#has_one

どうも！TAKUYAです！

今回は私もいまだに頭の中ごちゃごちゃしているRailsにおけるActive Recordのアソシエーション（model間の関連付け）についてまとめたものを記事としてあげておこうと思います。

アソシエーションとは

テーブル間のリレーションシップをモデルの上の関係として操作できるようにする仕組み。 アソシエーションを利用すると複数のテーブルにまたがるデータ操作もより直感的に利用することができる。

アソシエーションの種類

Railsでサポートされているアソシエーションは以下の6種類。

belongs_to

has_one

has_many

has_many :through

has_one :through

has_and_belongs_to_many

belongs_to

belongs_to関連付けを行なうと、他のモデルとの間に「1対1」のつながりを設定す…

Khi bạn làm việc với Polymorphic, bạn thường bắt đầu từ các ví dụ có sẵn trên internet mà hầu hết đều sử dụng has_many association. Điểm đặc biệt khi sử dụng has_many association là việc tương đối dễ dàng khởi tạo lồng cấp như sau:

@products.pictures.create( ... )

Nhưng đối với has_one association, nếu bạn sử dụng cú pháp trên thì ngay lập tức sẽ nhận được câu chửi từ máy tính, đại loại là hàm create không có đâu em yêu. Bạn sẽ rơi vào bế tắc sau khi tra đi tra lại và so sánh sample với project của mình xem có sai gì không, lục lọi mày mò đủ kiểu để cuối cùng phí rất nhiều thời gian (như tôi)

Trong trường hợp này, ta sử dụng cú pháp như sau:

Picture.create( :imageable => Product.create( ... ) )

---- 

Cách sử dụng cho trường hợp này:

@a = YObject.find(1) @a.reference

hoặc

I love having the ability to easily create/update multiple objects with a single form. There are some nice railscasts by Ryan Bates that describe how to do this in Ruby on Rails. What I needed was a way to make writing the attribute accessor methods easier. I also decided that there just weren’t enough rails plugins out there … so off to kill two birds with one stone.

The Plugin

The plugin is called association-attributes and it can be found on github. The goal was to make the process more semantic and most of all DRY. I decided that since we already had to have a method on the model to handle the association we would pattern after that. So, the two methods available are has_one_attr & has_many_attr.

The Model

So for a practical example of what this looks like in your model we will use a persons contact info. We also have a plugin out there that makes contact info easier since that is such a standard need and there is no reason to rewrite that all the time.

class Person < ActiveRecord::Base has_one :address, :as => :addressable, :dependent => :destroy has_one_attr :address has_many :phone_numbers, :as => :phoneable, :dependent => :destroy has_many_attr :phone_numbers end

What that does is creates the methods address_attributes & phone_number_attributes on Person so that we can use them in our form. These newly created methods handle creating & updating existing entries for addresses and phone numbers.

The View

We use HAML for all of our views so these examples are no exception.

- fields_for("person[phone_numbers_attributes][]", @person.phone_numbers.new) do |phf| %label{:for => "number"} Phone Number: = phf.hidden_field :id = phf.text_field :number

A few things to note from this example are:

The fields_for has an extra [] on the first parameter … this is because we have a has_many and that tells the browser to treat that as part of an array so that we can have more than one of that same name and it will get put into the array.

We are only doing a new item but you would use the same technique to display existing items by replacing @person.phone_numbers.new with a variable of the actual phone number.

We have an id hidden field … this is if we use an existing phone number object it will update rather than creating a new object. (it still works without that but deletes the old number and creates a new one)

- fields_for("person[address_attributes]", @person.build_address) do |af| %p %label{:for => "line_1"} Street Address: = af.text_field :line_1 %p %label{:for => "city"} City: = af.text_field :city %p %label{:for => "state"} State: = af.select :state, Address::VALID_STATES.map{|s| [s,s]}.sort %p %label{:for => "zip"} Zip: = af.text_field :zip

In future versions I will have a helper method that writes the fields_for for you as well. Looping through current objects and having an option to put a blank one at the end.

The Result