您的 total_on 方法返回的是关联，而不是数字.

Your total_on method is returning an association, not a number.

尝试附加 .count:

def total_on(date)
  calls.where("placed_at >= ? AND placed_at <= ?", date.beginning_of_day, date.end_of_day).count
end

你也可以给它一个日期范围来稍微缩短这个方法(实际上是一样的，但更容易阅读):

You can also give it a date range to shorten the method a bit (effectively the same, but easier to read):

def total_on(date)
  calls.where(placed_at: date.beginning_of_day..date.end_of_day).count
end

更新:

原始的placed_at"查询是否有效，还是因为NoMethodError而从未真正调用过?

Did the original "placed_at" query ever work, or was it never actually called because of the NoMethodError?

您的模型中似乎没有 placed_at 列，但我假设您也可以使用 created_at.

It doesn't look like there is a placed_at column in your model, but I assume you can used created_at just as well.

如果你想使用placed_at，你可以定义这个方法(为了样式我把名字改成了placed_on):

If you want to used placed_at, you could define this method (I changed the name to placed_on for style):

class Call < ActiveRecord::Base

  def self.placed_on(date)
    where(created_at: date.beginning_of_day..date.end_of_day)
  end

end

您可以将其链接到您的 total_on 方法中:

You can chain this into your total_on method:

class Phone < ActiveRecord::Base

  def total_on(date)
    calls.placed_on(date).count
  end

end