Rails 5常数，模型和虚拟属性

Question

我试图在Model虚拟属性中使用预定义常量。

当我创建用户时，它显示绝对的avatar_url并正常工作。

问题：

当我在登录方法中找到用户时，它仅返回相对url即"avatar_url": "/avatars/original/missing.png" ，这意味着#{SERVER_BASE_PATH}目前尚未插值。

它也可以与某些api调用一起正常工作，例如在更新用户时。 但并非在所有情况下都如此。 请帮助我如何解决此问题，以便在所有api调用中获取绝对网址

例：

模型：

class User < ApplicationRecord
    # user model
    # if avatar url is empty then use default image url
    # SERVER_BASE_PATH is defined in config/initializer/constant.rb
    attribute :avatar_url, :string, default: -> { "#{SERVER_BASE_PATH}/avatars/original/missing.png" }
end

控制器：

它具有简单的登录方法

class UsersController < ApplicationController
    def login
        response = OK()
        unless params[:email].present? and params[:password].present?
            render json: missing_params_specific('either user [email] or [password]') and return
        end
        response[:user] = []
        response[:status] = '0'

        begin
        user = User.find_by(email: params[:email].downcase)
        if user && user.authenticate(params[:password])
            # following line first check if user profile image exist then it places that image url given by paperclip
            # if not exist then url defined in model virtual attributes is used.
            user.avatar_url = user.avatar.url if user.avatar.url.present?
            user.set_last_sign_in_at user.sign_in_count
          response[:user] = user
          response[:status] = '1'
        else
          response[:message] = 'Invalid email/password combination' # Not quite right!
        end
        rescue => e
            response[:message] = e.message
        end
        render json: response and return
    end
end

API JSON响应：

{
  "JSON_KEY_STATUS_CODE": 1,
  "JSON_KEY_STATUS_MESSAGE": "OK",
  "server_time": 1490623384,
  "user": {
    "confirmed": true,
    "user_status": "Active",
    "admin": false,
    "user_role": "Standard",
    "first_name": "Super",
    "last_name": "User",
    "full_name": "Super User",
    "avatar_url": "/avatars/original/missing.png",  <-- Here (not absolute url)
    "is_active": true,
  },
  "status": "1"
}

Answer 1

据我了解，JSON响应上的"avatar_url"属性是您在将Paperclip与以下模型集成的模型上定义的default_url ：

class User < ActiveRecord::Base
  has_attached_file :avatar, 
                    styles: { medium: "300x300>", thumb: "100x100>" },
                    default_url: "/images/:style/missing.png"
  validates_attachment_content_type :avatar, content_type: /\Aimage\/.*\z/
end

您是否尝试使用SERVER_BASE_PATH设置default_url ？