Support explain format option for myxql (#454)

Author: vorce

integration_test/myxql/explain_test.exs

@@ -34,5 +34,13 @@ defmodule Ecto.Integration.ExplainTest do
         TestRepo.explain(:all, from(p in "posts", select: p.invalid, where: p.invalid == "title"))
       end)
     end
+
+    test "map format" do
+      [explain] = TestRepo.explain(:all, Post, format: :map)
+      keys = explain["query_block"] |> Map.keys
+      assert Enum.member?(keys, "cost_info")
+      assert Enum.member?(keys, "select_id")
+      assert Enum.member?(keys, "table")
+    end
   end
 end

lib/ecto/adapters/myxql/connection.ex

@@ -222,10 +222,18 @@ if Code.ensure_loaded?(MyXQL) do
     end
 
     @impl true
-    # DB explain opts are deprecated, so they aren't used to build the explain query.
+    # DB explain opts, except format, are deprecated.
     # See Notes at https://dev.mysql.com/doc/refman/5.7/en/explain.html
     def explain_query(conn, query, params, opts) do
-      case query(conn, build_explain_query(query), params, opts) do
+      {explain_opts, opts} = Keyword.split(opts, ~w[format]a)
+      map_format? = {:format, :map} in explain_opts
+
+      case query(conn, build_explain_query(query, explain_opts), params, opts) do
+        {:ok, %MyXQL.Result{rows: rows}} when map_format? ->
+          json_library = MyXQL.json_library()
+          decoded_result = Enum.map(rows, &json_library.decode!(&1))
+          {:ok, decoded_result}
+
         {:ok, %MyXQL.Result{} = result} ->
           {:ok, SQL.format_table(result)}
 
@@ -234,11 +242,16 @@ if Code.ensure_loaded?(MyXQL) do
       end
     end
 
-    def build_explain_query(query) do
+    def build_explain_query(query, []) do
       ["EXPLAIN ", query]
       |> IO.iodata_to_binary()
     end
 
+    def build_explain_query(query, [format: value]) do
+      ["EXPLAIN #{String.upcase("#{format_to_sql(value)}")} ", query]
+      |> IO.iodata_to_binary()
+    end
+
     ## Query generation
 
     binary_ops =
@@ -1080,6 +1093,9 @@ if Code.ensure_loaded?(MyXQL) do
       [?`, name, ?`]
     end
 
+    defp format_to_sql(:map), do: "FORMAT=JSON"
+    defp format_to_sql(:text), do: "FORMAT=TRADITIONAL"
+
     defp intersperse_map(list, separator, mapper, acc \\ [])
     defp intersperse_map([], _separator, _mapper, acc),
       do: acc

lib/ecto/adapters/sql.ex

@@ -320,8 +320,9 @@ defmodule Ecto.Adapters.SQL do
   Also note that:
 
     * Currently `:map`, `:yaml`, and `:text` format options are supported
-      for PostgreSQL. `:map` is the deserialized JSON encoding. The last two
-      options return the result as a string;
+      for PostgreSQL. Only `map` and `text` are supported for MyXQL.
+      * `:map` is the deserialized JSON encoding.
+      * `:yaml` and `text` return the result as a string;
 
     * Any other value passed to `opts` will be forwarded to the underlying
       adapter query function, including Repo shared options such as `:timeout`;

test/ecto/adapters/myxql_test.exs

@@ -719,7 +719,8 @@ defmodule Ecto.Adapters.MyXQLTest do
   end
 
   test "build_explain_query" do
-    assert SQL.build_explain_query("SELECT 1") == "EXPLAIN SELECT 1"
+    assert SQL.build_explain_query("SELECT 1", []) == "EXPLAIN SELECT 1"
+    assert SQL.build_explain_query("SELECT 1", format: :map) == "EXPLAIN FORMAT=JSON SELECT 1"
   end
 
   ## *_all