[英]Saving the order of associated records in a Rails has_many :through association
I'm working on a Rails plugin that includes a way to modify the order of associated records in a has_many :through association. 我正在开发一个Rails插件,该插件包括一种修改has_many:through关联中关联记录顺序的方法。 Say we have the following models:
假设我们有以下模型:
class Playlist < ActiveRecord::Base
has_many :playlists_songs, :dependent => :destroy
has_many :songs, :through => :playlists_songs
end
class Song < ActiveRecord::Base
has_many :playlists_songs, :dependent => :destroy
has_many :playlists, :through => :playlists_songs
end
class PlaylistsSong < ActiveRecord::Base
belongs_to :playlist
belongs_to :song
end
If we change the order of a Playlist's Songs (eg @playlist.songs.rotate!
), Rails doesn't touch the records in the playlists_songs table (I'm using Rails 3.1), which makes sense. 如果我们更改播放列表的歌曲的顺序(例如
@playlist.songs.rotate!
),Rails不会触摸playlists_songs表中的记录(我使用的是Rails 3.1),这很有意义。 I'd like to make any call to Playlist's songs= method save the order of the Songs, though, perhaps by either deleting the relevant existing rows in playlists_songs and creating new ones in the proper order (so that :order => "id"
could be used when retrieving them) or by adding a sort:integer column to playlists_songs and updating those values accordingly. 我想对Playlist的songs =方法进行任何调用,以保存Songs的顺序,也许是通过删除playlists_songs中现有的相关行并以适当的顺序创建新行(以便
:order => "id"
可以在检索它们时使用)或通过在playlists_songs中添加sort:integer列并相应地更新这些值。
I didn't see any callbacks (eg before_add) that would allow this. 我没有看到任何允许这样做的回调(例如before_add)。 In ActiveRecord::Associations::CollectionAssociation , the relevant methods seem to be writer , replace , and replace_records , but I'm lost on what the best next step would be.
在ActiveRecord :: Associations :: CollectionAssociation中 ,相关的方法似乎是writer , replace和replace_records ,但是我对下一步的最佳方法迷失了。 Is there a way to extend or safely override one of these methods to allow for the functionality I'm seeking (preferably for only specific associations), or is there a different, better approach for this?
有没有一种方法可以扩展或安全地覆盖这些方法中的一种,以允许我正在寻找的功能(最好仅针对特定的关联),或者是否有其他更好的方法呢?
Have you looked at acts_as_list ? 您看过act_as_list吗? It's one of the most old-school of rails plugins, and is intended to handle this sort of problem.
它是最古老的Rails插件之一,旨在解决此类问题。
Rather than sorting on id
, it sorts on a positional column. 而不是对
id
排序,而是对位置列进行排序。 Then it's simply a matter of updating the position, rather than the messy business of changing the id
or deleting/replacing records. 然后,仅需更新位置,而不是更改
id
或删除/替换记录的麻烦事务。
In your case, you'd simply add a position
integer column to PlayListSong
, then: 在您的情况下,您只需将
position
整数列添加到PlayListSong
,然后:
class PlayListSong
acts_as_list :scope => :play_list_id
end
As you point out in the comments, the methods in acts_as_list
work mostly on individual items in the list, and there's no "reorder" functionality out of the box. 正如您在注释中指出的那样,
acts_as_list
的方法主要对列表中的单个项目起作用,并且没有开箱即用的“重新排序”功能。 I would not recommend tampering with replace_records
to do this. 我不建议篡改
replace_records
来做到这一点。 It would be cleaner and more explicit to write a method making use of the same position column as the plugin. 编写一种使用与插件相同的position列的方法会更加简洁明了。 For example.
例如。
class PlayList
# It makes sense for these methods to be on the association. You might make it
# work for #songs instead (as in your question), but the join table is what's
# keeping the position.
has_many :play_list_songs, ... do
# I'm not sure what rotate! should do, so...
# This first method makes use of acts_as_list's functionality
#
# This should take the last song and move it to the first, incrementing
# the position of all other songs, effectively rotating the list forward
# by 1 song.
def rotate!
last.move_to_top unless empty?
end
# this, on the other hand, would reorder given an array of play_list_songs.
#
# Note: this is a rough (untested) idea and could/should be reworked for
# efficiency and safety.
def reorder!(reordered_songs)
position = 0
reordered_songs.each do |song|
position += 1
# Note: update_column is 3.1+, but I'm assuming you're using it, since
# that was the source you linked to in your question
find(song.id).update_column(:position, position)
end
end
end
end
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