I have a Model which has a belongs_to
association with another Model as follows
class Article
belongs_to :author, :class_name => "User"
end
If I wanted to find all articles for a particular genre ordered by author I would do something like the following
articles = Article.all(:includes => [:author], :order => "users.name")
However if Article
happens to have two references to User
how can I sort on :author
?
class Article
belongs_to :editor, :class_name => "User"
belongs_to :author, :class_name => "User"
end
I have tried
articles = Article.all(:includes => [:author], :order => "users.name")
#=> incorrect results
articles = Article.all(:includes => [:author], :order => "authors.name")
#=> Exception Thrown
A half solution is as follows. It was not totally obvious but looking at my logs I figured it out.
class Article
belongs_to :editor, :class_name => "User"
belongs_to :author, :class_name => "User"
end
Basically you need to do the following
articles = Article.all(:include => [:editor,:author], :order => 'articles_authors.name')
articles = Article.all(:include => [:editor,:author], :order => 'authors_articles.name')
It is the naming of the alias that I missed (articles_authors)
The issue with this is that the following does not work although it seems like it should.
articles = Article.all(:include => [:editor,:author], :order => 'authors_articles.name')
articles = Article.all(:include => [:editor,:author], :order => 'editors_articles.name')
This may be an issue if you have a UI table and want to send the order field to the controller. So you may want to first order on author then editor. But it would fail for for one of the queries (unless you dynamically change the include too)
So I think I have nailed it. It was not totally obvious but looking at my logs I figured it out.
class Article
belongs_to :editor, :class_name => "User"
belongs_to :author, :class_name => "User"
end
Basically you need to do the following
articles = Article.all(:include => [:editor,:author], :order => 'articles_authors.name')
articles = Article.all(:include => [:editor,:author], :order => 'authors_articles.name')
It is the naming of the alias that I missed (articles_authors)
This is called Table Aliasing in ActiveRecord. When the find
method joins the same table more than once the alias names for the table is determined as follows:
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.
Refer to the ActiveRecord documentation for more details. Search for Table Aliasing
to navigate to the specific section.
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