Struct Via 

pub struct Via {
    pub target: ModelId,
    pub expr_ty: Type,
    pub cardinality: Cardinality,
    pub path: Path,
    pub terminal: Option<usize>,
}

A multi-step relation path.

A Has relation declared with #[has_many(via = a.b)] or #[has_one(via = a.b)] reaches its target by following a path of existing relations rather than pairing with a single BelongsTo. The path is resolved at macro-expansion time — the derive emits a chained call on the model’s Fields struct (e.g. User::fields().comments().article()) and converts it into a stmt::Path, so a misspelled or otherwise unresolvable segment is a Rust compile error rather than a runtime schema validation failure.

The terminal segment of the path is usually another relation (the via reaches a model). It may also be a scalar field, in which case the via projects that field through the relation path — e.g. #[has_many(via = todos.tags.name)] tag_names: Vec<String> collects the name of every tag reachable through todos. For a scalar terminal, terminal holds the terminal field’s index on target (the model the relation chain reaches), and path still includes that terminal step as its last element.

Fields

target: ModelId

The ModelId of the model the relation chain reaches. For a relation terminal this is the associated (target) model; for a scalar terminal it is the model that owns the projected terminal field.

expr_ty: Type

The expression type this field evaluates to from the application’s perspective.

cardinality: Cardinality

Whether this relation is one-to-many or one-to-one.

path: Path

The resolved field path, rooted at the model that declares the via relation. When terminal is Some, the last element of the path is the scalar terminal field (on target) and the preceding elements form the relation chain.

terminal: Option<usize>

For a scalar-terminal via, the index of the projected terminal field on target. None when the via reaches a model (the terminal segment is itself a relation).

Implementations

impl Via

pub fn new( target: ModelId, expr_ty: Type, cardinality: Cardinality, path: Path, terminal: Option<usize>, ) -> Self

Create a Via from its fully resolved field path.

pub fn is_scalar(&self) -> bool

Returns true when the via projects a scalar terminal field rather than reaching a model.

pub fn is_many(&self) -> bool

Returns true when this is a one-to-many relation.

pub fn is_one(&self) -> bool

Returns true when this is a one-to-one relation.

pub fn singular(&self) -> Option<&Name>

Returns the singular item name for a one-to-many relation.

pub fn target<'a>(&self, schema: &'a Schema) -> &'a Model

Resolves the target Model from the given schema.

Trait Implementations

impl Clone for Via

fn clone(&self) -> Via

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Via

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

Formats the value using the given formatter.