哈囉，大家好！

愉快的週末就要來做些廢廢的事情，如練習語法？

接續前兩日的研究，目前被翻爛的書知道了能用JSONPlaceholder來seeding sample data，也知道可選用適合的HTTP client parse JSON API，昨天也順利地seeding 了Post data。

今天則是想極致偷懶，讓seeding task 能自動根據attributes 去抓API response 相對的value，而前置作業是要先乖乖將各個Model 的attributes 定義好。根據Guide 下方列的資訊，目前有：
/posts/1/comments
/albums/1/photos
/users/1/albums
/users/1/todos
/users/1/posts

簡單畫一下其關聯圖：

好了後就開始來處理tables 的migration 囉：

  create_table "albums", force: :cascade do |t|
    t.string "userId"
    t.text "title"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  create_table "comments", force: :cascade do |t|
    t.integer "postId"
    t.string "name"
    t.text "email"
    t.text "body"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  create_table "photos", force: :cascade do |t|
    t.integer "albumId"
    t.text "title"
    t.text "url"
    t.text "thumbnailUrl"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  create_table "posts", force: :cascade do |t|
    t.integer "userId"
    t.text "title"
    t.text "body"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  create_table "todos", force: :cascade do |t|
    t.integer "userId"
    t.text "title"
    t.boolean "completed"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
  end

  create_table "users", force: :cascade do |t|
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.string "name"
    t.string "username"
    t.text "email"
    t.text "phone"
    t.text "website"
  end

接著我們一樣先建立一個task 來一步步修改：

# 根據昨天的經驗，我們能先寫出一個基本版：

# Seeding post
url = 'https://jsonplaceholder.typicode.com/posts'
post_data = HTTParty.get(url).parsed_response

post_data.each do |post|
  Post.create(userId: post["userId"], title: post["title"], body: post["body"])
end
puts "Seeding post completed"

# Seeding comment
url = 'https://jsonplaceholder.typicode.com/comments'
comment_data = HTTParty.get(url).parsed_response

comment_data.each do |post|
  Comment.create(postId: comment["postId"], name: comment["name"], email: comment["email"], body: comment["body"])
end
puts "Seeding comment completed"

但由以上的兩個blocks 來看，如果我們要seeding 這六個Model 的data，就會有六個類似的blocks，且每個欄位都需要手動輸入column name 和response key，這離懶人高尚的境界相去甚遠...

因此，我想先將需要的table name、Model name、url 尾綴整理一下：

models = [ 'post' ] # 之後會擴充加入其他Models

# 1. 先處理Model name 的轉換
models.map do |model_name|
  model_name = model_name.humanize # 能把首字大寫，但因為本身還是String，所以需要利用const_get 方法來轉換為Model name
  model_name.class
end

> String < Object  
 
models.map do |model_name|
  model_name = Class.const_get(model_name.humanize)
  model_name.class
end

> Class < Module

# 2. 再來處理url 的尾綴
url = "https://jsonplaceholder.typicode.com/#{model_name}s"
> "https://jsonplaceholder.typicode.com/posts"

接著我們要處理建立資料表時會自動帶入的欄位：[ "id", "created_at", "updated_at" ]
這裡可以用attributes.keys這方法來檢視：

models = [ 'post' ] # 懶人的最終目標是只想改這行 XD

models.map do |model_name|
  model_class_name = Class.const_get(model_name.humanize)
  model_attributes = model_class_name.new.attributes.keys
end

>>
        [0] "id",
        [1] "userId",
        [2] "title",
        [3] "body",
        [4] "created_at",
        [5] "updated_at"

# 來刪掉那些多餘的欄位
models = [ 'post' ]
models.map do |model_name|
  model_class_name = Class.const_get(model_name.humanize)
  model_attributes = model_class_name.new.attributes.keys - [ "id", "created_at", "updated_at" ]
end

>>
        [0] "userId",
        [1] "title",
        [2] "body"

再來則是要處理API response 內多餘的keys & values，如users 因帶有address、company 等我暫時沒用到的keys，也就是User.attributes 沒有，若整包當成Model.create 的params 則會噴錯。

先給大家看看沒處理時的狀況：

models = [ 'user' ]
models.map do |model_name|
  model_class_name = Class.const_get(model_name.humanize)
  model_attributes = model_class_name.new.attributes.keys - [ "id", "created_at", "updated_at" ]
  url = "https://jsonplaceholder.typicode.com/#{model_name}s"
  response = HTTParty.get(url).parsed_response

  response.each do |res|
    model_class_name.create(res) # 整個response 丟進去
  end
end

Traceback (most recent call last):
        5: from (irb):66
        4: from (irb):66:in `map'
        3: from (irb):72:in `block in irb_binding'
        2: from (irb):72:in `each'
        1: from (irb):73:in `block (2 levels) in irb_binding'
ActiveModel::UnknownAttributeError (unknown attribute 'address' for User.)

讓我們再度利用上面model_attributes 的attributes 吧！並搭配ruby Hash 去掉keys 的方法except：

except(*keys) public
Returns a hash that includes everything except given keys.

models = [ 'user' ]
models.map do |model_name|
  model_class_name = Class.const_get(model_name.humanize)
  model_attributes = model_class_name.new.attributes.keys - [ "id", "created_at", "updated_at" ]
  url = "https://jsonplaceholder.typicode.com/#{model_name}s"
  response = HTTParty.get(url).parsed_response

  response.each do |res|
    keys_to_delete = res.keys - model_attributes
    res = res.except(*keys_to_delete) # I'm here
    model_class_name.create(res)
  end
end

最後再加上fail 的驗證和puts seeding 的處理狀況，咱們就完成啦！

Apidock: const_get
Apidock: except(for hash)

# 偷懶完成品
models = [ 'post', 'comment', 'album', 'photo', 'todo', 'user' ]
models.map do |model_name|

  model_class_name = Class.const_get(model_name.humanize)
  model_attributes = model_class_name.new.attributes.keys - [ "id", "created_at", "updated_at" ]

  url = "https://jsonplaceholder.typicode.com/#{model_name}s"
  response = HTTParty.get(url).parsed_response

  response.each do |res|
    keys_to_delete = res.keys - model_attributes
    res = res.except(*keys_to_delete)
    model_class_name.create(res)
  end

  fail unless model_class_name.count == response.count

  puts "Seeding #{model_name}s completed."
end

有沒有很懶呢？XD 希望大家都能成為怕麻煩的極致懶人~~！