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use crate::{
error::Error,
prelude::{Heading, Relation, Tuple},
};
impl Relation {
/// Performs a natural join on attributes shared by both relations (`⋈`).
///
/// `users`
///
/// | `id` | `score` |
/// | --- | --- |
/// | `1` | `10` |
/// | `2` | `20` |
///
/// `cities`
///
/// | `id` | `level` |
/// | --- | --- |
/// | `1` | `100` |
/// | `3` | `300` |
///
/// Output
///
/// | `id` | `score` | `level` |
/// | --- | --- | --- |
/// | `1` | `10` | `100` |
///
/// # Errors
///
/// Returns [`Error::ScalarTypeMismatch`] if shared attribute names exist in
/// both relations with different scalar types.
///
/// # Example
///
/// ```rust
/// use darwen::prelude::{AttributeName, Heading, Relation, Scalar, ScalarType, Tuple};
///
/// let users = Relation::new_from_iter(
/// Heading::try_from(vec![
/// (AttributeName::from("id"), ScalarType::Integer),
/// (AttributeName::from("score"), ScalarType::Integer),
/// ])?,
/// vec![
/// Tuple::try_from(vec![
/// (AttributeName::from("id"), Scalar::Integer(1)),
/// (AttributeName::from("score"), Scalar::Integer(10)),
/// ])?,
/// Tuple::try_from(vec![
/// (AttributeName::from("id"), Scalar::Integer(2)),
/// (AttributeName::from("score"), Scalar::Integer(20)),
/// ])?,
/// ],
/// )?;
/// let cities = Relation::new_from_iter(
/// Heading::try_from(vec![
/// (AttributeName::from("id"), ScalarType::Integer),
/// (AttributeName::from("level"), ScalarType::Integer),
/// ])?,
/// vec![
/// Tuple::try_from(vec![
/// (AttributeName::from("id"), Scalar::Integer(1)),
/// (AttributeName::from("level"), Scalar::Integer(100)),
/// ])?,
/// Tuple::try_from(vec![
/// (AttributeName::from("id"), Scalar::Integer(3)),
/// (AttributeName::from("level"), Scalar::Integer(300)),
/// ])?,
/// ],
/// )?;
///
/// let users_with_levels = users.join(&cities)?;
///
/// assert_eq!(
/// users_with_levels,
/// Relation::new_from_iter(
/// Heading::try_from(vec![
/// (AttributeName::from("id"), ScalarType::Integer),
/// (AttributeName::from("score"), ScalarType::Integer),
/// (AttributeName::from("level"), ScalarType::Integer),
/// ])?,
/// vec![Tuple::try_from(vec![
/// (AttributeName::from("id"), Scalar::Integer(1)),
/// (AttributeName::from("score"), Scalar::Integer(10)),
/// (AttributeName::from("level"), Scalar::Integer(100)),
/// ])?],
/// )?
/// );
/// # Ok::<(), darwen::prelude::Error>(())
/// ```
pub fn join(&self, other: &Relation) -> Result<Relation, Error> {
let common = self.heading.common(&other.heading)?;
if common.is_empty() {
// TODO: error?
