belongs_to

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?

Argument	Description	Default value
foreign_key	The column used by the relation	[underscore_model_name]_id
primary	Set to true if the foreign_key is also the primary key of this table	false
key_type	The type of the column. Set to the primary key type of the relative table.	Int64?
no_cache	Never cache the relation (note: planned feature)	false