代码之家 › 专栏 › 技术社区 › Thierry Lam

在rails中,如何向同一个模型添加多个外键?我有相当于Django的

django ruby-on-rails

Thierry Lam · 技术社区 · 14 年前

我使用的是rails 3 beta,我假设它的语法与2.x相似,我也不太熟悉ruby和rails。

在django中,同一模型的多个外键如下所示:

class Dish(models.Model):
    name = models.CharField(max_length=100)
    lunch = models.ForeignKey(Ingredient, related_name='lunch')
    dinner = models.ForeignKey(Ingredient, related_name='dinner')

class Ingredient(models.Model):
    spices = models.IntegerField()
    veggies = models.IntegerField()

在rails中,我考虑做如下事情:

# Migration file
create_table :dishes do |t|
  t.column :name, :string
end

create_table :ingredients do |t|
  t.column :spice, :integer
  t.column :veggies, :integer
  t.column: :dish_id, :integer
  t.column: :meal, :string  # lunch or dinner
end

# Models
class Dish < ActiveRecord::Base
  def lunch
    return # ingredient for the current dish where type == lunch
  end

  def dinner
    return # ingredient for the current dish where type == dinner
  end
end

上面的想法是正确的还是有更好的方法?

更多澄清: 这家餐厅在午餐和晚餐期间供应同一道菜,但在这两餐之间使用的配料量不同。每道菜最多可包含一个午餐配料对象和一个晚餐配料对象。

2 回复 | 直到 14 年前

klew 14 年前

首先,对我来说,如果使用string列只存储两种类型的内容,这看起来不太好。当有更多类型的食物时,可以将其存储为布尔值或整数。您可以添加一个数组,该数组将膳食类型id映射到 lunch 或 dinner 或者别的什么。

# Ingredient model
belongs_to :dish

def meal
  MEAL_TYPES[meal_id]
end

private
MEAL_TYPES = ['lunch', 'dinner']


# Dish model
has_one :lunch, :class_name => 'Ingredient', :conditions => {:meal_id => 0}
has_one :dinner, :class_name => 'Ingredient', :conditions => {:meal_id => 1}

然后在代码中,您可以将其用作休耕地:

@dish = Dish.find(params[:id])
@dish.lunch # returns lunch ingredients
@dish.dinner # returns dinner ingredients

@dish.lunch.meal # => "lunch"

Harish Shetty 14 年前

你的模型不清楚 1-to-1 或 1-to-n 之间的关系 Dish 模型及 Ingredients 模型。如果关系是 1对1 ,以下代码应有效:

class Dish < ActiveRecord::Base
 has_one :lunch, :class_name => 'Ingredient', :conditions => {:meal => 'lunch'}
 has_one :dinnner, :class_name => 'Ingredient', :conditions => {:meal => 'dinner'}

end
# now you can get lunch and dinner using the calls below on a Dish object.
dish.lunch
dish.lunch

如果关系是 1-N ,以下代码应有效:

class Dish < ActiveRecord::Base
 has_many :lunches, :class_name => 'Ingredient', :conditions => {:meal => 'lunch'}
 has_many :dinnners, :class_name => 'Ingredient', :conditions => {:meal => 'dinner'}
end