Rails：以一对多关联访问其他对象

如何解决Rails：以一对多关联访问其他对象

这是我的代码：

class Recipe < ActiveRecord::Base
    has_many :neededingredients
end

class Neededingredient < ActiveRecord::Base
    belongs_to :ingredients
    belongs_to :recipes
end

class Ingredient < ActiveRecord::Base
    has_many :neededingredients
end

这是我的迁移：

create_table :recipes do |recipes|
    recipes.string :name,null: false
    recipes.string :indications,null: false
end

create_table :ingredients do |ingredients|
    ingredients.string :ingredient,null: false,uniqueness: true
end

create_table :neededingredients do |neededingredients|
    neededingredients.integer :quantity,null: false
    neededingredients.string :unit
    neededingredients.references :ingredients,foreign_key: true
    neededingredients.references :recipes,foreign_key: true
end

因此，配方具有多个NeededIngredients。 NeededIngredient引用了成分，并具有数量和单位（例如克）。我希望能够执行类似a_recipe.neededingredients的操作来找到给定配方的所有必需成分，或者进行a_needed_ingredient.recipe来获得给定的所需成分的配方。出于某种原因，我找不到执行此操作的方法。我的迁移或模型有什么问题吗？感谢您的帮助！

解决方法

这里问题的关键是命名/复数很差。我强烈建议您根据the Ruby conventions重命名此名称，以免造成混淆和将来的错误。

类名称应为CamelCase-NeededIngredient。做单独的复合词！

属性，表名，实例变量，路由，方法名以及其他所有内容都应为snake_case-needed_ingredient或needed_ingredients，具体取决于上下文。

这比insanelylongthingwitteninlowercase更容易阅读和理解。

将三个不同的表定义填充到一个迁移中（如果您正在这样做）是个坏主意。尤其是由于它不容易通过模型生成器生成迁移。进行单独的迁移后，您可以依次运行它们，然后分别回滚以使其正确进行。

class CreateNeededIngredients < ActiveRecord::Migration[6.0]
  def change
    # there is no need to use super long block argument names
    create_table :needed_ingredients do |t|
      t.decimal :quantity,null: false # yeah decimal
      t.string :unit
      t.references :ingredient,foreign_key: true # this should be singular!
      t.references :recipe,foreign_key: true # this should be singular!
      t.timestamps
    end
    # consider adding a unique index to avoid duplicates
    # add_index: :needed_ingredients,[:ingredient_id,:recipe_id],unique: true
  end
end

并不是说references的参数应该是单数，因为它是外键的名称。 Rails将通过变形来推导目标表。

然后，您需要设置has_many through: association才能将食谱和食材绑在一起：

class Recipe < ActiveRecord::Base
  has_many :needed_ingredients
  has_many :ingredients,through: :needed_ingredients
end

class NeededIngredient
  belongs_to :recipe # belongs_to is always singular!
  belongs_to :ingredient # belongs_to is always singular!
end

class Ingredient < ActiveRecord::Base
  has_many :needed_ingredients
  has_many :recipies,through: :needed_ingredients
end

这不是一对多的关联。它的多对多。如果需要显示配方的成分，则应注意，应遍历needed_ingredients关联而不是成分。

class NeededIngredient
  belongs_to :recipe # belongs_to is always singular!
  belongs_to :ingredient # belongs_to is always singular!

  # use delegation/proxing to avoid Law of Demeter violations
  def name
    ingredient.ingredient # why isn't this column just called name?
  end
end

class RecipiesController < ApplicationController
  def show
    @recipe = Recipe.include(:ingedients).find(params[:id])
  end 
end

# app/views/recipies/show.html.erb
<h1><%= @recipe.name %></h1>

<table>
  <thead>
    <tr>
      <th>Name</th>
      <th>Quantity</th> 
    </tr>
  </thead>
  <tbody>
  <% @recipe.needed_ingredients.each do |i|%>
    <tr>
      <td><%= i.name %></td>
      <td><%= i.quantity %> <%= i.unit %></td>  
    </tr>
  <% end %>
  </tbody>
</table>

,

在迁移和模型中，您使用复数而不是单数，并且应该使用has_many :through association

更改以下内容：

class Recipe < ApplicationRecord
  has_many :neededingredients
  has_many :ingredients,through: :neededingredients
end

class Neededingredient < ApplicationRecord
    belongs_to :ingredient
    belongs_to :recipe
end

class Ingredient < ApplicationRecord
    has_many :neededingredients
    has_many :recipes,through: :neededingredients
end

create_table :neededingredients do |neededingredients|
    neededingredients.integer :quantity,null: false
    neededingredients.string :unit
    neededingredients.references :ingredient,foreign_key: true
    neededingredients.references :recipe,foreign_key: true
end

现在您可以致电（例如）：Recipe.first.ingredients，Recipe.first.neededingredients，Ingredient.first.recipes