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.
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
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 |
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.
Last modified 2yr ago