Update of nested join not working with an order - mysql

Question

Long time reader, first time poster. (I did some deep dive searches, and was unable to find anything similar -- Thank you in advance)
I am coding a project using ruby and active record, and I ran into a situation where I'm not able to google search the answer to why two things are happening. From what I can tell, the first thing is happening because of a known bug with rails. The second, I do not know.
Here's the mock code:
class Object1 < ActiveRecord::Base
has_many :object2s, foreign_key: :object1_id, :dependent => :delete_all
end
class Object2 < ActiveRecord::Base
belongs_to :object1, class_name: "Object1"
end
Object2 has a unique index for object1_id and date.
I have an update that is failing due to a index violation:
ActiveRecord::RecordNotUnique in Object1Controller#datechange
Update code:
Object2.joins( :object1 ).where( object1: { :id => id } )**.order( obj2_date: ascdsc )**.update_all(
"obj2_date = " + direction + "(obj2_date, INTERVAL " + difference.to_s + " month)")
The index is being tripped on the update without the order (** added above), the dates are being updated in a way that causes the violation. Elsewhere in the code, I have specified the update order, and it will update them in a way that will not violate the index. With this Object, adding in the join causes the first issue:
Here's the (mock) SQL generated:
UPDATE object2 SET obj2_date = date_sub(obj2_date, INTERVAL 1 month)
WHERE object2.id IN (
SELECT id FROM (
SELECT object2.id FROM object2 INNER JOIN object1 ON object1.id = object2.object1_id WHERE <criteria> **ORDER BY object2.obj2_date ASC**
) __active_record_temp
)
If I modify the SQL, I can run it in an SQL client where it will work as expected. [Note: I moved the location of the order]
UPDATE object2 SET obj2_date = date_sub(obj2_date, INTERVAL 1 month)
WHERE object2.id IN (
SELECT id FROM (
SELECT object2.id FROM object2 INNER JOIN object1 ON object1.id = object2.object1_id WHERE <criteria>
) __active_record_temp
) **ORDER BY object2.obj2_date ASC**
Question 1:
The order is being added to the wrong place. How do I get it right, or work around it?
I believe this to be related to this bug:
https://github.com/rails/rails/issues/6769
Question 2:
Why is this happening? ...select id from (select id from table) __temp_table...
WHERE object2.id IN (
SELECT id FROM (
SELECT object2.id FROM object2 INNER JOIN object1 ON object1.id = object2.object1_id WHERE <criteria> **ORDER BY object2.obj2_date ASC**
) __active_record_temp
)
Wouldn't it be better for it to be this: ...select id from table...
WHERE object2.id IN (
SELECT object2.id FROM object2 INNER JOIN object1 ON object1.id = object2.object1_id WHERE <criteria>
)
Removing the need for a temp table just to get the id when it's already getting just the id?
Thanks.

Answer 1

I really don't get why the Order should matter so much, but simply add
LIMIT 18446744073709551615
behind your ORDER mBY
UPDATE object2 SET obj2_date = date_sub(obj2_date, INTERVAL 1 month)
WHERE object2.id IN (
SELECT DISTINCT id FROM (
SELECT object2.id,object2.obj2_date FROM object2 INNER JOIN object1 ON object1.id = object2.object1_id WHERE <criteria>
) __active_record_temp
ORDER BY obj2_date ASC LIMIT 18446744073709551615
)
The cause, why order by are ignored without a LIMIT is simple, rows are per definition unordered so teh ORDER BY is removed without a Limit,
Mysql lets the ORDER BY untouched under special circumstances
Object2.joins( :object1 ).where( object1: { :id => id } ).order( obj2_date: ascdsc ).limit(18446744073709551615).update_all(
"obj2_date = " + direction + "(obj2_date, INTERVAL " + difference.to_s + " month)")

Answer 2

I didn't know you could have an entire active record code block inside an active record code block.
This addresses both issues. Code:
Object2.where( id: __Object1.select( :id ).where( :parent_id => id )__ ).order( obj2_date: ascdsc ).update_all(
"obj2_date = " + direction + "(obj2_date, INTERVAL " + difference.to_s + " month)")
Auto generates this SQL:
UPDATE object2 SET obj2_date = date_add(obj2_date, INTERVAL 1 month)
WHERE object2.obj1_id IN (
SELECT object1.id FROM object1 WHERE object1.parent_id = 15
) ORDER BY object2.obj2_date ASC