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use crate::{
error::Error,
prelude::{Heading, Relation, Tuple},
};
impl Heading {
pub(crate) fn product(&self, other: &Heading) -> Result<Heading, Error> {
let mut attributes = self.attributes.clone();
for (name, ty) in &other.attributes {
if attributes.contains_key(name) {
return Err(Error::AttributeAlreadyExists { name: name.clone() });
}
attributes.insert(name.clone(), *ty);
}
Ok(Heading::new(attributes))
}
}
impl Tuple {
pub(crate) fn product(&self, other: &Tuple) -> Result<Tuple, Error> {
let mut values = self.values.clone();
for (name, value) in &other.values {
if values.contains_key(name) {
return Err(Error::AttributeAlreadyExists { name: name.clone() });
}
values.insert(name.clone(), value.clone());
}
Ok(Tuple::from(values))
}
}
impl Relation {
/// Returns the Cartesian product of two relations (`×`).
///
/// `colors`
///
/// | `left` |
/// | --- |
/// | `1` |
/// | `2` |
///
/// `sizes`
///
/// | `right` |
/// | --- |
/// | `10` |
/// | `20` |
///
/// Output
///
/// | `left` | `right` |
/// | --- | --- |
/// | `1` | `10` |
/// | `1` | `20` |
/// | `2` | `10` |
/// | `2` | `20` |
///
/// # Errors
///
/// Returns [`Error::AttributeAlreadyExists`] if both relations contain the
/// same attribute name, making the Cartesian product ambiguous.
///
/// # Example
///
/// ```rust
/// use darwen::prelude::{AttributeName, Heading, Relation, Scalar, ScalarType, Tuple};
///
/// let colors = Relation::new_from_iter(
/// Heading::try_from(vec![(AttributeName::from("left"), ScalarType::Integer)])?,
/// vec![
/// Tuple::try_from(vec![(AttributeName::from("left"), Scalar::Integer(1))])?,
/// Tuple::try_from(vec![(AttributeName::from("left"), Scalar::Integer(2))])?,
/// ],
/// )?;
/// let sizes = Relation::new_from_iter(
/// Heading::try_from(vec![(AttributeName::from("right"), ScalarType::Integer)])?,
/// vec![
/// Tuple::try_from(vec![(AttributeName::from("right"), Scalar::Integer(10))])?,
/// Tuple::try_from(vec![(AttributeName::from("right"), Scalar::Integer(20))])?,
/// ],
/// )?;
///
/// let combinations = colors.product(&sizes)?;
///
/// assert_eq!(
/// combinations,
/// Relation::new_from_iter(
/// Heading::try_from(vec![
/// (AttributeName::from("left"), ScalarType::Integer),
/// (AttributeName::from("right"), ScalarType::Integer),
/// ])?,
/// vec![
/// Tuple::try_from(vec![
/// (AttributeName::from("left"), Scalar::Integer(1)),
/// (AttributeName::from("right"), Scalar::Integer(10)),
/// ])?,
/// Tuple::try_from(vec![
/// (AttributeName::from("left"), Scalar::Integer(1)),
/// (AttributeName::from("right"), Scalar::Integer(20)),
/// ])?,
/// Tuple::try_from(vec![
/// (AttributeName::from("left"), Scalar::Integer(2)),
/// (AttributeName::from("right"), Scalar::Integer(10)),
/// ])?,
/// Tuple::try_from(vec![
/// (AttributeName::from("left"), Scalar::Integer(2)),
/// (AttributeName::from("right"), Scalar::Integer(20)),
/// ])?,
/// ],
/// )?
/// );
/// # Ok::<(), darwen::prelude::Error>(())
/// ```
pub fn product(&self, other: &Relation) -> Result<Relation, Error> {
let heading = self.heading.product(&other.heading)?;
let mut relation = Relation::new(heading);
for t in &self.body {
for u in &other.body {
relation.body.insert(t.product(u)?);
}
}
Ok(relation)
}
}
#[cfg(test)]
mod tests {
use crate::{
prelude::{Heading, Scalar, ScalarType, Tuple},
types::AttributeName,
};
use super::*;
#[test]
fn test_product() {
let relation = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(1))]).unwrap(),
Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(2))]).unwrap(),
],
)
.unwrap();
let other = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("bar"), ScalarType::Boolean)]).unwrap(),
vec![
Tuple::try_from(vec![(AttributeName::from("bar"), Scalar::Boolean(true))]).unwrap(),
Tuple::try_from(vec![(AttributeName::from("bar"), Scalar::Boolean(false))])
.unwrap(),
],
)
.unwrap();
assert_eq!(
relation.product(&other).unwrap(),
Relation::new_from_iter(
Heading::try_from(vec![
(AttributeName::from("foo"), ScalarType::Integer),
(AttributeName::from("bar"), ScalarType::Boolean)
])
.unwrap(),
vec![
Tuple::try_from(vec![
(AttributeName::from("foo"), Scalar::Integer(1)),
(AttributeName::from("bar"), Scalar::Boolean(true))
])
.unwrap(),
Tuple::try_from(vec![
(AttributeName::from("foo"), Scalar::Integer(1)),
(AttributeName::from("bar"), Scalar::Boolean(false))
])
.unwrap(),
Tuple::try_from(vec![
(AttributeName::from("foo"), Scalar::Integer(2)),
(AttributeName::from("bar"), Scalar::Boolean(true))
])
.unwrap(),
Tuple::try_from(vec![
(AttributeName::from("foo"), Scalar::Integer(2)),
(AttributeName::from("bar"), Scalar::Boolean(false))
])
.unwrap(),
],
)
.unwrap()
);
}
#[test]
fn test_product_with_empty_relation_is_empty() -> Result<(), Error> {
let lhs = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(1))]).unwrap()],
)?;
let rhs = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("bar"), ScalarType::Boolean)]).unwrap(),
Vec::new(),
)?;
assert_eq!(
lhs.product(&rhs)?,
Relation::new_from_iter(
Heading::try_from(vec![
(AttributeName::from("foo"), ScalarType::Integer),
(AttributeName::from("bar"), ScalarType::Boolean),
])
.unwrap(),
Vec::new(),
)?
);
Ok(())
}
#[test]
fn test_product_rejects_overlapping_attributes() -> Result<(), Error> {
let lhs = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(1))]).unwrap()],
)?;
let rhs = Relation::new_from_iter(
Heading::try_from(vec![(AttributeName::from("foo"), ScalarType::Integer)]).unwrap(),
vec![Tuple::try_from(vec![(AttributeName::from("foo"), Scalar::Integer(2))]).unwrap()],
)?;
assert_eq!(
lhs.product(&rhs),
Err(Error::AttributeAlreadyExists { name: "foo".into() })
);
Ok(())
}
#[test]
fn test_tuple_product_rejects_overlapping_attributes() {
let lhs = Tuple::try_from(vec![
(AttributeName::from("foo"), Scalar::Integer(1)),
(AttributeName::from("shared"), Scalar::Integer(10)),
])
.unwrap();
let rhs = Tuple::try_from(vec![
(AttributeName::from("bar"), Scalar::Boolean(true)),
(AttributeName::from("shared"), Scalar::Integer(20)),
])
.unwrap();
assert_eq!(
lhs.product(&rhs),
Err(Error::AttributeAlreadyExists {
name: "shared".into()
})
);
}
}