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[#88] Nebulex.Adapters.Nil adapter for disabling cache
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,148 @@ | ||
| defmodule Nebulex.Adapters.Nil do | ||
| @moduledoc """ | ||
| The **Nil adapter** is a special cache adapter that disables the cache; | ||
| it loses all the items saved on it and it returns `nil` for all the read | ||
| and `true` for all save operations. This adapter is mostly useful for tests. | ||
| ## Example | ||
| Suppose you have an application using Ecto for database access and Nebulex | ||
| for caching. Then, you have defined a cache and a repo within it. Since you | ||
| are using a database, there might be some cases you may want to disable the | ||
| cache to avoid issues when running the test, for example, in some test cases, | ||
| when accessing the database you expect no data at all, but you could retrieve | ||
| the data from cache anyway because maybe it was cached in a previous test. | ||
| Therefore, you have to flush the cache before to run each test to make sure | ||
| the data is always empty. This is where the Nil adapter comes in, instead of | ||
| adding code to flush the cache before each test, you could define a test cache | ||
| using the Nil adapter for the tests. | ||
| One one hand, you have defined the cache in your application within | ||
| `lib/my_app/cache.ex`: | ||
| defmodule MyApp.Cache do | ||
| use Nebulex.Cache, | ||
| otp_app: :my_app, | ||
| adapter: Nebulex.Adapters.Local | ||
| end | ||
| And on the other hand, in the tests you have defined the test cache within | ||
| `test/support/test_cache.ex`: | ||
| defmodule MyApp.TestCache do | ||
| use Nebulex.Cache, | ||
| otp_app: :my_app, | ||
| adapter: Nebulex.Adapters.Nil | ||
| end | ||
| Now, we have to tell the app what cache to use depending on the environment, | ||
| for tests we want `MyApp.TestCache`, otherwise it is always `MyApp.Cache`. | ||
| We can do this very easy by introducing a new config parameter to decide | ||
| what cache module to use. For tests you can define the config | ||
| `config/test.exs`: | ||
| config :my_app, | ||
| nebulex_cache: MyApp.TestCache, | ||
| ... | ||
| The final piece is to read the config parameter and start the cache properly. | ||
| Within `lib/my_app/application.ex` you could have: | ||
| def start(_type, _args) do | ||
| children = [ | ||
| {Application.get_env(:my_app, :nebulex_cache, MyApp.Cache), []}, | ||
| ] | ||
| ... | ||
| As you can see, by default `MyApp.Cache` is always used, unless the | ||
| `:nebulex_cache` option points to a different module, which will be | ||
| when tests are executed (`:test` env). | ||
| """ | ||
|
|
||
| # Provide Cache Implementation | ||
| @behaviour Nebulex.Adapter | ||
| @behaviour Nebulex.Adapter.Entry | ||
| @behaviour Nebulex.Adapter.Storage | ||
| @behaviour Nebulex.Adapter.Queryable | ||
| @behaviour Nebulex.Adapter.Persistence | ||
| @behaviour Nebulex.Adapter.Stats | ||
|
|
||
| # Inherit default transaction implementation | ||
| use Nebulex.Adapter.Transaction | ||
|
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||
| ## Nebulex.Adapter | ||
|
|
||
| @impl true | ||
| defmacro __before_compile__(_env), do: :ok | ||
|
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| @impl true | ||
| def init(_opts) do | ||
| child_spec = Supervisor.child_spec({Agent, fn -> :ok end}, id: {Agent, 1}) | ||
| {:ok, child_spec, %{}} | ||
| end | ||
|
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| ## Nebulex.Adapter.Entry | ||
|
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| @impl true | ||
| def get(_, _, _), do: nil | ||
|
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| @impl true | ||
| def get_all(_, _, _), do: %{} | ||
|
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| @impl true | ||
| def put(_, _, _, _, _, _), do: true | ||
|
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| @impl true | ||
| def put_all(_, _, _, _, _), do: true | ||
|
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| @impl true | ||
| def delete(_, _, _), do: :ok | ||
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| @impl true | ||
| def take(_, _, _), do: nil | ||
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| @impl true | ||
| def has_key?(_, _), do: false | ||
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| @impl true | ||
| def ttl(_, _), do: nil | ||
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| @impl true | ||
| def expire(_, _, _), do: true | ||
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| @impl true | ||
| def touch(_, _), do: true | ||
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| @impl true | ||
| def incr(_, _, _, _, _), do: 1 | ||
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| ## Nebulex.Adapter.Storage | ||
|
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| @impl true | ||
| def size(_), do: 0 | ||
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| @impl true | ||
| def flush(_), do: 0 | ||
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| ## Nebulex.Adapter.Queryable | ||
|
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| @impl true | ||
| def all(_, _, _), do: [] | ||
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| @impl true | ||
| def stream(_, _, _), do: Stream.each([], & &1) | ||
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| ## Nebulex.Adapter.Persistence | ||
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| @impl true | ||
| def dump(_, _, _), do: :ok | ||
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| @impl true | ||
| def load(_, _, _), do: :ok | ||
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| ## Nebulex.Adapter.Stats | ||
|
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| @impl true | ||
| def stats_info(_), do: %Nebulex.Stats{} | ||
| end |
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