rails-param

Parameter Validation & Type Coercion for Rails

This is a port of the gem sinatra-param for the Rails framework. All the credits go to @mattt. It has all the features of the sinatra-param gem, I used bang methods (like param!) to indicate that they are destructive as they change the controller params object and may raise an exception.

REST conventions take the guesswork out of designing and consuming web APIs. Simply GET, POST, PATCH, or DELETE resource endpoints, and you get what you'd expect.

However, when it comes to figuring out what parameters are expected... well, all bets are off.

This Rails extension takes a first step to solving this problem on the developer side.

rails-param allows you to declare, validate, and transform endpoint parameters as you would in frameworks like ActiveModel or DataMapper.

Example

  # GET /search?q=example
  # GET /search?q=example&categories=news
  # GET /search?q=example&sort=created_at&order=ASC
  def search
    param! :q,           String, required: true
    param! :categories,  Array
    param! :sort,        String, default: "title"
    param! :order,       String, in: %w(asc desc), transform: :downcase, default: "asc"
    param! :price,       String, format: "[<\=>]\s*\$\d+"

    {...}
  end
end

Parameter Types

By declaring parameter types, incoming parameters will automatically be transformed into an object of that type. For instance, if a param is Boolean, values of '1', 'true', 't', 'yes', and 'y' will be automatically transformed into true.

String
Integer
Float
:boolean/TrueClass/FalseClass ("1/0", "true/false", "t/f", "yes/no", "y/n")
Array ("1,2,3,4,5")
Hash ("key1:value1,key2:value2")
Date, Time, & DateTime

Validations

Encapsulate business logic in a consistent way with validations. If a parameter does not satisfy a particular condition, an exception (RailsParam::Param::InvalidParameterError) is raised. You may use the rescue_from method in your controller to catch this kind of exception.

required
blank
is
in, within, range
min / max
format

Defaults and Transformations

Passing a default option will provide a default value for a parameter if none is passed. A default can defined as either a default or as a Proc:

param! :attribution, String, default: "©"
param! :year, Integer, default: lambda { Time.now.year }

Use the transform option to take even more of the business logic of parameter I/O out of your code. Anything that responds to to_proc (including Proc and symbols) will do.

param! :order, String, in: ["ASC", "DESC"], transform: :upcase, default: "ASC"
param! :offset, Integer, min: 0, transform: lambda {|n| n - (n % 10)}

Thank you

Many thanks to:

Contact

Nicolas Blanco

License

rails-param is available under the MIT license. See the LICENSE file for more info.