Why is Rails is adding `OR 1=0` to queries using the where clause hash syntax with a range?

Question

The project that I'm working on is using MySQL on RDS (mysql2 gem specifically).

When I use a hash of conditions including a range in a where statement I'm getting a bit of an odd addition to my query.

User.where(id: [1..5])

and

User.where(id: [1...5])

Result in the following queries respectively:

SELECT `users`.* FROM `users` WHERE ((`users`.`id` BETWEEN 1 AND 5 OR 1=0))
SELECT `users`.* FROM `users` WHERE ((`users`.`id` >= 1 AND `users`.`id` < 5 OR 1=0))

The queries work perfectly fine since OR FALSE is effectively a no-op. I'm just wondering why Rails or ARel is adding this snippet into the query.

EDIT

It looks like the line that could explain this is line 26 in ActiveRecord::PredicateBuilder. Still no idea how the hash could be empty? at that point but maybe someone else does.

EDIT 2

This is intersting. I was looking into Filip's comment to see why he made it since it seems just like a clarification but he is correct that 1..5 != [1..5]. The former is an inclusive range from 1 to 5 where as the latter is an array whose first element is the former. I tried putting these into an ARel where call to see the SQL produced and the OR 1=0 is not there!

User.where(id: 1..5) #=> SELECT "users".* FROM "users"  WHERE ("users"."id" BETWEEN 1 AND 5)
User.where(id: 1...5) #=> SELECT "users".* FROM "users"  WHERE ("users"."id" >= 1 AND "users"."id" < 5)

While I still do not know why ARel is adding the OR 1=0 which will always be false and seemingly unnecessary. It may be due to how Arrays and Ranges are handled differently.

Answer 1

Building on the fact, which you've discovered, that [1..5] is not the correct way to specify the range... I have discovered why [1..5] behaves as it does. To get there, I first found that an empty array in a hash condition produces the 1=0 SQL condition:

User.where(id: []).to_sql
# => "SELECT \"users\".* FROM \"users\"  WHERE 1=0"

And, if you check the ActiveRecord::PredicateBuilder::ArrayHandler code, you'll see that array values are always partitioned into ranges and other values.

ranges, values = values.partition { |v| v.is_a?(Range) }

This explains why you don't see the 1=0 when using non-range values. That is, the only way to get 1=0 from an array without including a range is to supply an empty array, which yields the 1=0 condition, as shown above. And when all the array has in it is a range you're going to get the range conditions (ranges) and, separately, an empty array condition (values) executed. My guess is that there isn't a good reason for this... it just simply is easier to let this be than to avoid it (since the result set is equivalent either way). If the partition code was a bit smarter then it wouldn't have to tack on the additional, empty values array and could skip the 1=0 condition.

As for where the 1=0 comes from in the first place... I think that comes from the database adapter, but I couldn't find exactly where. However, I would call it an attempt to fail to find a record. In other words, WHERE 1=0 isn't ever going to return any users, which makes sense over alternative SQL like WHERE id=null which will find any users whose id is null (realizing that this isn't really correct SQL syntax). And this is what I'd expect when attempting to find all Users whose id is in the empty set (i.e. we're not asking for nil ids or null ids or whatever). So, in my mind, leaving the bit about exactly where 1=0 comes from as a black box is OK. At least we now can reason about why the range inside of the array is causing it to show up!

UPDATE

I've also found that, even when using ARel directly, you can still get 1=0:

User.arel_table[:id].in([]).to_sql
# => "1=0"

Answer 2

This is strictly speaking a guess, since I did something similar in a project of my own (although I used AND 1).

For whatever reason, when generating a query, it is easier to always have a WHERE clause containing a no-op than it is to conditionally generate the WHERE clause at all. That is, if you don't include any where sections it will end up generating something still valid.

On the other hand, I'm not sure why it's taking this form: when I did it I use 1 [<AND (generated code)>...] it allowed arbitrary chaining, but I don't see how what you're seeing would allow it. None the less, I still think it likely to be a result of an algorithmic code generation scheme.

Answer 3

Check to see if you are using active_record-acts_as. That was the problem with me.

Add the line below to your Gemfile:

gem 'active_record-acts_as', :git => 'https://github.com/hzamani/active_record-acts_as.git'

This will just pull the latest version of the Gem that will hopefully be fixed. Worked for me.

Answer 4

I think you're seeing side effects of ruby personally.

I think the better way to do what you're doing would be with

2.0.0-p481@meri :008 > [*1..5]
 => [1, 2, 3, 4, 5]

User.where(id: [*1..5]).to_sql
"SELECT `users`.* FROM `users`  WHERE `users`.`id` IN (1, 2, 3, 4, 5)"

As this creates an Array vs an Array with element 1 of class Range.

OR

use an explicit Range to trigger the BETWEEN in AREL.

# with end element, i.e. exclude_end=false
2.0.0-p481@meri :013 > User.where(id: Range.new(1,5)).to_sql
=> "SELECT `users`.* FROM `users`  WHERE (`users`.`id` BETWEEN 1 AND 5)"

# without end element, i.e. exclude_end=true
2.0.0-p481@meri :022 > User.where(id: Range.new(1, 5, true)).to_sql
 => "SELECT `users`.* FROM `users`  WHERE (`users`.`id` >= 1 AND `users`.`id` < 5)"

Answer 5

If you care about having control of the queries you generate and the full power of the SQL language and database features then I would suggest moving from ActiveRecord/Arel to Sequel.

I can honestly say there are a lot more quirks and infuriating times ahead for you with ActiveRecord, especially when you move beyond simple crud like queries. When you start trying to query your data in anger, perhaps needing to join a few join tables here and there and realize you really do need join conditions or union all type queries.

It is also significantly faster and more reliable in its query generation and result handling and much easier to compose the queries you want. It also has real documentation you can actually read unlike arel.

I just wish I had discovered it much earlier rather than persisting with the rails default data access layer.