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.

belongs_to

has_many through

Last updated 3 months ago

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`