Ruby on Rails - 模型

模型创建

Model.new   # creates a new empty model
Model.create( :field ⇒ 'value', :other_field ⇒ 42 )
# creates an object with the passed parameters and saves it

Model.find_or_create_by_field( value )  
# searches for a record where "field = value", creates
# a new record if not found

User.find_or_create_by_name_and_email( 'ramjoe', '[email protected]')

模型关系

有四种关联模型的方法。has_one、has_many、belongs_to 和 has_and_belongs_to_many。假设有以下四个实体 -

def Order < ActiveRecord::Base
   has_many :line_items
   belongs_to :customer 
end

def LineItem < ActiveRecord::Base
   belongs_to :order
end

def Customer < ActiveRecord::Base
   has_many :orders
   has_one :address
end

def Address < ActiveRecord::Base
   belongs_to :customer
end

考虑以下关系 -

def Category < ActiveRecord::Base 
   has_and_belongs_to_many :products
end

def Product < ActiveRecord::Base
   has_and_belongs_to_many :categories  
end

关联联接模型

现在考虑以下关系。这说明了我们在定义关系时如何使用联接。

class Author < ActiveRecord::Base
   has_many :authorships
   has_many :books, :through ⇒ :authorships
end

class Authorship < ActiveRecord::Base
   belongs_to :author
   belongs_to :book
end

class Book < ActiveRecord::Base
   has_one :authorship
end

@author = Author.find :first
# selects all books that the author's authorships belong to.

@author.authorships.collect { |a| a.book }
selects all books by using the Authorship join model
@author.books 

检查 关联 以了解更多详情。