Styjun

I would like to return values in json that contain models to be associated using JBuilder.
But I don’t know how to do it. And I encounter the error that “undefined method xx”
Here is my setting of rails.

Model

app/models/item.rb

belongs_to :user

app/models/user.rb

include UserImageUploader[:image]
has_many :item

vim app/uploaders/user_image_uploader.rb

# MiniMagick
require 'image_processing/mini_magick'

class UserImageUploader < Shrine
 include ImageProcessing::MiniMagick
 # The determine_mime_type plugin allows you to determine and store the actual MIME type of the file analyzed from file content.
 plugin :determine_mime_type
 plugin :store_dimensions
 plugin :pretty_location
 plugin :processing
 plugin :recache
 #The versions plugin enables your uploader to deal with versions,
 #by allowing you to return a Hash of files when processing.
 plugin :versions

 process(:store) do |io, context|
 original = io.download

 thumbnail = ImageProcessing::MiniMagick
 .source(original)
 .resize_to_limit!(600, nil)

 original.close!

 original: io, thumbnail: thumbnail 
 end

 #plugin :versions

 #plugin :delete_promoted
 #plugin :delete_raw
end

items_controller.rb

@items = Item.includes(:user).page(params[:page] ||= 1).per(8).order('created_at DESC')
render 'index', formats: 'json', handlers: 'jbuilder'

Item/index.json.jbuilder

json.array! @items do |t|
 json.id t.id //get the value normally
 json.created_at t.created_at //get the value normally 
 Json.user_id t.user.id //undefined method `id’ 
 json.user_original_img t.user.image_url(:original) //undefined method `image_url' 
end

As above, I could not get the value of the model being associated.

By the way, I could check the value correctly with rails console.

Bundle exec rails c

Item.first.user.image_url(:original)

 Item Load (1.5ms) SELECT `items`.* FROM `items` ORDER BY `items`.`id` ASC LIMIT 1
 User Load (0.7ms) SELECT `users`.* FROM `users` WHERE `users`.`id` = 1 LIMIT 1
=> "https://xx.s3.ap-northeast-1.amazonaws.com/store/user/1/image/original-xx”

Item.first.user.id
 (19.0ms) SET NAMES utf8mb4, @@SESSION.sql_mode = CONCAT(CONCAT(@@sql_mode, ',STRICT_ALL_TABLES'), ',NO_AUTO_VALUE_ON_ZERO'), @@SESSION.sql_auto_is_null = 0, @@SESSION.wait_timeout = 2147483
 Item Load (0.9ms) SELECT `items`.* FROM `items` ORDER BY `items`.`id` ASC LIMIT 1
 User Load (0.8ms) SELECT `users`.* FROM `users` WHERE `users`.`id` = 1 LIMIT 1
=> 1

Let me know what points I am wrong with.

Thank you for reading my question.

It seems that some items in @items list, doesn't have associated user, or their user_id field is nil. Then item.user would be nil. When you do nil.image_url you get NoMethodError: undefined method 'image_url' for nil:NilClass .

You could add a foreign key constraint between Item and User in your migration, to avoid problems like this:

add_foreign_key :items, :users

NOTE:

Adding the foreign key would still allow empty values. You'd also have to add the following in your migration file to avoid empty values in user_id column:

change_column_null :items, :user_id, false

Thanks to @3limin4t0r for pointing this out.

app/models/user.rb

include UserImageUploader[:image]
has_many :item

should be has_many :items, not terribly confident on this, but this may be the reason you're finding blank columns in your db. A has_many, belongs_to relationship should default to required.