has_many

Has many represents one of the counter part of belongs to relation. It assumes the current model is referenced by a collection of another model.

Let's see the example used in the chapter belongs_to:

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
)
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

Here, we said a category has many posts. The posts can be accessed through the method posts which return a Collection:

c = Category.query.find!{name == "Technology"} # Retrieve the category named Technology
c.posts.each do |post|
puts "Post name: #{post.name}"
end

Note: The relation can be refined after fetching:

# Fetch only the posts which starts by a digit:
c.posts.where{name =~ /^[0-9]/i}.each do |post|
puts "Post name: #{post.name}"
end

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:

has_many relation_name : RelationType,
foreign_key: "column_name", own_key: "column_name", no_cache: true|false

Argument

Description

Default value

foreign_key

The foreign key which is inside the relative model

[underscore_model_name]_id

own_key

The key against what the relation is tested, primary key by default

self.class.__pkey__

no_cache

Never cache the relation (note: planned feature)

false

Adding to relation

An object can be added into the relation collection using << operator:

c.posts << Post.new({name: "A good post"})

In this case, the post is saved during the add operation.