[英]Rails order a has_many relation using a through table
I have a User and a Campaign model in my rails app. 我的Rails应用程序中有一个用户和一个Campaign模型。 A campaign has_many
users and a user has_one
campaign. 一个广告系列有has_many
用户和一个用户has_one
广告系列。
I want to order the users in the campaign by the date that they were added to it. 我想在广告系列中的用户添加日期之前对其进行排序。
To do that, I created a through table called CampaignUser. 为此,我创建了一个名为CampaignUser的穿透表。 I thought that I'd be able to order by the created_at
column in that table, but I couldn't see an easy way to do it. 我以为可以通过该表中的created_at
列进行排序,但是我看不到一种简单的方法。 See the classes below: 请参阅以下课程:
class Campaign < ApplicationRecord
has_many :campaign_users
has_many :users, through: :campaign_users
end
class User < ApplicationRecord
has_one :campaign, through: :campaign_users, dependent: :destroy
end
class CampaignUser < ApplicationRecord
belongs_to :campaign
belongs_to :user
end
Ideally, I'd like to write a line like this in my Campaign class: 理想情况下,我想在Campaign类中编写如下代码:
has_many :users, through: campaign_users, -> { order(created_at: :desc) }
Where created_at
refers to campaign_users
and not to users
. 其中created_at
是指campaign_users
而不是users
。 Is there a way to do that? 有没有办法做到这一点?
I could just write a method on Campaign myself to order the users manually, but then I'd have to make sure I call that method everywhere instead. 我可以自己在Campaign上编写一个方法来手动订购用户,但随后必须确保在所有地方调用该方法。 It seems like there should be an easier way. 似乎应该有一个更简单的方法。
Edit: 编辑:
Adding a scope to the user, as suggested in other answers is more problematic in this case. 在其他情况下, 如其他答案中所建议的那样 ,向用户添加范围会更成问题。 I'm looking to order users by a property of the through table, not a property of the user itself. 我正在按贯通表的属性而不是用户本身的属性对用户排序。 Is there a way to write the following line, replacing email
with campaign_users.created_at
, or something similar? 有没有办法写下面的行,用campaign_users.created_at
或类似的东西代替email
?
has_many :users, -> { order(email: :desc) }, :through => :campaign_users
EDIT : Thanks to @AdColvin I changed the code block to make it work ;) 编辑:感谢@AdColvin,我更改了代码块以使其工作;)
Have you tried something like 你尝试过类似的东西吗
has_many :users, -> { order('campaign_users.created_at DESC') }, through: campaign_users
You can do that because ActiveRecord will generate a JOIN in the resulting SQL, then you can order on any table that is joined. 您可以这样做,因为ActiveRecord会在结果SQL中生成一个JOIN,因此您可以在任何已联接的表上进行排序。
Also, the campaign_users
in the order statement should be the name of the table, not the name of the model or the relation 另外,order语句中的campaign_users
应该是表的名称,而不是模型或关系的名称
The trick is as @kevcha has already pointed out calling order with a string of the column you want. 诀窍是因为@kevcha已经指出了带有所需列字符串的调用顺序。
But instead of adding the order clause directly to the association you may want to use a association extension : 但是,您可能不想使用关联扩展,而不是直接将order子句添加到关联中 :
class Campaign < ApplicationRecord
has_many :campaign_users
has_many :users, through: :campaign_users do
def order_by_join_date
order('campaign_users.created_at DESC')
end
end
end
This lets you call campaign.users.order_by_join_date
to explicitly get the records in a specific order. 这使您可以调用campaign.users.order_by_join_date
以明确地按特定顺序获取记录。 It avoids some of the same pitfalls that surround default scope . 它避免了默认范围周围的一些陷阱 。
@kevcha When I tried your answer exactly as you suggested, I got the following error: @kevcha当我完全按照您的建议尝试回答时,出现以下错误:
syntax error, unexpected '\\n', expecting => ...mpaign_users.created_at ASC') } 语法错误,意外的'\\ n',期望=> ... mpaign_users.created_at ASC')}
But, when I add the scope just after has_many :users
, it works fine: 但是,当我在has_many :users
之后添加范围时,它可以正常工作:
has_many :users, -> { order('campaign_users.created_at DESC') }, through: :campaign_users
Also worth noting is that created_at
seems to be identical for objects created from a fixture. 另外值得注意的是, created_at
对于从灯具创建的对象似乎是相同的。 I wasn't aware of that. 我没有意识到。 I had to explicitly set created_at in my fixtures for my tests around this to pass. 我必须在夹具中显式设置created_at,以便我的测试通过。
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