Rails - Jul 2007 - Nooby Help with created_at, updated_at, and if/then

Hola. I''m super-new to actually doing things in rails and with ruby, so
pardon me if this is an easy question to everyone else.

I''m making a web app, and at this time am designing the news/blog
portion of it. I have a controller (posts) and a model (post) designed
to coordinate this. I started out with a basic scaffold and went from
there. At this point, I''m trying to get rails to print "Updated by
author on 1/1/07 at 3:45PM" if the updated_at time is different than the
created_at time. Here''s my code:

<% for post in @posts.reverse %>
  <div class="post" id="post<%= post.id %>">
    <h2 id="posttitle<%= post.id %>"
class="posttitleline">
      <%= link_to post.title, {:action => ''show'', :id
=> post}, {:class
=> ''posttitle''} %>
      <%= link_to ''Edit'',{ :action =>
''edit'', :id => post }, { :class =>
''postedit'' } %>
      <%= link_to(image_tag(''destroypost.png''), {:action
=> ''destroy'',
:id => post}, :confirm => ''Are you sure?'', :method =>
:post)%>
    </h2>
    <div id="postbody<%= post.id %>"
class="postbody">
      <%= textilize(post.body) %>
    </div>
    <div id="postfooter<%= post.id %>"
class="postfooter">
      <i>Written by <%= post.author %> on
<%post.created_at.strftime("%B %d, %Y at %I:%M%p") %></i>
    </div>
  </div>
<% end %>

However, that string never shows up, and even weirder is that in the
default scaffold code, the updated_at and created_at values are the same
for every row. For the record, the default scaffold code is this:

<table>
  <tr>
  <% for column in Post.content_columns %>
    <th><%= column.human_name %></th>
  <% end %>
  </tr>

<% for post in @posts %>
  <tr>
  <% for column in Post.content_columns %>
    <td><%=h post.send(column.name) %></td>
  <% end %>
    <td><%= link_to ''Show'', :action =>
''show'', :id => post %></td>
    <td><%= link_to ''Edit'', :action =>
''edit'', :id => post %></td>
    <td><%= link_to ''Destroy'', { :action =>
''destroy'', :id => post },
:confirm => ''Are you sure?'', :method => :post
%></td>
  </tr>
<% end %>
</table>

Any insight? Tips?
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Okay, I''m dumb. I copied that after I deleted the defective code. But 
could anyone show me the best way to do that comparison?

If created_at isn''t equal to updated_at, print "Updated by author
on
1/1/07 at 3:45PM"

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Some might debate this, but I find the best way is to factor the  
whole thing into a helper or a model. E.g.:

# my model.rb

def timestamp_string
   updated_at > created_at ?
     "Updated by #{author} at #{updated_at.to_formatted_s(:short)}" :
     "Created by #{author} at #{created_at.to_formatted_s(:short)}" :
end

# my view.rhtml

<%= post.timestamp_string %>

This should clean up your view. If you feel this couples your model  
too tightly with the display of the data, then create a helper instead.

Does this help?

On Jul 27, 2007, at 12:25 PM, Ben Goering wrote:
>
> Okay, I''m dumb. I copied that after I deleted the defective code.
But
> could anyone show me the best way to do that comparison?
>
> If created_at isn''t equal to updated_at, print "Updated by
author on
> 1/1/07 at 3:45PM"
>
> -- 
> Posted via http://www.ruby-forum.com/.
>
> >

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Steve Ross wrote:
> def timestamp_string
>    updated_at > created_at ?
>      "Updated by #{author} at
#{updated_at.to_formatted_s(:short)}" :
>      "Created by #{author} at
#{created_at.to_formatted_s(:short)}" :
> end
Yes, that should be good for cleaning things up, but I could still use 
some interpretation of this.

How does the:
''updated_at > created_at ?''
line translate?

If updated_at is greater than created_at, then execute this block. Is 
that right?

Does this take into account that I''d rather not have that "Updated
by..." string in there if updated_at and created_at are the same or do I 
need to change this to:

def timestamp_string
    updated_at > created_at ?
      "Updated by #{author} at #{updated_at.to_formatted_s(:short)}"
      "Created by #{author} at #{created_at.to_formatted_s(:short)}"
    else
      "Created by #{author} at #{created_at.to_formatted_s(:short)}"
end

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> def timestamp_string
>    updated_at > created_at ?
>      "Updated by #{author} at
#{updated_at.to_formatted_s(:short)}" :
>      "Created by #{author} at
#{created_at.to_formatted_s(:short)}" :
> end
I''ve not seen the one-line if-then-else statement form like:
   <condition> ? <action_to_do_if_true> :
<action_to_do_if_false>

expanded into MORE than one line. I just tried it in irb. It works --
SORT OF -- but it''s hard to follow. These both work:

true ? 1 : 2

true ?
1 :
2

... generating an output of "1". But you can''t leave anything
out. So
these generate an error:

true ? 1

true ?
1

.. as do:

true ? 1 :

true ?
1 :

Besides, as Ben notes, they''re not clear. So indeed, do it the easy
way:
  def timestamp_string
      if updated_at > created_at
        "Updated by #{author} at
#{updated_at.to_formatted_s(:short)}"
        "Created by #{author} at
#{created_at.to_formatted_s(:short)}"
      else
        "Created by #{author} at
#{created_at.to_formatted_s(:short)}"
      end
  end

But this won''t work either, because methods return only the LAST
assignment statement, unless you include an explicit "return
<expression>". So regardless of the values of updated_at and
created_at, the above would return ONLY the line starting with
"Created by". (Try it in irb.)

