Help Converting from SQL to Rails syntax

Rails
#1

Hi all,

I have a table where I’m deleting sparse records – basically cleaning
up
broken has_many / belongs_to relationships. (How we get into this
situation
is a trade-off. We can have '000’s of records, and deletes generally
happening during peak load, so we just do the clean up later.)

I have ModelA and ModelB. ModelB belongs_to ModelA. ModelA has_many
ModelB

Anyway, I have figured out the SQL I want (MySQL:

DELETE

  model_a_table

FROM

  model_a_table

  left join model_b_table on model_a_table.model_b_id =

model_b_table.id

WHERE

  model_b_table.id is NULL;

I believe I have the equivalent SELECT figured out as:
ModelA.includes(:model_b).where(:model_b => {:id => nil})

However, I can’t seem to get the equivalent delete working. Adding
delete_all to the end of the relationship ‘breaks’ the includes and
causes
the where to fail.

I’m going to try and figure this out with the
old syntax (ModelA.delete(:conditions…)). Thought I’d ask here first
as
it seems like I should be able to pretty easily convert the SELECT I
have
to an equivalent delete operation.

Thanks in advance.

#2

worth noting, since I could have '000’s of records, the point of this is
to
avoid having to load the ids I want to delete into the app and let the
DB
optimize for it.

#3

I am a little confused here. If ModelB belongs to ModelA, I think your
foreign key relationship is backwards. The model_b_table should have a
foreign key to model_a_id, not the other way around.

Regardless, though, you can pass conditions to delete_all which should
help
you accomplish what you want.

ModelA.delete_all(“model_b_id is null”)

#4

Thanks for trying to decipher my problem. I may have made an error in my
description of the problem.

Regardless, after much digging, what I am looking for is not currently
possible.
https://github.com/rails/rails/issues/919