I want to be able to use two columns on one table to define a relationship. So using a task app as an example.
Attempt 1:
class User < ActiveRecord::Base
has_many :tasks
end
class Task < ActiveRecord::Base
belongs_to :owner, class_name: "User", foreign_key: "owner_id"
belongs_to :assignee, class_name: "User", foreign_key: "assignee_id"
end
So then Task.create(owner_id:1, assignee_id: 2)
This allows me to perform Task.first.owner
which returns user one and Task.first.assignee
which returns user two but User.first.task
returns nothing. Which is because task doesn't belong to a user, they belong to owner and assignee. So,
Attempt 2:
class User < ActiveRecord::Base
has_many :tasks, foreign_key: [:owner_id, :assignee_id]
end
class Task < ActiveRecord::Base
belongs_to :user
end
That just fails altogether as two foreign keys don't seem to be supported.
So what I want is to be able to say User.tasks
and get both the users owned and assigned tasks.
Basically somehow build a relationship that would equal a query of Task.where(owner_id || assignee_id == 1)
Is that possible?
I'm not looking to use finder_sql
, but this issue's unaccepted answer looks to be close to what I want: Rails - Multiple Index Key Association
So this method would look like this,
Attempt 3:
class Task < ActiveRecord::Base
def self.by_person(person)
where("assignee_id => :person_id OR owner_id => :person_id", :person_id => person.id
end
end
class Person < ActiveRecord::Base
def tasks
Task.by_person(self)
end
end
Though I can get it to work in Rails 4
, I keep getting the following error:
ActiveRecord::PreparedStatementInvalid: missing value for :owner_id in :donor_id => :person_id OR assignee_id => :person_id
class User < ActiveRecord::Base
def tasks
Task.where("owner_id = ? OR assigneed_id = ?", self.id, self.id)
end
end
Remove has_many :tasks
in User
class.
Using has_many :tasks
doesn't make sense at all as we do not have any column named user_id
in table tasks
.
What I did to solve the issue in my case is:
class User < ActiveRecord::Base
has_many :owned_tasks, class_name: "Task", foreign_key: "owner_id"
has_many :assigned_tasks, class_name: "Task", foreign_key: "assignee_id"
end
class Task < ActiveRecord::Base
belongs_to :owner, class_name: "User", foreign_key: "owner_id"
belongs_to :assignee, class_name: "User", foreign_key: "assignee_id"
# Mentioning `foreign_keys` is not necessary in this class, since
# we've already mentioned `belongs_to :owner`, and Rails will anticipate
# foreign_keys automatically. Thanks to @jeffdill2 for mentioning this thing
# in the comment.
end
This way, you can call User.first.assigned_tasks
as well as User.first.owned_tasks
.
Now, you can define a method called tasks
that returns the combination of assigned_tasks
and owned_tasks
.
That could be a good solution as far the readability goes, but from performance point of view, it wouldn't be that much good as now, in order to get the tasks
, two queries will be issued instead of once, and then, the result of those two queries need to be joined as well.
So in order to get the tasks that belong to a user, we would define a custom tasks
method in User
class in the following way:
def tasks
Task.where("owner_id = ? OR assigneed_id = ?", self.id, self.id)
end
This way, it will fetch all the results in one single query, and we wouldn't have to merge or combine any results.