（Ruby on Rails）帮助将哈希添加到数据库

Question

Ruby 2.0、Rails 4.1.0、sQlite3。我必须在 Hash 中创建参数以添加到我的数据库。我有 yaml 文件和模型：

class User < ActiveRecord::Base
  has_many :tweets
  accepts_nested_attributes_for :tweets
end
class Tweet < ActiveRecord::Base
  belongs_to :user
end

我有 15 个用户。尝试运行这段代码

UsTw_model_params = {user: []}

count_of_users = seeds_yml["users"].length - 1

for i in 0..count_of_users do 
  UsTw_model_params[:user][i] = {}
  UsTw_model_params[:user][i][:name] = seeds_yml["users"][i]["name"]
  UsTw_model_params[:user][i][:email] = seeds_yml["users"][i]["email"]
  UsTw_model_params[:user][i][:password] = seeds_yml["users"][i]["password"]
  UsTw_model_params[:user][i][:avatar] = seeds_yml["users"][i]["avatar"]
  UsTw_model_params[:user][i][:tweets_attributes] = []

  if seeds_yml["users"][i].has_key?(:tweets)
    count_of_tweets = seeds_yml["users"][i]["tweets"].length - 1
    for j in 0..count_of_tweets do
        UsTw_model_params[:user][i][:tweets_attributes][j] = {}
        UsTw_model_params[:user][i][:tweets_attributes][j][:post] = seeds_yml["users"][i]["tweets"][j]["post"]
        UsTw_model_params[:user][i][:tweets_attributes][j][:created_at] = seeds_yml["users"][i]["tweets"][j]["created_at"]
    end 
  end
end

User.create(UsTw_model_params[:user])

并得到错误ActiveRecord::UnknownAttributeError: unknown attribute: user

怎么了？

Answer 1

首先，在 Ruby 中以大写字母开头的任何内容都被视为常量。 重新分配常量会导致警告。 具体来说：

UsTw_model_params = {user: []} # is a constant!

例子：

class User
module Huggable
TAU = 2 * PI

变量应该by convention 在蛇形盒中，例如：

user_tweet_params

其次，您可以留下 for 循环。 Ruby 有更好的方法在数组和其他枚举中循环，例如 map、each 等。

# Loop though seeds_yml["users"] and create a new array
user_tweet_params = seeds_yml["users"].map do |user|
    # with_indifferent_access allows us to use symbols or strings as keys
    user = user.with_indifferent_access
    user.slice!(:name, :email, :password, :avatar, :tweets)

    # Does the user have tweets?
    # We use try(:any?) incase user["tweets"] is nil
    if user[:tweets].try(:any?)
        # Take the tweets and nest then under tweet_attributes
        user[:tweet_attributes] = user.tweets.map do |tweet|
            tweet.with_indifferent_access.slice!(:post, :created_at)
        end
    end

    # remove the original tweets
    user.delete(:tweets)
    # return user
    user
end