Return "title" column if "caption" column is empty?

Rails
1

Hi all

Oh my god, this really shouldn’t be a tough one, but I just don’t get
it. :wink:

class Page < ActiveRecord::Base
def caption
caption ? caption : title
end
end

I want to return the content of the title column when the caption column
is empty:

p.caption # Caption is not empty

=> “caption”

p.caption # Caption is empty

=> “title”

Not astonishing, I get a StackLevelTooDeep Exception with my “solution”
above… But how can I do it right?

Thanks a lot… My brain is just a bit wrecked today…
Josh

2

On Wed, Oct 7, 2009 at 11:11 AM, Joshua M.
[email protected] wrote:

class Page < ActiveRecord::Base
def caption
caption ? caption : title
end
end

This will produce an infinite loop. I think you want something more
like

self.caption ? self.caption : self.title

But honestly I’d rename the method to something else for clarity.

–
Greg D.
http://destiney.com/

3

self.caption ? self.caption : self.title

But honestly I’d rename the method to something else for clarity.

Agreed. At some point you’re going to want to access ‘caption’
directly and the above won’t let you do that.

Plus your team might not realize you’re adding magic.

I’ve always gone with “preferred”… that is…

def preferred_caption

code to get me the ideal caption for the fields available

end

That helps remind me that I’m not necessarily getting back the caption
itself, but the ideal caption for the given situation.

It’s worked well for me so far.

-philip

4

Thanks for your useful hints, guys. :slight_smile:

5

Use read_attribute(:caption).

2009/10/7, Joshua M. [email protected]:

end
Not astonishing, I get a StackLevelTooDeep Exception with my “solution”
above… But how can I do it right?

Thanks a lot… My brain is just a bit wrecked today…
Josh

Posted via http://www.ruby-forum.com/.

–
Von meinen Mobilgerät aus gesendet

6

super might work too

def caption
super ? super : title
end

On Oct 7, 5:26 pm, Joshua M. [email protected]

7

Mauricio Szabo wrote:

super might work too

def caption
super ? super : title
end

But it won’t, because caption is not defined on the superclass.

On Oct 7, 5:26�pm, Joshua M. [email protected]

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

8

Mauricio Szabo wrote:

Have you tested it? I tried on a test application, and it works…

Hmm. Maybe ActiveRecord’s method_missing trickery strikes again…

On Oct 8, 9:06�am, Marnen Laibow-Koser <rails-mailing-l…@andreas-

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

9

Have you tested it? I tried on a test application, and it works…

On Oct 8, 9:06 am, Marnen Laibow-Koser <rails-mailing-l…@andreas-

10

def caption
self[:caption] || title
end

On Oct 8, 5:11 am, Joshua M. [email protected]

11

Also I am not sure what rails default is when you just add a
“?”…does it only fail if caption is nil?

I like to do something like this in these scenarios:

def the_caption
self.caption.blank? title : caption
end

I haven’t used read_attribute yet but from the docs it might look
something like this

def caption
caption = read_attribute(:caption)
caption.blank? self.title : caption
end

You get the idea though…just wanted to mention the “blank” part
because if your caption is somehow set to " " I am guessing you want
the title returned.

On Oct 8, 9:43 am, Marnen Laibow-Koser <rails-mailing-l…@andreas-

12

Afaik it has nothing to do with method missing magic. Its just that if
you overwrite a method, a call to super invokes the original method.
AR injects accessor methods for every table column into the class.

2009/10/8, Marnen Laibow-Koser [email protected]:

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

Posted via http://www.ruby-forum.com/.

–
Von meinen Mobilgerät aus gesendet

13

@Joshua - FYI self[:caption] <=> read_attribute(:caption)

@Chris - …and I am guessing interchangeable with self.caption

14

mike wrote:

Afaik it has nothing to do with method missing magic. Its just that if
you overwrite a method, a call to super invokes the original method.

Not really. As far as I know, super calls the method of the same name
in the parent class, which isn’t always the same thing. That’s why we
have alias_method_chain – it wouldn’t be necessary if super worked the
way you claim.

AR injects accessor methods for every table column into the class.

But into the model class itself, not AR::Base. There is no
AR::Base#caption method for super to call. I suspect that super simply
triggers AR’s method_missing, which happens to do the right thing in
this case. But that shouldn’t be relied on as a general rule c

2009/10/8, Marnen Laibow-Koser [email protected]:

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

Posted via http://www.ruby-forum.com/.

–
Von meinen Mobilgerät aus gesendet