codd 0.1.0

codd is a minimal in-memory database with relational algebraic expressions as queries.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55

use crate::{
    expression::{view::ViewRef, Expression, Relation, View, Visitor},
    Tuple,
};
use std::collections::HashSet;

/// Implements the `crate::expression::Visitor` to collect the relations and views to which
/// the visited expression depends.
pub(crate) struct DependencyVisitor {
    relations: HashSet<String>,
    views: HashSet<ViewRef>,
}

impl DependencyVisitor {
    /// Creates a new `Dependencies` visitor.
    pub fn new() -> Self {
        Self {
            relations: HashSet::new(),
            views: HashSet::new(),
        }
    }

    /// Consumes the reciever and returns a pair of relation and view dependencies.
    pub fn into_dependencies(self) -> (HashSet<String>, HashSet<ViewRef>) {
        (self.relations, self.views)
    }
}

impl Visitor for DependencyVisitor {
    fn visit_relation<T>(&mut self, relation: &Relation<T>)
    where
        T: Tuple,
    {
        self.relations.insert(relation.name().into());
    }

    fn visit_view<T, E>(&mut self, view: &View<T, E>)
    where
        T: Tuple,
        E: Expression<T>,
    {
        self.views.insert(view.reference().clone());
    }
}

pub(crate) fn expression_dependencies<T, E>(expression: &E) -> (HashSet<String>, HashSet<ViewRef>)
where
    T: Tuple,
    E: Expression<T>,
{
    let mut deps = DependencyVisitor::new();
    expression.visit(&mut deps);

    deps.into_dependencies()
}