How to check if a parent has children?

rubyonrails-talk
1

What is the new way to check if a parent has child items? In rails 1.2.6 I did this:

if @client.has_line_items?

Client being the parent and line_items the children.

Now that I have upgraded to rails 2.0.1 (on my way to current :slight_smile: ) I am getting this message:

undefined method `has_line_items?' for #<Client:0x7f3b093b01a0>

How should I format the query now?

Regards,

Paul Thompson

2

Paul,

if @client.line_items.exists?

Anthony Crumley http://commonthread.com

3

Thanks Anthony,

It's better, but I'm not quite there yet. I am now getting:

wrong number of arguments (0 for 1)

Regards,

Paul Thompson

4

Paul,

Sorry, but I gave you the wrong method. It should have been …

unless @client.line_items.empty?

Anthony Crumley http://commonthread.com

5

Thanks Anthony,

Did a little more homework and decided to use:

unless @client.line_items.blank?

as .blank? will not bomb on a nil condition and .empty? will.

But thanks very much for pointing me in the right direction.

Regards,

Paul Thompson

6

Not sure why you'd want to do that - if a has_many is returning nil (rather than an empty array) something has gone terribly, terribly wrong. Also, .blank? isn't proxied like .empty? is - blank? will load the association then call the method; empty? is defined in AssociationCollection to do a direct SQL query if the association isn't loaded, potentially skipping a bunch of unneeded object creation.

Certainly not a big deal, but worth following the standard API for efficiency's sake.

--Matt Jones