Belongs to represents an association where the associated object share its primary key in a column of the current object. Let's give an example:

CREATE TABLE categories (
    id bigserial NOT NULL PRIMARY KEY, 
    name text NOT NULL
)
​
CREATE TABLE posts (
    id bigserial NOT NULL PRIMARY KEY,
    name text NOT NULL,
    content text,
    category_id bigint NOT NULL
)

In this case, Post belongs to categories, as it maintain a link to the category through category_id column.

In clear, this relation can be written like this:

class Post
  include Clear::Model
​
  primary_key
​
  column name : String
  column content : String?
​
  belongs_to category : Category
end
​
class Category
  include Clear::Model
  primary_key
​
  column name : String
​
  has_many posts : Post
end

• Clear will take care for you of the declaration of the column category_id

• You may notice has_many in Category model. We will go further onto it in the next chapter.

Customizing the relation

Clear uses naming convention to infer the name of the foreign key. You may want to override this behavior by adding some parameters:

belongs_to relation_name : RelationType, 
    foreign_key: "column_name", primary: true|false, 
    key_type: AnyType?