On Sunday, December 3, 2017 at 7:51:15 PM UTC-8, tdrive wrote:
>
> I'm trying to rewrite my project from AR to Sequel and I have a problem.
>
> For examle we have tables
> create_table :users do |t|
> t.string :name
> end
>
> create_table :relations do |t|
> t.string :type
> t.integer :user_id
> t.integer :with_user_id
> end
>
> and models
> class Relation::Base < ActiveRecord::Base
> self.table_name = :relations
>
> belongs_to :user
> belongs_to :with_user, class_name: "User"
> end
>
> class Relation::Colleague < Relation::Base
> end
>
> class Relation::Friend < Relation::Base
> end
>
> class User < ActiveRecord::Base
> has_many :friend_relations, class_name: "Relation::Friend"
> has_many :colleague_relations, class_name: "Relation::Colleague"
>
> has_many :friends, through: :friend_relations, source: :with_user,
> class_name: "User"
> has_many :colleagues, through: :colleague_relations, source: :with_user,
> class_name: "User"
> end
>
>
> How should I rewrite the :friends and :colleagues associations without
> hardcoded conditions type='Relation::Colleague' and type='Relation::Friend
> '
>
Sequel doesn't ship with support for polymorphic associations, so if you
want it in Sequel you have to hardcode the conditions, with something like:
class User
many_to_many :friends, join_table: :relations, right_key: :with_user_id,
class: self do |ds|
ds.where{relations[:type] =~ 'Relation::Friend'}
end
end
These types of associations are fairly easy to metaprogram by using a loop
to handle all your polymorphic types.
There is the sequel_polymorphic external plugin that you could try,
especially if you want easier access to modify such polymorphic
associations. Alternatively, split your polymorphic join table into
separate tables for friends and colleagues and then you don't need any
polymorphism and can benefit from the increased simplicity and the ability
to enforce referential integrity in the database.
Thanks,
Jeremy
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