Escape backslashes in MySQL JSON path keys (#759)

Author: ybai08

lib/ecto/adapters/myxql/connection.ex

@@ -1629,8 +1629,9 @@ if Code.ensure_loaded?(MyXQL) do
 
     defp escape_json_key(value) when is_binary(value) do
       value
+      |> :binary.replace("\\", "\\\\", [:global])
+      |> :binary.replace("\"", "\\\"", [:global])
       |> escape_string()
-      |> :binary.replace("\"", "\\\\\"", [:global])
     end
 
     defp ecto_cast_to_db(:id, _query), do: "unsigned"

test/ecto/adapters/myxql_test.exs

@@ -824,6 +824,12 @@ defmodule Ecto.Adapters.MyXQLTest do
 
     query = Schema |> select([s], json_extract_path(s.meta, ["\"a"])) |> plan()
     assert all(query) == ~s{SELECT json_extract(s0.`meta`, '$."\\\\"a"') FROM `schema` AS s0}
+
+    query = Schema |> select([s], json_extract_path(s.meta, ["a\\b"])) |> plan()
+    assert all(query) == ~S{SELECT json_extract(s0.`meta`, '$."a\\\\b"') FROM `schema` AS s0}
+
+    query = Schema |> select([s], json_extract_path(s.meta, ["a\\"])) |> plan()
+    assert all(query) == ~S{SELECT json_extract(s0.`meta`, '$."a\\\\"') FROM `schema` AS s0}
   end
 
   test "nested expressions" do