如何通过关系显示has_many中的唯一记录？ [英] How to display unique records from a has_many through relationship?

问题描述

我想知道通过Rails3中的关系显示has_many中唯一记录的最佳方法是什么。

I'm wondering what is the best way to display unique records from a has_many, through relationship in Rails3.

我有三种模型：

class User < ActiveRecord::Base
    has_many :orders
    has_many :products, :through => :orders
end

class Products < ActiveRecord::Base
    has_many :orders
    has_many :users, :through => :orders
end

class Order < ActiveRecord::Base
    belongs_to :user, :counter_cache => true 
    belongs_to :product, :counter_cache => true 
end

说我想列出客户订购的所有产品显示页面。

Lets say I want to list all the products a customer has ordered on their show page.

他们可能已经多次订购某些产品，所以我使用counter_cache根据订单数以降序显示。

They may have ordered some products multiple times, so I'm using counter_cache to display in descending rank order, based on the number of orders.

但是，如果他们多次订购产品，我需要确保每个产品仅列出一次。

But, if they have ordered a product multiple times, I need to ensure that each product is only listed once.

@products = @user.products.ranked(:limit => 10).uniq!

在有多个订单记录的情况下有效，但如果仅购买了一个产品，则会产生错误订购一次。 （排名是在其他位置定义的自定义排序功能）

works when there are multiple order records for a product, but generates an error if a product has only been ordered once. (ranked is custom sort function defined elsewhere)

另一种替代方法是：

@products = @user.products.ranked(:limit => 10, :select => "DISTINCT(ID)")

我不确定在这里采用正确的方法。

I'm not confident that I'm on the right approach here.

还有其他人解决吗？您遇到了什么问题？在哪里可以找到有关.unique之间差异的更多信息！和DISTINCT（）？

Has anyone else tackled this? What issues did you come up against? Where can I find out more about the difference between .unique! and DISTINCT()?

通过has_many通过关系生成唯一记录列表的最佳方法是什么？

What is the best way to generate a list of unique records through a has_many, through relationship?

谢谢

推荐答案

您是否尝试在has_many关联上指定：uniq选项：

Have you tried to specify the :uniq option on the has_many association:

has_many :products, :through => :orders, :uniq => true

来自 Rails文档：

：uniq

如果为true，则将从集合中省略重复项。与：through一起使用。

If true, duplicates will be omitted from the collection. Useful in conjunction with :through.

更新铁路4：

在Rails 4中， has_many：products，：through => ：orders，：uniq => true 已弃用。相反，您现在应该编写 has_many：products，->。 {独特}，通过：：orders 。请参阅 distinct部分，以获取has_many :: ActiveRecordAssociations文档上的关系以获取更多信息。感谢Kurt Mueller在他的评论中指出了这一点。

In Rails 4, has_many :products, :through => :orders, :uniq => true is deprecated. Instead, you should now write has_many :products, -> { distinct }, through: :orders. See the distinct section for has_many: :through relationships on the ActiveRecord Associations documentation for more information. Thanks to Kurt Mueller for pointing this out in his comment.

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