Allow MyXQL to specify :prepare per operation.

integration_test/myxql/prepare_test.exs

@@ -0,0 +1,36 @@
+defmodule Ecto.Integration.PrepareTest do
+  use Ecto.Integration.Case, async: false
+
+  import Ecto.Query, only: [from: 2]
+
+  alias Ecto.Integration.TestRepo
+  alias Ecto.Integration.Post
+
+  test "prepare option" do
+    TestRepo.insert!(%Post{title: "one"})
+
+    query = from p in Post, select: fragment("'mxql test prepare option'")
+    stmt_count_query = "SHOW GLOBAL STATUS LIKE '%prepared_stmt_count%'"
+
+    %{rows: [[_, orig_count]]} = TestRepo.query!(stmt_count_query, [])
+    orig_count = String.to_integer(orig_count)
+
+    # Uncached
+    assert TestRepo.all(query, prepare: :unnamed) == ["mxql test prepare option"]
+    %{rows: [[_, new_count]]} = TestRepo.query!(stmt_count_query, [])
+    assert String.to_integer(new_count) == orig_count
+
+    assert TestRepo.all(query, prepare: :named) == ["mxql test prepare option"]
+    assert %{rows: [[_, new_count]]} = TestRepo.query!(stmt_count_query, [])
+    assert String.to_integer(new_count) == orig_count + 1
+
+    # Cached
+    assert TestRepo.all(query, prepare: :unnamed) == ["mxql test prepare option"]
+    assert %{rows: [[_, new_count]]} = TestRepo.query!(stmt_count_query, [])
+    assert String.to_integer(new_count) == orig_count + 1
+
+    assert TestRepo.all(query, prepare: :named) == ["mxql test prepare option"]
+    assert %{rows: [[_, new_count]]} = TestRepo.query!(stmt_count_query, [])
+    assert String.to_integer(new_count) == orig_count + 1
+  end
+end

lib/ecto/adapters/myxql.ex

@@ -10,6 +10,13 @@ defmodule Ecto.Adapters.MyXQL do
   below. All options can be given via the repository
   configuration:
 
+      config :your_app, YourApp.Repo,
+        ...
+
+  The `:prepare` option may be specified per operation:
+
+      YourApp.Repo.all(Queryable, prepare: :unnamed)
+
   ### Connection options
 
     * `:protocol` - Set to `:socket` for using UNIX domain socket, or `:tcp` for TCP
@@ -147,6 +154,8 @@ defmodule Ecto.Adapters.MyXQL do
   @behaviour Ecto.Adapter.Storage
   @behaviour Ecto.Adapter.Structure
 
+  @default_prepare_opt :named
+
   ## Custom MySQL types
 
   @impl true
@@ -171,6 +180,23 @@ defmodule Ecto.Adapters.MyXQL do
   defp json_decode(x) when is_binary(x), do: {:ok, MyXQL.json_library().decode!(x)}
   defp json_decode(x), do: {:ok, x}
 
+  ## Query API
+
+  @impl Ecto.Adapter.Queryable
+  def execute(adapter_meta, query_meta, query, params, opts) do
+    prepare = Keyword.get(opts, :prepare, @default_prepare_opt)
+
+    unless valid_prepare?(prepare) do
+      raise ArgumentError,
+            "expected option `:prepare` to be either `:named` or `:unnamed`, got: #{inspect(prepare)}"
+    end
+
+    Ecto.Adapters.SQL.execute(prepare, adapter_meta, query_meta, query, params, opts)
+  end
+
+  defp valid_prepare?(prepare) when prepare in [:named, :unnamed], do: true
+  defp valid_prepare?(_), do: false
+
   ## Storage API
 
   @impl true