Return filtered records from a returned set of data from two tables - ruby

Question

I have three tables:
- Venue
- Space (belongs to Venue)
- Included Space (belongs to Space)
I receive the id of a Venue in the route and return all the related spaces that I know have Included Spaces(a field called num_included_spaces__c on the Space record that maintains a count of its children). Now that I have all the related parent Spaces for that Venue, I need to find all of the Included Spaces for them.
An Included Space is still a Space, it just happens to have a parent that resides in the same table. I'm trying to turn this:
Venue = Rockdog
- Space = Upstairs
- Space = Media Room
- Space = Courtyard
- Space = Downstairs
- Space = Front Patio
- Space = Indoor Bar
Into this:
Venue = Rockdog
- Space = Upstairs
-- Included Space = Media Room
-- Included Space = Courtyard
- Space = Downstairs
-- Included Space = Front Patio
-- Included Space = Indoor Bar
The Included Spaces table has belongs_to__c and space__c as fields, where belongs_to__c is the id of the parent space and space__c is the id of the child. So i'm looking to find all the Included Spaces where belongs_to_c matches the id of any #spaces returned below
#sub_spaces = Space.where("venue__c = ? AND num_included_spaces__c = ?", params[:venue],0)
#spaces = Space.where("venue__c = ? AND num_included_spaces__c > ?", params[:venue],0)
How would I write this Active Record Query for #included_spaces?

Answer 1

my database schema.
mysql> describe venues;
+------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(255) | YES | | NULL | |
| created_at | datetime | NO | | NULL | |
| updated_at | datetime | NO | | NULL | |
+------------+--------------+------+-----+---------+----------------+
4 rows in set (0,00 sec)
mysql> describe spaces;;
+------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(255) | YES | | NULL | |
| venue_id | int(11) | YES | | NULL | |
| created_at | datetime | NO | | NULL | |
| updated_at | datetime | NO | | NULL | |
+------------+--------------+------+-----+---------+----------------+
5 rows in set (0,00 sec)
ERROR:
No query specified
mysql> describe included_spaces;;
+------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(255) | YES | | NULL | |
| space_id | int(11) | YES | | NULL | |
| created_at | datetime | NO | | NULL | |
| updated_at | datetime | NO | | NULL | |
+------------+--------------+------+-----+---------+----------------+
5 rows in set (0,00 sec)
ERROR:
No query specified
Below function will somehow give you the result you need (in console ofcourse ) however it's not a good solution - it queries database more than needed. However it is the easy -))
def foo id
v = Venue.find(id)
puts v.name
v.spaces.each do |space|
puts space.name
space.included_spaces.each do |spis|
puts spis.name
end
end
end
You can also try a more complex query sth like,
mysql> SELECT spaces.name, included_spaces.name FROM `spaces` INNER JOIN `venues` ON `venues`.`id` = `spaces`.`venue_id` INNER JOIN `included_spaces` ON `included_spaces`.`space_id` = `spaces`.`id` WHERE `spaces`.`venue_id` = 1
-> ;
+------------+-----------+
| name | name |
+------------+-----------+
| Upstairs, | Front |
| Upstairs, | Patio, |
| Upstairs, | Indoor |
| Upstairs, | Bar |
| Downstairs | Media |
| Downstairs | Room, |
| Downstairs | Courtyard |
+------------+-----------+
7 rows in set (0,00 sec)
which should be translated to active record as
Space.joins(:venue)
.joins(:included_spaces)
.where(venue_id: 1)
.select('spaces.name, included_spaces.name')