DEV Community

Discussion on: Why is Rails ActiveRelation.update_all updating a different set of records?

View post
Collapse
 
phallstrom profile image
Philip Hallstrom • • Edited

What is the SQL generated by related_comments.count. Count will change the query sometimes if Rails decides it doesn't need the join/includes. I'm guessing it's dropping your union -- or simply not doing it correctly. And that's what is leading to the difference in rows affected.

edit: however your second solution suggests i'm wrong about that. still, would be curious to see the SQL if you just run the query to select them and for the count.

Collapse
 
andy profile image
Andy Zhao (he/him) •

Here's the SQL for related_comments.count:

(22.0ms)  SELECT COUNT(*) FROM ( (SELECT "comments".* FROM "comments"
WHERE (("comments"."ancestry" LIKE '12/%' OR "comments"."ancestry" = '12')
OR "comments"."id" = 12)) UNION (SELECT "comments".* FROM "comments" WHERE
1=0 ORDER BY COALESCE("comments"."ancestry", '') ASC) ) "comments" WHERE
"comments"."user_id" = $1  [["user_id", 11]] [sql_query]

And for the select:

(4.1ms)  SELECT "comments".* FROM ( (SELECT "comments".* FROM "comments"
WHERE (("comments"."ancestry" LIKE '12/%' OR "comments"."ancestry" = '12')
OR "comments"."id" = 12)) UNION (SELECT "comments".* FROM "comments" WHERE
1=0 ORDER BY COALESCE("comments"."ancestry", '') ASC) ) "comments" WHERE
"comments"."user_id" = $1  [["user_id", 11]] [sql_query]

FWIW the code I'm using does not run related_comments.count; that was to demonstrate how many records should be updated.