# `AshNeo4j.Calculations.ProjectedTraversal`
[🔗](https://github.com/diffo-dev/ash_neo4j/blob/v0.10.1/lib/calculations/projected_traversal.ex#L5)

Read-time projection of a graph traversal (#329): follows a hop `chain` from
each record to the reached node and returns it as a value — late-binding the
reached node's concrete type at read time via `AshNeo4j.worlds/1`.

Use it where the reached node's concrete subtype isn't known at the source
resource's compile time (open-world refs across a cascade) — the read-time
sibling of the `traverse(^chain, …)` filter expression.

## Usage

    calculate :site, :struct,
      {AshNeo4j.Calculations.ProjectedTraversal,
       chain: [{:forward, :place_ref}, {:forward, :place}]}

## Options

  * `:chain` (required) — the hop chain, each hop `{:forward | :reverse,
    edge_selector}`, same grammar as the `traverse/2` expression.

## Result per record

  * the **concrete record** — a node was reached and its labels resolved to a
    loaded `(domain, resource)` world;
  * `%AshNeo4j.Unknown{reason: :no_concrete_world}` — a node was reached but
    its labels resolve to no loaded world (it can't be returned as a typed
    record);
  * `nil` — nothing was reached (genuine absence);
  * `%Ash.NotLoaded{}` — until the calculation is loaded.

v1 is single-valued (the first reached node) and projects the reached record;
list projection and single-field projection are follow-ups.

# `describe`

# `has_calculate?`

# `has_expression?`

# `init`

# `strict_loads?`

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*Consult [api-reference.md](api-reference.md) for complete listing*