SQL » Joins
To load associated relations you can simply use join, left_join, or right_join.
Using joins with relations
class Users < ROM::Relation[:sql]
schema(infer: true) do
associations do
has_many :tasks
has_many :posts
end
end
def with_tasks
join(tasks)
end
def with_posts
left_join(posts)
end
end
Auto-qualifying
When you pass a relation as the argument for join methods, the resulting relation will have all attributes qualified automatically for you
Using joins with explicit name and options
If you want to have more control, you can pass table name and additional options yourself:
class Users < ROM::Relation[:sql]
schema(infer: true) do
associations do
has_many :tasks
has_many :posts
end
end
def with_tasks
join(:tasks, user_id: :id, priority: 1)
end
def with_posts
left_join(:posts, user_id: :id)
end
end
Using joins with additional options
The second option hash can be used too, if you want to provide more options:
class Users < ROM::Relation[:sql]
schema(infer: true) do
associations do
has_many :tasks
has_many :posts
end
end
def with_tasks
join(:tasks, { user_id: :id }, table_alias: :user_tasks)
end
def with_posts
left_join(posts, { user_id: :id }, table_alias: :user_posts)
end
end
Learn more
Check out API docs: