Questions on scopes

Rails
1

Hey Group,

I am trying to use [what I thought should be] a simple scope for a
message object

scope :unread, where(:read_at => nil)

where the read_at attribute is of type datetime

This is causing the scope to trip a no method error when called upon.

I have a helper method which contains :

if message.read_at == nil
“NEW”
end

and that works fine. however even

scope :unread, where(“read_at == ?”, nil )

does not seem to want to work.

I know I must be missing something terribly obvious about this. Any kick
in the right direction is appreciated.

Thanks

Jesse

2

On Sep 13, 4:16pm, Jesse [email protected] wrote:

I have a helper method which contains :

if message.read_at == nil
“NEW”
end

and that works fine. however even

scope :unread, where(“read_at == ?”, nil )

When comparing with nil you have to use IS NULL rather than the usual
comparison operator. where(:read_at => nil) should work though. How
are you using the scope?

Fred

3

On 9/13/11 12:39 PM, Frederick C. wrote:

scope :unread, where(“read_at == ?”, nil )

When comparing with nil you have to use IS NULL rather than the usual
comparison operator. where(:read_at => nil) should work though. How
are you using the scope?
I am making a call to it through
current_user.received_messages.unread.length which trips a MYSQL Error

|Mysql2::Error: You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near ‘==
NULL)’ at line 1: SELECT message_copies.* FROM message_copies WHERE
(message_copies.recipient_id = 1) AND (read_at == NULL)|

Sorry I figured out the other issue.

4

On Sep 13, 5:51pm, Jesse [email protected] wrote:

On 9/13/11 12:39 PM, Frederick C. wrote:

When comparing with nil you have to use IS NULL rather than the usual
comparison operator. where(:read_at => nil) should work though. How
are you using the scope?

I am making a call to it through
current_user.received_messages.unread.length which trips a MYSQL Error

|Mysql2::Error: You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use near ‘==
NULL)’ at line 1: SELECT message_copies.* FROM message_copies WHERE
(message_copies.recipient_id = 1) AND (read_at == NULL)|

is that using where(“read_at == ?”, nil ) ? That’s just invalid
syntax, since the comparison operator operator is = in SQL. NULL is a
special case though - use IS NULL/IS NOT NULL to test for null values.

Fred

5

On 9/13/11 1:04 PM, Frederick C. wrote:

is that using where(“read_at == ?”, nil ) ? That’s just invalid
syntax, since the comparison operator operator is = in SQL. NULL is a
special case though - use IS NULL/IS NOT NULL to test for null values.
Thanks, that did the trick.