问题
Can't understand how Rails association with models works. Here is simple question:
There are two tables
products
id| name | status
1 | Tube | 0
2 | Pillar | 1
3 | Book | 0
4 | Gum | 1
5 | Tumbler | 2
statuses
status | name
0 | Unavailable
1 | In stock
2 | Discounted
With ~ same names for models and controllers.
I don't what to create new row in statuses table on every new product. And i want to show status name in erb. What should i write in models and in migration file (for example for which belong_to, has_one or has_many...)?
回答1:
Product should belongs_to :status and Status should has_many :products for a simple one-to-many association, and you aren't required to set a status for a product. In erb you'd use <%= @product.status.name %>. To set up those migrations, create_table :products do |t| t.string :name; t.integer :status_id; end and create_table :statuses do |t| t.string :name; end
more information here
回答2:
First of all for in accordance with rails conventions you need to rename product.status to product.status_id.
product belongs_to :status
status has_many :products
Product.find(1).status.name should be 'Unavailable'
回答3:
If you understand the basics of relational database then it's pretty much the same thing.
When you say, status belongs_to :product and product has_many :statuses, it essentially means status table has a foreign key which you can use to retrieve all status rows for a given product id.
To establish this relationship, you'll need to create a new column product_id in your statuses table:
rails g migration AddProductIdToStatuses product_id:integer
Once done, add the following in your product.rb:
has_many :statuses
and this in your status.rb:
belongs_to :product
来源：https://stackoverflow.com/questions/19409912/rails-association-with-models-and-migration