Hello,
Forgot to mention that I am using Postgresql, which gave me an idea to try
using 'DISTINCT ON'
So this is how I've solved it:
class Membership < ActiveRecord::Base
scope :current, -> {at(Date.today)}
def self.at(date)
where("memberships.from <= ?", date).select("DISTINCT ON (user_id) *").
order(:user_id, from: :desc)
end
end
This also gives me an opportunity to get the active membership at any given
date.
I hope this will help for someone.
Cheers,
Tomas
2014 m. lapkritis 26 d., trečiadienis 14:51:31 UTC+2, Mike rašė:
>
> Tomas -
>
> An *option* I've used in the past is to add a datetime field such as
> "dropped_at" that defaults to null to your memberships table.
> From there, you could add a scope to the memberships model like:
>
> class Membership < ActiveRecord::Base
> scope :active, -> { where(dropped_at: nil) }
> end
>
>
> This concept used to be used when you wanted to "soft delete" a record
> from your table,
> but have an option to "undo" the delete. Here, in your instance - you can
> borrow the idea
> to easily find those memberships for a given User that are "active" as
> well as those users
> that are currently a part of a group. The standard created_at field that
> is on the memberships
> table can be used to indicate when a user joined a group.
>
> Hope this helps!
>
> Mike
>
> On Tuesday, November 25, 2014 9:27:27 AM UTC-5, Tomas wrote:
>>
>> Hello,
>>
>> This is a classic User -> Membership -> Group example with some twist:
>> User is a member of a single Group at any given time. But I want to keep
>> the history which Group the User was a member of.
>>
>> I am looking for a proper way of doing it.
>>
>> This is how I think models should look like:
>> #user.rb
>> Class User < ActiveRecord::Base
>> has_many :memberships
>> has_many :groups, through: :memberships
>>
>> #membership.rb
>> Class Membership < ActiveRecord::Base
>> belongs_to :user
>> belongs_to :group
>>
>> #group.rb
>> Class Group < ActiveRecord::Base
>> has_many :memberships
>> has_many :users, through: :memberships
>>
>> Obviously we need date_from attribute in memberships to keep a track on
>> when the user joined the group.
>>
>> Creating/Updating is working out of the box. It's querying data I have
>> trouble with.
>>
>> Now it is easy to get the last group the user is a member of:
>> #user.rb
>> ...
>> def latest_group
>> memberships.order(:date_from).last.group
>> end
>>
>> Similarly you can get latest user for a group.
>>
>> But how to get all users currently belonging to group? Furthermore how to
>> get all the users belonging to group at given date?
>>
>> Looking forward for your input.
>>
>> Cheers
>> Tomas
>>
>>
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