probably, all attributes must be set when request. I want only word to be the necessary parameter.

[hi-ogawa]

Started POST "/api/items" for 127.0.0.1 at 2015-08-28 00:53:13 +0900 Processing by Api::V1::ItemsController#create as JSON Parameters: {"category_id"=>"10", "item"=>{"word"=>"foo", "meaning"=>"ogogog", "picture"=>#<ActionDispatch::Http::UploadedFile:0x007fd553766648 @tempfile=#<Tempfile:/var/folders/zb/c8sq_fs51g10352jz8kwyl8c0000gn/T/RackMultipart20150828-77349-qmebhz>, @original_filename="Screen Shot 2015-04-19 at 13.47.57.png", @content_type="image/png", @headers="Content-Disposition: form-data; name=\"item[picture]\"; filename=\"Screen Shot 2015-04-19 at 13.47.57.png\"\r\nContent-Type: image/png\r\n">}} Can't verify CSRF token authenticity User Load (0.4ms) SELECT users.* FROM users WHERE users.auth_token = 'Nbj1VGzwMoKTyHBuFwwp' LIMIT 1 Category Load (0.4ms) SELECT categories.* FROM categories WHERE categories.user_id = 1 AND categories.id = 10 LIMIT 1 Command :: file -b --mime '/var/folders/zb/c8sq_fs51g10352jz8kwyl8c0000gn/T/9b474c56aa959b3626cffbb17630a2b320150828-77349-1h5709w.png' (0.2ms) BEGIN Command :: file -b --mime '/var/folders/zb/c8sq_fs51g10352jz8kwyl8c0000gn/T/9b474c56aa959b3626cffbb17630a2b320150828-77349-3gv41k.png' (0.2ms) ROLLBACK Completed 422 Unprocessable Entity in 1962ms (Views: 1.0ms | ActiveRecord: 1.2ms)

[hi-ogawa]

before_validation :default_values # this mustn't be before_save def default_values self.description ||= "" end