如果你希望能够根据特定的缺失参数返回一个错误，而不必切换所有参数:

required_params = [:one, :two, :three]
required_params.each do |param|
  if params.has_key?(param)
    render json: { errors: "Missing parameter #{param.to_s}." }, :status => :bad_request 
    return
  end
end

简单如馅饼:

if !params[:one].nil? and !params[:two].nil?
  #do something...
elsif !params[:one].nil?
  #do something else...
elsif !params[:two].nil?
  #do something extraordinary...
end

if params[:one] && params[:two]
 ... do something ...
elsif params[:one]
 ... do something ...
end

我刚在RubyInRails类上读到这个 http://api.rubyonrails.org/classes/Object.html#method-i-blank-3F

你可以用空白?方法，该方法等价于params[:one].nil?| | params[:]空虚吗?

(如)

if params[:one].blank? 
  # do something if not exist
else
  # do something if exist
end

if params[:one] && param[:two]
  ... excute code ..
end

你也可以使用params[:two].empty来检查参数是否为空

我是这么做的，

before_action :validate_presence

然后是以下几种方法:

    def check_presence
  params[:param1].present? && params[:param2].present?
 end

 def validate_presence
  if !check_presence
    render json:  {
                      error:  {
                                message: "Bad Request, parameters missing.",
                                status: 500
                              }
                    }
  end
 end