将数据库模型转换为模型 Ruby Rails

Question

我开始 Ruby Rails 通过学校的 purchase/resale 平台项目。当我尝试从我的关系模型转换它们时，我的模型出现问题。

首先，我对我的数据库进行了建模。这是简化的实体关系模型：

然后我将其翻译成关系模型：

最后，我在 Ruby Rails 上实现了它。

我实现了一个模型客户端：

class Client < ApplicationRecord
    attr_accessor :name

    validates :name, :presence => true

    has_many :purchasings, :dependent => :destroy

    has_many :sellers, :through => :purchasings
    has_many :articles, :through => :purchasings
end

我已经实现了一个模型卖家：

class Seller < ApplicationRecord
    attr_accessor :name

    validates :name, :presence => true

    has_many :purchasings, :dependent => :destroy

    has_many :sellers, :through => :purchasings
    has_many :articles, :through => :purchasings
end

我实现了一个模型文章

class Article < ApplicationRecord
    attr_accessor :quantity

    validates :quantity, :presence => true

    has_one :purchasing, :dependent => :destroy

    has_one :client, :through => :purchasings
    has_one :seller, :through => :purchasings
end

我已经实施了一个采购模型：

class Purchasing < ApplicationRecord
    attr_accessor :client_id, :seller_id, :article_id

    belongs_to :client, :class_name => "Client"
    belongs_to :seller, :class_name => "Seller"
    belongs_to :article, :class_name => "Article"

    validates :client_id, :presence => true
    validates :seller_id, :presence => true
    validates :article_id, :presence => true
end

我修改了采购数据库迁移：

class CreatePurchasing < ActiveRecord::Migration[5.1]
    def change
        [...]

        add_index :purchasings, :client_id
        add_index :purchasings, :seller_id
        add_index :purchasings, :article_id
        add_index :purchasings, [:client_id, :seller_id], :unique => true
    end

    def down
        [...]
    end
end

我知道这是不正确的，因为当我在 Rails 控制台上执行以下代码时：

cl1 = Client.create(:name => "John")
cl2 = Client.create(:name => "James")
sel1 = Seller.create(:nom => "Jack")
sel2 = Seller.create(:nom => "Jil")
a1 = Article.create(:quantity => 5)

p1 = Purchasing.new(:client => cl1, :client_id => cl1.id, :seller => sel1, :seller_id => sel1.id, :article => a1, :article_id => a1.id)
p1.save
p2 = Purchasing.new(:client => cl2, :client_id => cl2.id, :seller => sel1, :seller_id => sel1.id, :article => a1, :article_id => a1.id)
p2.save

p2.save returns 是的，而一件物品不能由同一卖家出售而由两个不同的客户购买。

Answer 1

您正在为采购的错误列添加索引 table。根据要求，article_id 和 seller_id 最好不要重复。所以你实际上需要的是 seller_id 和 article_id 列的唯一性约束。您可以通过在数据库层上的两列 seller_id 和文章 ID 的组合上创建唯一索引来实现。您还应该在购买模型上添加应用层验证。

class Purchasing < ApplicationRecord
attr_accessor :client_id, :seller_id, :article_id

belongs_to :client, :class_name => "Client"
belongs_to :seller, :class_name => "Seller"
belongs_to :article, :class_name => "Article"

validates :client_id, :presence => true
validates :seller_id, :presence => true
validates :article_id, :presence => true

validates :article_id, uniqueness: {scope: :seller_id}
end

现在你也应该写一个数据库迁移来为这两列添加唯一索引。

    class AddUniquenessConstraintInPurshasing < ActiveRecord::Migration
       def change
         add_index :purchasings, [:article_id, :seller_id], :unique => true
    end

结束

将数据库模型转换为模型 Ruby Rails

Translating Database Models to Models on Ruby On Rails

ruby-on-rails

ruby

database

entity-relationship

relational-model