91 lines
2.5 KiB
Rust
91 lines
2.5 KiB
Rust
//! Binding relations: rows over named (variable) columns.
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//!
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//! Every operator in this crate (after the initial atom scan) consumes and
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//! produces [`Relation`]s. Column names are variable names; a value at column
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//! `i` of a row is the value bound to variable `columns[i]` in that solution.
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//!
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//! Column names within a single relation must be unique. Constructors enforce
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//! this invariant; downstream operators rely on it when matching shared columns
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//! across two relations.
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use std::collections::HashSet;
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use crate::value::Value;
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#[derive(Debug, Clone)]
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pub struct Relation {
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pub columns: Vec<String>,
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pub rows: Vec<Vec<Value>>,
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}
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fn assert_unique_columns(columns: &[String]) {
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let mut seen: HashSet<&str> = HashSet::with_capacity(columns.len());
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for name in columns {
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assert!(
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seen.insert(name.as_str()),
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"duplicate column name in relation: {name}",
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);
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}
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}
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impl Relation {
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/// # Panics
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/// Panics if `columns` contains a duplicate name.
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#[must_use]
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pub fn new(columns: Vec<String>) -> Self {
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assert_unique_columns(&columns);
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Self {
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columns,
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rows: Vec::new(),
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}
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}
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/// # Panics
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/// Panics if `columns` contains a duplicate name, or if any row's length
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/// differs from `columns.len()`.
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#[must_use]
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pub fn from_rows(columns: Vec<String>, rows: Vec<Vec<Value>>) -> Self {
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assert_unique_columns(&columns);
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let arity = columns.len();
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for (i, row) in rows.iter().enumerate() {
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assert_eq!(
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row.len(),
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arity,
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"row {i} arity mismatch: expected {arity}, got {}",
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row.len(),
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);
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}
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Self { columns, rows }
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}
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/// # Panics
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/// Panics if `row.len() != self.columns.len()`.
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pub fn push(&mut self, row: Vec<Value>) {
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assert_eq!(
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row.len(),
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self.columns.len(),
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"row arity mismatch: expected {}, got {}",
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self.columns.len(),
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row.len(),
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);
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self.rows.push(row);
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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#[should_panic(expected = "duplicate column name")]
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fn from_rows_rejects_duplicate_column_names() {
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let _ = Relation::from_rows(vec!["X".to_string(), "X".to_string()], vec![]);
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}
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#[test]
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#[should_panic(expected = "duplicate column name")]
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fn new_rejects_duplicate_column_names() {
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let _ = Relation::new(vec!["X".to_string(), "X".to_string()]);
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}
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}
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