STI, Single Table Inheritance, supported by ActiveRecord in rails to let us build the models’ hierarchy on a single data table.
Model description
For example, we have a User model, and have an Administrator model, which inherit from User. we can build just one table named ‘user’, and make sure there is a column named ‘type’ and of string type in the User table. like below:
mysql>describe 'user'; +--------------------------+--------------+------+-----+----------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------------------------+--------------+------+-----+----------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | type | varchar(255) | YES | | NULL | | | name | varchar(255) | YES | | NULL | | +--------------------------+--------------+------+-----+----------+----------------+
Code
then, we can writing following code to have a look of STI:
class User < ActiveRecord::Base
validates_presence_of :name
end
class Administrator < User
end
just this, and we can verify it in console:
admin = Administrator.create( :name => "admin") admin.type # "Administrator" admin.id # 1
Concerns
the STI is enabled by default, and so the 'type' in table is likely reserved for STI and we can not using it for other purpose;
and another problem is that if the shared columns are not so much in the model hierarchy, it's a waste using STI, we prefer to setup another table for the child model.
Luckily, we can disable this feature in a table that not using this feature. by doing this:
class User < ActiveRecord::Base
self.abstract_class = true
validates_presence_of :name
end
class Administrator < ActiveRecord::Base
end
Then the 'type' columns in User can be used at our will and there must another table for Administrator alone.