Add query_cache option to selectively bypass query cache (#4690)

Author: rbino

lib/ecto/adapter/queryable.ex

@@ -98,16 +98,19 @@ defmodule Ecto.Adapter.Queryable do
   @doc """
   Plans and prepares a query for the given repo, leveraging its query cache.
 
-  This operation uses the query cache if one is available.
+  This operation uses the query cache if one is available, unless
+  `query_cache: false` is passed as option, which bypasses the query cache.
   """
-  def prepare_query(operation, repo_name_or_pid, queryable) do
+  def prepare_query(operation, repo_name_or_pid, queryable, opts \\ []) do
     %{adapter: adapter, cache: cache} = Ecto.Repo.Registry.lookup(repo_name_or_pid)
 
+    query_cache? = Keyword.get(opts, :query_cache, true)
+
     {_meta, prepared, _cast_params, dump_params} =
       queryable
       |> Ecto.Queryable.to_query()
       |> Ecto.Query.Planner.ensure_select(operation == :all)
-      |> Ecto.Query.Planner.query(operation, cache, adapter, 0)
+      |> Ecto.Query.Planner.query(operation, cache, adapter, 0, query_cache?)
 
     {prepared, dump_params}
   end

lib/ecto/query/planner.ex

@@ -133,9 +133,10 @@ defmodule Ecto.Query.Planner do
   The cache value is the compiled query by the adapter
   along-side the select expression.
   """
-  def query(query, operation, cache, adapter, counter) do
+  def query(query, operation, cache, adapter, counter, query_cache?) do
     {query, params, key} = plan(query, operation, adapter)
     {cast_params, dump_params} = Enum.unzip(params)
+    key = if query_cache?, do: key, else: :nocache
     query_with_cache(key, query, operation, cache, adapter, counter, cast_params, dump_params)
   end
 

lib/ecto/repo.ex

@@ -136,6 +136,11 @@ defmodule Ecto.Repo do
       See the next section for more information
     * `:telemetry_options` - Extra options to attach to telemetry event name.
       See the next section for more information
+    * `:query_cache` - When set to `false`, bypasses the Ecto query cache for the current
+      operation. This means the query will not be looked up in the cache, it will not be stored
+      in the cache and no cache update function will not be passed to the adapter. Note that
+      this doesn't necessarily disable the database cache, it only affects Ecto's internal
+      cache of normalized queries and adapter prepared statements. Defaults to `true`.
 
   ## Adapter-Specific Errors
 

lib/ecto/repo/queryable.ex

@@ -39,8 +39,10 @@ defmodule Ecto.Repo.Queryable do
     {query, opts} = repo.prepare_query(:stream, query, opts)
     query = attach_prefix(query, opts)
 
+    query_cache? = Keyword.get(opts, :query_cache, true)
+
     {query_meta, prepared, cast_params, dump_params} =
-      Planner.query(query, :all, cache, adapter, 0)
+      Planner.query(query, :all, cache, adapter, 0, query_cache?)
 
     opts = [cast_params: cast_params] ++ opts
 
@@ -223,8 +225,10 @@ defmodule Ecto.Repo.Queryable do
     {query, opts} = repo.prepare_query(operation, query, opts)
     query = attach_prefix(query, opts)
 
+    query_cache? = Keyword.get(opts, :query_cache, true)
+
     {query_meta, prepared, cast_params, dump_params} =
-      Planner.query(query, operation, cache, adapter, 0)
+      Planner.query(query, operation, cache, adapter, 0, query_cache?)
 
     opts = [cast_params: cast_params] ++ opts
 

test/ecto/query/planner_test.exs

@@ -2829,4 +2829,29 @@ defmodule Ecto.Query.PlannerTest do
       end
     end
   end
+
+  describe "query: query_cache option" do
+    setup do
+      cache = Planner.new_query_cache(__MODULE__)
+      {:ok, cache: cache}
+    end
+
+    test "uses cache if true", %{cache: cache} do
+      query = from(p in Post, where: p.title == ^"hello")
+
+      {_meta, {:cache, _update, _prepared}, _cast, _dump} =
+        Planner.query(query, :all, cache, Ecto.CachingTestAdapter, 0, true)
+
+      assert :ets.info(cache, :size) == 1
+    end
+
+    test "bypasses cache if false", %{cache: cache} do
+      query = from(p in Post, where: p.title == ^"hello")
+
+      {_meta1, {:nocache, _prepared}, _cast1, _dump1} =
+        Planner.query(query, :all, cache, Ecto.CachingTestAdapter, 0, false)
+
+      assert :ets.info(cache, :size) == 0
+    end
+  end
 end

test/support/test_repo.exs

@@ -161,6 +161,46 @@ defmodule Ecto.TestAdapter do
   end
 end
 
+defmodule Ecto.CachingTestAdapter do
+  @moduledoc """
+  Test adapter that supports query caching, used for testing the query_cache option.
+  """
+  @behaviour Ecto.Adapter
+  @behaviour Ecto.Adapter.Queryable
+
+  defmacro __before_compile__(_opts), do: :ok
+
+  def ensure_all_started(_, _), do: {:ok, []}
+
+  def init(_opts) do
+    {:ok, Supervisor.child_spec({Task, fn -> :timer.sleep(:infinity) end}, []), %{}}
+  end
+
+  def checkout(_mod, _opts, fun), do: fun.()
+  def checked_out?(_mod), do: false
+
+  def loaders(_primitive, type), do: [type]
+  def dumpers(_primitive, type), do: [type]
+  def autogenerate(:id), do: nil
+  def autogenerate(:embed_id), do: Ecto.UUID.autogenerate()
+  def autogenerate(:binary_id), do: Ecto.UUID.bingenerate()
+
+  # Return :cache to trigger default caching in the planner
+  def prepare(operation, query), do: {:cache, {operation, query}}
+
+  def execute(_adapter_meta, _query_meta, {_cache_status, {:all, _query}}, _dump_params, _opts) do
+    []
+  end
+
+  def execute(_adapter_meta, _query_meta, {_cache_status, {_operation, _query}}, _dump_params, _opts) do
+    {1, nil}
+  end
+
+  def stream(_adapter_meta, _query_meta, _prepared, _dump_params, _opts) do
+    []
+  end
+end
+
 Application.put_env(:ecto, Ecto.TestRepo, user: "invalid")
 
 defmodule Ecto.TestRepo do