Ruby PG Gem：无法确定参数$ 1的数据类型

Question

我试图定义一个方法，该方法接受一个表示表名的可选参数，并将其传递给该方法中的SQL语句。当我在程序中运行代码时，我收到一条错误，说“＃34;无法确定参数$ 1的数据类型。”＃34;造成这种情况的原因是什么？如何解决？

这是我的代码。

def get_all_movies(order='title')
  sql = %{
    SELECT movies.title AS title, movies.year AS year, movies.rating AS rating,
    genres.name AS genre, studios.name AS studio
    FROM movies
    JOIN genres ON movies.genre_id = genres.id
    JOIN studios ON movies.studio_id = studios.id
    ORDER BY movies.#{order};
  }

  db_connection do |conn|
    order = conn.quote_ident(order)
    @results = conn.exec_params(sql, [order]).to_a
  end

  @get_all_movies = true
end

提前致谢！

编辑：这是工作代码：

def get_all_movies(order='title')
  sql = %{
    SELECT movies.title AS title, movies.year AS year, movies.rating AS rating,
    genres.name AS genre, studios.name AS studio
    FROM movies
    JOIN genres ON movies.genre_id = genres.id
    JOIN studios ON movies.studio_id = studios.id
    ORDER BY movies.#{order};
  }

  db_connection do |conn|
    order = conn.quote_ident(order)
    @results = conn.exec(sql).to_a
  end

  @get_all_movies = true
end