Let''s try again, eliminating the duplicate assignment while
we''re at
it. I added an end-of-line character so the strings wouldn''t just run
together. And because you can''t use the "+=" method unless a
variable
has been initialized as a string, number, array, or something similar,
you wind up with something like:

  def timestamp_string
      s = ""
      if updated_at > created_at
        s = "Updated by #{author} at
#{updated_at.to_formatted_s(:short)}\n"
      end
      s += "Created by #{author} at
#{created_at.to_formatted_s(:short)}"
  end

If you REALLY wanted, you could shorten this to:

  def timestamp_string
      updated_at > created_at ? s = "Updated by #{author} at
#{updated_at.to_formatted_s(:short)}\n" : s = ""
      s += "Created by #{author} at
#{created_at.to_formatted_s(:short)}"
  end

---Jim Gagne---


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Did I inadvertently stick a colon at the end of that? Oops. The  
ternary operator, ?, is equivalent to an if/else. So:

updated_at > created_at ? stmt_a : stmt_b

is equivalent to:

if updated_at > created_at
   stmt_a
else
   stmt_b
end

It all depends on what you''re used to.


On Jul 27, 2007, at 1:54 PM, Jim Gagne wrote:
>
>> def timestamp_string
>>    updated_at > created_at ?
>>      "Updated by #{author} at
#{updated_at.to_formatted_s(:short)}" :
>>      "Created by #{author} at
#{created_at.to_formatted_s(:short)}" :
>> end
>
> I''ve not seen the one-line if-then-else statement form like:
>    <condition> ? <action_to_do_if_true> :
<action_to_do_if_false>
>
> expanded into MORE than one line. I just tried it in irb. It works --
> SORT OF -- but it''s hard to follow. These both work:
>
> true ? 1 : 2
>
> true ?
> 1 :
> 2
>
> ... generating an output of "1". But you can''t leave
anything out. So
> these generate an error:
>
> true ? 1
>
> true ?
> 1
>
> .. as do:
>
> true ? 1 :
>
> true ?
> 1 :
>
> Besides, as Ben notes, they''re not clear. So indeed, do it the
easy
> way:
>   def timestamp_string
>       if updated_at > created_at
>         "Updated by #{author} at
> #{updated_at.to_formatted_s(:short)}"
>         "Created by #{author} at
> #{created_at.to_formatted_s(:short)}"
>       else
>         "Created by #{author} at
> #{created_at.to_formatted_s(:short)}"
>       end
>   end
>
> But this won''t work either, because methods return only the LAST
> assignment statement, unless you include an explicit "return
> <expression>". So regardless of the values of updated_at and
> created_at, the above would return ONLY the line starting with
> "Created by". (Try it in irb.)
>
> Let''s try again, eliminating the duplicate assignment while
we''re at
> it. I added an end-of-line character so the strings wouldn''t just
run
> together. And because you can''t use the "+=" method
unless a variable
> has been initialized as a string, number, array, or something similar,
> you wind up with something like:
>
>   def timestamp_string
>       s = ""
>       if updated_at > created_at
>         s = "Updated by #{author} at
> #{updated_at.to_formatted_s(:short)}\n"
>       end
>       s += "Created by #{author} at
> #{created_at.to_formatted_s(:short)}"
>   end
>
> If you REALLY wanted, you could shorten this to:
>
>   def timestamp_string
>       updated_at > created_at ? s = "Updated by #{author} at
> #{updated_at.to_formatted_s(:short)}\n" : s = ""
>       s += "Created by #{author} at
> #{created_at.to_formatted_s(:short)}"
>   end
>
> ---Jim Gagne---
>
>
> >

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That''s why I used the ternary operator. It seems obvious to me that  
the last evaluation will depend on the result of the conditional.

irb(main):001:0> a = 1
=> 1
irb(main):002:0> b = 2
=> 2
irb(main):003:0> a > b ? ''a is greater than b'' :
''a is not greater
than b''
=> "a is not greater than b"
irb(main):004:0> a = 2
=> 2
irb(main):005:0> b = 1
=> 1
irb(main):006:0> a > b ? ''a is greater than b'' :
''a is not greater
than b''
=> "a is greater than b"
irb(main):007:0>


On Jul 27, 2007, at 1:54 PM, Jim Gagne wrote:
> But this won''t work either, because methods return only the LAST
> assignment statement, unless you include an explicit "return
> <expression>".

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Thanks Everyone. Very Helpful :)

On Jul 27, 4:06 pm, "s.ross"
<cwdi...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> That''s why I used the ternary operator. It seems obvious to me
that
> the last evaluation will depend on the result of the conditional.
>
> irb(main):001:0> a = 1
> => 1
> irb(main):002:0> b = 2
> => 2
> irb(main):003:0> a > b ? ''a is greater than b'' :
''a is not greater
> than b''
> => "a is not greater than b"
> irb(main):004:0> a = 2
> => 2
> irb(main):005:0> b = 1
> => 1
> irb(main):006:0> a > b ? ''a is greater than b'' :
''a is not greater
> than b''
> => "a is greater than b"
> irb(main):007:0>
>
> On Jul 27, 2007, at 1:54 PM, Jim Gagne wrote:
>
> > But this won''t work either, because methods return only the
LAST
> > assignment statement, unless you include an explicit "return
> > <expression>".

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