[英]How do I order by foreign attribute for belongs_to reference where there are 2 keys to foreign table
我有一个Model,它与另一个Model有belongs_to
关联,如下所示
class Article
belongs_to :author, :class_name => "User"
end
如果我想找到作者订购的特定类型的所有文章,我会做类似以下的事情
articles = Article.all(:includes => [:author], :order => "users.name")
但是,如果Article
恰好有两个对User
引用,我该如何排序:author
?
class Article
belongs_to :editor, :class_name => "User"
belongs_to :author, :class_name => "User"
end
我试过了
articles = Article.all(:includes => [:author], :order => "users.name")
#=> incorrect results
articles = Article.all(:includes => [:author], :order => "authors.name")
#=> Exception Thrown
半解决方案如下。 这并不是很明显,但看着我的日志,我想出来了。
class Article
belongs_to :editor, :class_name => "User"
belongs_to :author, :class_name => "User"
end
基本上你需要做以下事情
articles = Article.all(:include => [:editor,:author], :order => 'articles_authors.name')
articles = Article.all(:include => [:editor,:author], :order => 'authors_articles.name')
这是我错过的别名的命名(articles_authors)
这个问题是,虽然看起来应该如下,但以下方法不起作用。
articles = Article.all(:include => [:editor,:author], :order => 'authors_articles.name')
articles = Article.all(:include => [:editor,:author], :order => 'editors_articles.name')
如果您有UI表并希望将订单字段发送到控制器,则可能会出现问题。 所以你可能想先在作者和编辑上订购。 但是对于其中一个查询会失败(除非您动态更改包含)
所以我想我已经钉了它。 这并不是很明显,但看着我的日志,我想出来了。
class Article
belongs_to :editor, :class_name => "User"
belongs_to :author, :class_name => "User"
end
基本上你需要做以下事情
articles = Article.all(:include => [:editor,:author], :order => 'articles_authors.name')
articles = Article.all(:include => [:editor,:author], :order => 'authors_articles.name')
这是我错过的别名的命名(articles_authors)
这在ActiveRecord中称为表别名。 当find
方法多次连接同一个表时,表的别名确定如下:
Active Record uses table aliasing in the case that a table is referenced
multiple times in a join. If a table is referenced only once, the standard table
name is used. The second time, the table is aliased as
#{reflection_name}_#{parent_table_name}. Indexes are appended for any more
successive uses of the table name.
有关更多详细信息,请参阅ActiveRecord 文档 。 搜索Table Aliasing
以导航到特定部分。
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