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

Convenience helpers for creating the Neo4j VECTOR indexes that back
`AshNeo4j.Type.Vector` attributes.

Requires Cypher 25 (Neo4j ≥ 2025.06). Operations against an older server
return `{:error, %AshNeo4j.Error.RequiresCypher25{}}`.

    # Create the index for a vector attribute
    AshNeo4j.Vector.create_index(Item, :embedding)

    # Rebuild after a dimension or similarity-function change
    AshNeo4j.Vector.create_index(Item, :embedding, recreate: true)

    # Euclidean distance instead of the default cosine
    AshNeo4j.Vector.create_index(Item, :embedding, similarity_function: :euclidean)

Consistent with AshNeo4j's "no automatic migrations" stance — this is an
ergonomic tool you call (e.g. from a start-up task). `create_index/3` uses
`IF NOT EXISTS`, so it is safe to run repeatedly.

## Naming

The index is named `<base>_vector` where `base` defaults to
`<label_lower>_<property>` — e.g. `item_embedding_vector`. Pass `:name` to
override the base.

## Dry run

`index_statements/3` returns the `CREATE` Cypher without touching the
database — useful for review or testing.

# `create_index`

```elixir
@spec create_index(Ash.Resource.t(), atom(), keyword()) ::
  {:ok, Bolty.Response.t()} | {:error, term()}
```

Creates the VECTOR index for `attr` on `resource`.

Returns `{:ok, %Bolty.Response{}}` or `{:error, reason}`.

## Options

  * `:recreate` — `DROP INDEX ... IF EXISTS` before `CREATE`. Use after changing
    `:dimensions` or `:similarity_function`. Defaults to `false`.
  * `:name` — override the auto-derived base name. `_vector` is still appended.
  * `:similarity_function` — `:cosine` (default) or `:euclidean`.

# `drop_index`

```elixir
@spec drop_index(Ash.Resource.t(), atom(), keyword()) ::
  {:ok, Bolty.Response.t()} | {:error, term()}
```

Drops the VECTOR index for `attr`. Uses `IF EXISTS`, so it is a no-op when absent.

# `index_statements`

```elixir
@spec index_statements(Ash.Resource.t(), atom(), keyword()) ::
  {:ok, String.t()} | {:error, term()}
```

Returns `{:ok, statement}` — the `CREATE VECTOR INDEX` Cypher that
`create_index/3` would run — without touching the database.

    AshNeo4j.Vector.index_statements(Item, :embedding)
    #=> {:ok, "CREATE VECTOR INDEX item_embedding_vector IF NOT EXISTS FOR (n:Item) ON (n.embedding) OPTIONS {indexConfig: {`vector.dimensions`: 1536, `vector.similarity_function`: 'cosine'}}"}

---

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