# `AshCache.Preparations.ReadThrough`
[🔗](https://github.com/Undeadlol1/ash_cache/blob/v0.1.0/lib/ash_cache/preparations/read_through.ex#L1)

Read-through caching for a read action.

On a cache hit the query result is set via `Ash.Query.set_result/2`, so
the data layer is never called. On a miss, an `after_action` hook caches
the records the action returns.

The cache key is derived inside a `before_action` hook, not at
preparation time: preparations run before the framework has applied
everything that shapes the result — a `get_by` code interface, for
example, attaches its primary-key filter after preparations, so a key
derived earlier would collide the get with the unfiltered read.

Safety properties:

  * the cache key embeds actor and tenant (`AshCache.Key`), so a hit can
    only return records the same actor/tenant already read through the
    action's full authorization
  * empty results (`[]`/`nil`) are not cached unless `cache_empty?: true`,
    preventing a transient miss from being served for a whole TTL
  * `Ash.Query.set_context(query, %{ash_cache: :bypass})` skips the cache
    for one query
  * identical misses running at once share one data-layer read
    (`AshCache.Coalesce`). The leader's lease is released in an
    `around_transaction` hook, which wraps the whole read, so a failed or
    raising read still lets its waiters go

# `init`

# `supports`

---

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