name)?.into_tuples() // evaluate the query and get the results
    );

Here is a more complex query:

    let dt_member = musician
        .builder()
        .with_key(|m| m.band.clone())
            // use `band` as the join key for `musician`
        .join(band.builder().with_key(|b| Some(b.name.clone()))) 
            // join with `band` with `name` as the join key
        .on(|_, m, b| (m.name.to_string(), b.name.to_string()))
            // combine tuples of `musician` and `band` in a new relation
        .select(|m| m.1 == "Dream Theater")
        .project(|m| m.0.to_string())
        .build();

    assert_eq!(
        vec!["John Petrucci".to_string(), "Jordan Rudess".into()],
        music.evaluate(&dt_member)?.into_tuples()
    );

Store views of expressions:

    let dt_member_view = music.store_view(dt_members)?; // view on `dt_member`
    let drummer_view = music.store_view(                // drummers view
        musician
            .builder()
            .select(|m| m.instruments.contains(&Drums))
            .build(),
    )?;

    // inserting more tuples:
    music.insert(
        &musician,
        vec![
            Musician {
                name: "John Myung".into(),
                band: Some("Dream Theater".into()),
                instruments: vec![Guitar],
            },
            Musician {
                name: "Mike Mangini".into(),
                band: Some("Dream Theater".into()),
                instruments: vec![Drums],
            },
        ]
        .into(),
    )?;

    // views are up-to-date:
    assert_eq!(
        vec![
            Musician {
                name: "Lars Ulrich".into(),
                band: Some("Metallica".into()),
                instruments: vec![Drums]
            },
            Musician {
                name: "Mike Mangini".into(),
                band: Some("Dream Theater".into()),
                instruments: vec![Drums]
            }
        ],
        music.evaluate(&drummer_view)?.into_tuples()
    );
    assert_eq!(
        vec![
            "John Myung".to_string(),
            "John Petrucci".into(),
            "Jordan Rudess".into(),
            "Mike Mangini".into()
        ],
        music.evaluate(&dt_member_view)?.into_tuples()
    );

    Ok(())
}