通过关联作用域:加入和合并 [英] scope through associations : joins and merge

问题描述

我有三个模型:User、Product 和 Transaction.(Transaction属于两者，User有很多Product，Product有很多User, 通过 Transaction)

I have three models : User, Product and Transaction. (Transaction belongs_to both, and User has many Product and Product has many User, through Transaction)

在我的 Transaction 模型中，我有一个 current 交易的范围:

In my Transaction model, I have a scope for current transactions :

scope :current, -> { where 'transactions.start_date IS NOT NULL AND transactions.end_date IS NULL' }

我希望能够在控制台中执行此操作，以便检索具有 current 交易的所有产品:

I want to be able to do that in the console, in order to retrieve all the products that have a current transaction :

User.first.products.owned

在控制台中，我可以使用:

In the console, I can make it happen with :

User.first.products.merge(Transaction.current.ownership)

第一次尝试

所以我将它添加到我的 Product 模型中:

def self.owned
  merge(Transaction.current.ownership)
end

我在控制台输入:

User.first.products.owned

但是 Rails 控制台告诉我的是什么:

But here what's rails console tells me :

NoMethodError: undefined method `merge' for #<Class:0x00000004e2c0f8>
    from /home/flo/.rvm/gems/ruby-2.0.0-p195/gems/activerecord-4.0.0.rc1/lib/active_record/dynamic_matchers.rb:22:in `method_missing'

其他尝试

如果我将它添加到我的 Product 模型中:

def self.owned
  joins(:transactions).merge(Transaction.current.ownership)
end

我在控制台输入:

User.first.products.owned

但它检索当前交易的所有产品，而不仅仅是当前交易的第一个用户的产品.

But it retrieve all products with a current transaction, and not only the first user's products with a current transaction.

你知道我做错了什么吗?

Do you have any idea of what I'm doing wrong ?

推荐答案

因为您只是没有订购或限制您的产品.

Of cause you just didnt oder or limit your products.

scope :current, where('transactions.start_date IS NOT NULL AND transactions.end_date IS NULL').order("by whatever").limit(1)

您可能需要订购正确的产品，否则您可以删除订购方法.

You may need to order it the right product is selected if not you can remove the order method.

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