Struct HashMapJunction 

pub struct HashMapJunction { /* private fields */ }

One relationship’s junction: each source id mapped to its ordered target ids.

The junction of an exclusive relationship (one-to-one, one-to-many, ordered one-to-many) also keeps a reverse index, target to the sources holding it, so that “this target already belongs to another source” costs one lookup per target of a write instead of a walk over every row of the relationship. Without it, creating N rows that each own a child is O(N²).

The rows are private, so nothing can change them behind the index: every mutation goes through Self::insert, Self::remove or Self::remove_target, which update both in the same call, and a whole-junction clone (snapshot, savepoint, HashMapStore::freeze, restore) carries both together. Both are im::HashMaps, so that clone stays O(1).

The read methods mirror the map it wraps (get, iter, contains_key, …), so code that only reads a junction reads it as before.

Implementations

impl HashMapJunction

pub fn exclusive() -> Self

An empty junction for an exclusive relationship, with its reverse index.

pub fn shared() -> Self

An empty junction for a shared relationship, without a reverse index.

pub fn is_exclusive(&self) -> bool

Whether this junction belongs to an exclusive relationship.

pub fn get(&self, source: &EntityId) -> Option<&Vec<EntityId>>

The ordered targets of source, if it has a row.

pub fn contains_key(&self, source: &EntityId) -> bool

Whether source has a row (possibly empty).

pub fn iter(&self) -> impl Iterator<Item = (&EntityId, &Vec<EntityId>)>

Every row, as (source, targets), in no particular order.

pub fn keys(&self) -> impl Iterator<Item = &EntityId>

Every source that has a row, in no particular order.

pub fn values(&self) -> impl Iterator<Item = &Vec<EntityId>>

Every row’s targets, in no particular order.

pub fn len(&self) -> usize

The number of rows.

pub fn is_empty(&self) -> bool

Whether the junction has no row at all.

pub fn sources_of(&self, target: &EntityId) -> Vec<EntityId>

Every source whose row holds target, once per occurrence: none or one in a consistent exclusive junction. One lookup on an exclusive junction; a walk over every row on a shared one, which has no index.

pub fn insert( &mut self, source: EntityId, targets: Vec<EntityId>, ) -> Option<Vec<EntityId>>

Replace the row of source with targets, returning the previous row.

pub fn remove(&mut self, source: &EntityId) -> Option<Vec<EntityId>>

Remove the row of source, returning it.

pub fn remove_target(&mut self, target: &EntityId)

Remove target from every row holding it, as when the target entity is deleted. Visits only those rows on an exclusive junction, every row on a shared one.

pub fn check_index(&self) -> Result<(), String>

Compare the reverse index with one rebuilt from the rows.

A diagnostic for tests, O(junction): see HashMapStore::check_junction_indexes. A shared junction has no index and always passes.

Trait Implementations

impl Clone for HashMapJunction

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for HashMapJunction

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for HashMapJunction

fn default() -> Self

Returns the “default value” for a type.