return self.product(other);
}
let mut attributes = self.heading.attributes.clone();
for (name, ty) in other.heading.iter() {
if !attributes.contains_key(name) {
attributes.insert(name.clone(), *ty);
}
}
let mut result = Relation::new(Heading::new(attributes));
for lhs in &self.body {
for rhs in &other.body {
if !common.iter().all(|name| lhs.get(name) == rhs.get(name)) {
continue;
}
let mut values = lhs.values.clone();
for (name, value) in rhs.iter() {
if !values.contains_key(name) {
values.insert(name.clone(), value.clone());
}
}
result.insert(Tuple::from(values))?;
}
}
Ok(result)
}
}
#[cfg(test)]
mod tests {
use crate::{
prelude::{Heading, Scalar, ScalarType, Tuple},
types::AttributeName,
};
use super::*;
#[test]
fn test_join() {
let relation = Relation::new_from_iter(
Heading::try_from(vec![
(AttributeName::from("a"), ScalarType::Boolean),
(AttributeName::from("b"), ScalarType::Integer),
])
.unwrap(),
vec![
Tuple::try_from(vec![
(AttributeName::from("a"), Scalar::Boolean(true)),
(AttributeName::from("b"), Scalar::Integer(1)),
])
.unwrap(),
Tuple::try_from(vec![
(AttributeName::from("a"), Scalar::Boolean(true)),
(AttributeName::from("b"), Scalar::Integer(2)),
])
.unwrap(),
Tuple::try_from(vec![
(AttributeName::from("a"), Scalar::Boolean(true)),
(AttributeName::from("b"), Scalar::Integer(3)),
])
.unwrap(),
],
)
.unwrap();
let other = Relation::new_from_iter(
Heading::try_from(vec![
(AttributeName::from("b"), ScalarType::Integer),
(AttributeName::from("c"), ScalarType::Integer),
])
.unwrap(),
vec![
Tuple::try_from(vec![
(AttributeName::from("b"), Scalar::Integer(1)),
(AttributeName::from("c"), Scalar::Integer(100)),
])
.unwrap(),
Tuple::try_from(vec![
(AttributeName::from("b"), Scalar::Integer(3)),
(AttributeName::from("c"), Scalar::Integer(300)),
])
.unwrap(),
Tuple::try_from(vec![
(AttributeName::from("b"), Scalar::Integer(5)),
(AttributeName::from("c"), Scalar::Integer(500)),
])
.unwrap(),
],
)
.unwrap();
assert_eq!(
relation.join(&other).unwrap(),
Relation::new_from_iter(
Heading::try_from(vec![
(AttributeName::from("a"), ScalarType::Boolean),
(AttributeName::from("b"), ScalarType::Integer),
(AttributeName::from("c"), ScalarType::Integer)
])
.unwrap(),
vec![
Tuple::try_from(vec![
(AttributeName::from("a"), Scalar::Boolean(true)),
(AttributeName::from("b"), Scalar::Integer(1)),
(AttributeName::from("c"), Scalar::Integer(100)),
])
.unwrap(),
Tuple::try_from(vec![
(AttributeName::from("a"), Scalar::Boolean(true)),
(AttributeName::from("b"), Scalar::Integer(3)),
(AttributeName::from("c"), Scalar::Integer(300)),
])
.unwrap(),
],
)
.unwrap()
);
}
#[test]
fn test_join_without_matches_is_empty() -> Result<(), Error> {
let lhs = Relation::new_from_iter(
Heading::try_from(vec![
(AttributeName::from("id"), ScalarType::Integer),
(AttributeName::from("left"), ScalarType::Integer),
])
.unwrap(),
vec![Tuple::try_from(vec![
(AttributeName::from("id"), Scalar::Integer(1)),
(AttributeName::from("left"), Scalar::Integer(10)),
])
.unwrap()],
)?;
let rhs = Relation::new_from_iter(
Heading::try_from(vec![
(AttributeName::from("id"), ScalarType::Integer),
(AttributeName::from("right"), ScalarType::Integer),
])
.unwrap(),
vec![Tuple::try_from(vec![
(AttributeName::from("id"), Scalar::Integer(2)),
(AttributeName::from("right"), Scalar::Integer(20)),
])
.unwrap()],
)?;
assert_eq!(
lhs.join(&rhs)?,
Relation::new_from_iter(
Heading::try_from(vec![
(AttributeName::from("id"), ScalarType::Integer),
(AttributeName::from("left"), ScalarType::Integer),
(AttributeName::from("right"), ScalarType::Integer),
])
.unwrap(),
Vec::new(),
)?
);
Ok(())
}
#[test]
fn test_join_without_common_attributes_behaves_like_product() -> Result<(), Error> {
let lhs = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("left"), ScalarType::Integer)]).unwrap(),
vec![Tuple::try_from(vec![(AttributeName::from("left"), Scalar::Integer(1))]).unwrap()],
)?;
let rhs = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("right"), ScalarType::Integer)]).unwrap(),
vec![
Tuple::try_from(vec![(AttributeName::from("right"), Scalar::Integer(2))]).unwrap(),
],
)?;
assert_eq!(lhs.join(&rhs)?, lhs.product(&rhs)?);
Ok(())
}
}