Support allow nil in length validator

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 #### Features
 
+* [#2464](https://github.com/ruby-grape/grape/pull/2464): Support allow `nil` in `length` validator - [@OuYangJinTing](https://github.com/OuYangJinTing).
 * Your contribution here.
 
 #### Fixes

README.md

@@ -1714,12 +1714,13 @@ end
 
 Parameters with types that support `#length` method can be restricted to have a specific length with the `:length` option.
 
-The validator accepts `:min` or `:max` or both options to validate that the value of the parameter is within the given limits.
+The validator accepts `:min` or `:max` or both options to validate that the value of the parameter is within the given limits,
+In addition, if need to allow `nil` value, must to pass the `allow_nil: true` option.
 
 ```ruby
 params do
   requires :str, type: String, length: { min: 3 }
-  requires :list, type: [Integer], length: { min: 3, max: 5 }
+  requires :list, type: [Integer], length: { min: 3, max: 5, allow_nil: true }
   requires :hash, type: Hash, length: { max: 5 }
 end
 ```

lib/grape/locale/en.yml

@@ -7,6 +7,7 @@ en:
         presence: 'is missing'
         regexp: 'is invalid'
         blank: 'is empty'
+        nil: 'is nil'
         values: 'does not have a valid value'
         except_values: 'has a value not allowed'
         same_as: 'is not the same as %{parameter}'

lib/grape/validations/validators/length_validator.rb

@@ -7,6 +7,7 @@ class LengthValidator < Base
         def initialize(attrs, options, required, scope, **opts)
           @min = options[:min]
           @max = options[:max]
+          @allow_nil = options[:allow_nil]
 
           super
 
@@ -18,6 +19,12 @@ def initialize(attrs, options, required, scope, **opts)
         def validate_param!(attr_name, params)
           param = params[attr_name]
 
+          if param.nil?
+            return if @allow_nil
+
+            raise Grape::Exceptions::Validation.new(params: [@scope.full_name(attr_name)], message: message(:nil))
+          end
+
           raise ArgumentError, "parameter #{param} does not support #length" unless param.respond_to?(:length)
 
           return unless (!@min.nil? && param.length < @min) || (!@max.nil? && param.length > @max)

spec/grape/validations/validators/length_spec.rb

@@ -81,6 +81,18 @@
       post 'zero_max' do
       end
 
+      params do
+        requires :list, type: [Integer], length: { min: 0, allow_nil: true }
+      end
+      post 'allow_nil_param' do
+      end
+
+      params do
+        requires :list, type: [Integer], length: { min: 0, allow_nil: false }
+      end
+      post 'disallow_nil_param' do
+      end
+
       params do
         requires :list, type: [Integer], length: { min: 2, message: 'not match' }
       end
@@ -187,6 +199,23 @@
     end
   end
 
+  describe 'when a nil value is passed' do
+    context '/allow_nil_param' do
+      it do
+        post '/allow_nil_param', list: nil
+        expect(last_response.status).to eq(201)
+      end
+    end
+
+    context '/disallow_nil_param' do
+      it do
+        post '/disallow_nil_param', list: nil
+        expect(last_response.status).to eq(400)
+        expect(last_response.body).to eq('list is nil')
+      end
+    end
+  end
+
   describe '/type_is_not_array' do
     context 'raises an error' do
       it do