ruby on rails - Creating has_one association within the same model -

let consider below model.

user{ id:number(primary_key), column1:string, column2:string) 

now, column1 can string, column2 can either null, or have values column1. column1 , column2 can't same. i.e. column2 foreign key , reference column1.

how create has_one relationship these constraints.

something like,

has_one :master_agreement, :class_name => 'user', :foreign_key => 'column2', :primary_key => 'column1' 

but above mentioned doesn't work me.

to setup self-joining relationship in rails want use belongs_to not has_one key difference belongs_to places foreign key column on model's table - while has_one places on other end.

class user < activerecord::base   belongs_to :company # references users.company_id   has_one :company # references companies.user_id end 

lets consider system have hierarchy of categories:

class category < activerecord::base   belongs_to :parent, class_name: 'category'   has_many :subcategories, class_name: 'category', foreign_key: 'parent_id' end  

this creates self joining relationship categories.parent_id foreign key column references categories.id.

while potentially use different categories.id reference making things harder on id column indexed primary key column.