Rails where condition with nil value

Question

I found out that using where with symbol :my_id => nil and using old school one with ? is different. Could anyone explain me why?

MyTable.where(\"my_id = ? \", n         


        

Answer 1

For DB for NULL the syntax should be

my_id IS NULL

So you can give it as:

MyTable.where("my_id is NULL ").first

Answer 2

I suppose it's so called "rails magic" you can pass ranges

Client.where(:created_at => (Time.now.midnight - 1.day)..Time.now.midnight)

becomes

SELECT * FROM clients WHERE (clients.created_at BETWEEN '2008-12-21 00:00:00' 
                                                    AND '2008-12-22 00:00:00')

or if you pass a subset

Client.where(:orders_count => [1,3,5])

rails will do

SELECT * FROM clients WHERE (clients.orders_count IN (1,3,5))

more

Answer 3

In rails 4 you can specify the value as null using the new hash syntax.

MyTable.where(my_id: nil).first

Answer 4

The correct SQL syntax is my_id IS NULL, so if you change your first snippet to the following it will work:

MyTable.where("my_id IS ?", nil).first

Both syntaxes are perfectly fine. It's up to your own preference. However, if it's a parameter and you don't know whether it will be nil or not, you'd better use:

MyTable.where(:my_id => parameter).first

Answer 5

For any relational database the predicate (my_id = NULL ) is always false, because NULL never equals anything - not even NULL.

A more complete explanation is here https://dba.stackexchange.com/questions/166579/why-is-null-ignored-in-query-results/166586#166586.

ActiveRecord will cope with this very well, even when null is included in an array.

irb(main):029:0> Book.where(id: 1).to_sql
=> "SELECT ... WHERE \"books\".\"id\" = 1"
irb(main):030:0> Book.where(id: nil).to_sql
=> "SELECT ... WHERE \"books\".\"id\" IS NULL"
irb(main):031:0> Book.where(id: [1, nil]).to_sql
=> "SELECT ... WHERE (\"books\".\"id\" = 1 OR \"books\".\"id\" IS NULL)"