marsdb-query 0.5.0

openCypher query subset parser, planner, and executor used internally by MarsDB.
Documentation 
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use marsdb_graph::{Edge, Node, PropertyValue};

use crate::ast::Literal;

/// One element of a `Value::Path` — a path is `node, edge, node, edge,
/// ..., node`, alternating, as a single `Vec`, not two parallel node/edge
/// vecs (which would create an unenforced `nodes.len() == edges.len() +
/// 1` invariant across every place a path gets built or read).
#[derive(Debug, Clone)]
pub enum PathElem {
    Node(Node),
    Edge(Edge),
}

#[derive(Debug, Clone)]
pub enum Value {
    Node(Node),
    Edge(Edge),
    Property(PropertyValue),
    Literal(Literal),
    /// A `collect()` result — a query-layer-only concept, not persisted as
    /// a `PropertyValue` (nothing in the grammar can construct a list
    /// literal to store as a node/edge property).
    List(Vec<Value>),
    /// A named path (`MATCH p = (a)-->(b) RETURN p`) or a `shortestPath()`
    /// result — see `Binding::Path`'s docs (executor.rs) for how this
    /// gets assembled during MATCH evaluation.
    Path(Vec<PathElem>),
    Null,
}