Add the ability for parameter values to accept a Proc

CHANGELOG.md

@@ -2,7 +2,7 @@ Next Release
 ============
 
 #### Features
-
+* [#558](https://github.com/intridea/grape/pull/558): Support lambda-based values for params - [@wpschallenger](https://github.com/wpschallenger)
 * [#510](https://github.com/intridea/grape/pull/510): Support lambda-based default values for params - [@myitcv](https://github.com/myitcv).
 * [#511](https://github.com/intridea/grape/pull/511): Added `required` option for OAuth2 middleware - [@bcm](https://github.com/bcm).
 * [#520](https://github.com/intridea/grape/pull/520): Use `default_error_status` to specify the default status code returned from `error!` - [@salimane](https://github.com/salimane).

README.md

@@ -378,6 +378,15 @@ params do
 end
 ```
 
+The :values option can also be supplied with a Proc to be evalutated at runtime, for example given a status
+model you may want to restrict by hashtags that you have previously defined in the HashTag model.
+
+```ruby
+params do
+  required :hashtag, type: String, values: -> { Hashtag.all.map{|ht| ht.tag} }
+end
+```
+
 Parameters can be nested using `group` or by calling `requires` or `optional` with a block.
 In the above example, this means `params[:media][:url]` is required along with `params[:id]`,
 and `params[:audio][:format]` is required only if `params[:audio]` is present.

lib/grape/validations.rb

@@ -191,6 +191,10 @@ def configure_declared_params
       def validates(attrs, validations)
         doc_attrs = { required: validations.keys.include?(:presence) }
 
+        values = validations[:values]
+        values = (values.is_a?(Proc) ? values.call : values)
+        validations[:values] = doc_attrs[:values] = values if values
+
         # special case (type = coerce)
         validations[:coerce] = validations.delete(:type) if validations.key?(:type)
 
@@ -212,7 +216,7 @@ def validates(attrs, validations)
         end
 
         # type should be compatible with values array, if both exist
-        if coerce_type && values && values.any? { |v| !v.instance_of?(coerce_type) }
+        if coerce_type && values && (values.is_a?(Proc) ? values.call : values).any? { |v| !v.instance_of?(coerce_type) }
           raise Grape::Exceptions::IncompatibleOptionValues.new(:type, coerce_type, :values, values)
         end
 

lib/grape/validations/values.rb

@@ -2,7 +2,7 @@ module Grape
   module Validations
     class ValuesValidator < Validator
       def initialize(attrs, options, required, scope)
-        @values = options
+        @values = (options.is_a?(Proc) ? options.call : options)
         @required = required
         super
       end

spec/grape/validations/values_spec.rb

@@ -20,6 +20,13 @@ class API < Grape::API
         get '/default/valid' do
           { type: params[:type] }
         end
+
+        params do
+          optional :type, values: -> { ['valid-type1', 'valid-type2', 'valid-type3'] }, default: 'valid-type2'
+        end
+        get '/lambda' do
+          { type: params[:type] }
+        end
       end
     end
   end
@@ -52,6 +59,18 @@ def app
     last_response.body.should eq({ type: "valid-type2" }.to_json)
   end
 
+  it 'allows a proc for values' do
+    get('/lambda', type: 'valid-type1')
+    last_response.status.should eq 200
+    last_response.body.should eq({ type: "valid-type1" }.to_json)
+  end
+
+  it 'does not allow an invalid value for a parameter using lambda' do
+    get("/lambda", type: 'invalid-type')
+    last_response.status.should eq 400
+    last_response.body.should eq({ error: "type does not have a valid value" }.to_json)
+  end
+
   it 'raises IncompatibleOptionValues on an invalid default value' do
     subject = Class.new(Grape::API)
     expect {