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

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

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

你可以这样写得更简洁:

required = [:one, :two, :three]
if required.all? {|k| params.has_key? k}
  # here you know params has all the keys defined in required array
else
  ...
end

这是针对同一个问题拼凑出来的:

before_filter :validate_params

private

def validate_params
  return head :bad_request unless params_present?
end

def params_present?  
  Set.new(%w(one two three)) <= (Set.new(params.keys)) &&
  params.values.all?
end

第一行使用<=子集?检查目标键是否存在于参数的键中。操作符。 Enumerable.all吗?如果任何值为nil或false，则返回false。