Rails - Feb 2011 - accessing the field of a model that belongs to another model using dot notation

Hey all,

with this below (a post has many blog_images and blog_image belongs to
post):

<% @posts.each do |post| %>

    <div class="FeatureItem">
        <a href=""><img
src="/images/<%post.blog_images.image_file_name %>"
width="220" height="174" alt=""
style="top: 27px; left: 13px;" />Click Here</a>

        <div class="FeatureContent">
          <h2><a href=""><%= post.title
%></a></h2>
          <p><%= post.body %></p>
          <p class="posted"><%= post.user_id %></p>

        </div>
    </div>
<% end %>

I get undefined method image_file_name because image_file_name is a
field in blog_images table. So activerecord generates field names as
instance methods but above I''m trying to use it as a class method, so
since there is no class method image_file_name in BlogImage class, it
throws error. Is there  a way that I can get image_file_name without
creating a class mehtod because I want to pull the data dynamically from
the table, where  the image file belongs to blog post.

Thanks for response.

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

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

On Thu, Feb 24, 2011 at 11:47 AM, John Merlino
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> Hey all,
>
> with this below (a post has many blog_images and blog_image belongs to
> post):
>
> <% @posts.each do |post| %>
>
>    <div class="FeatureItem">
>        <a href=""><img src="/images/<%>
post.blog_images.image_file_name %>" width="220"
height="174" alt=""
> style="top: 27px; left: 13px;" />Click Here</a>
>
>        <div class="FeatureContent">
>          <h2><a href=""><%= post.title
%></a></h2>
>          <p><%= post.body %></p>
>          <p class="posted"><%= post.user_id
%></p>
>
>        </div>
>    </div>
> <% end %>
>
>
you problem here is that post.blog_images returns an array of blog_images.
so the
error is thrown since you''re calling image_file_name on an array
object.
 try

post.blog_images.first.image_file_name

> I get undefined method image_file_name because image_file_name is a
> field in blog_images table. So activerecord generates field names as
> instance methods but above I''m trying to use it as a class method,
so
> since there is no class method image_file_name in BlogImage class, it
> throws error. Is there  a way that I can get image_file_name without
> creating a class mehtod because I want to pull the data dynamically from
> the table, where  the image file belongs to blog post.
>
> Thanks for response.
>
> --
> Posted via http://www.ruby-forum.com/.
>
> --
> You received this message because you are subscribed to the Google Groups
> "Ruby on Rails: Talk" group.
> To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To unsubscribe from this group, send email to
>
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> For more options, visit this group at
> http://groups.google.com/group/rubyonrails-talk?hl=en.
>
>

-- 
-------------------------------------------------------------
visit my blog at http://jimlabs.heroku.com

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Phil


On Wed, Feb 23, 2011 at 9:47 PM, John Merlino
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> Hey all,
>
> with this below (a post has many blog_images and blog_image belongs to
> post):
>
> <% @posts.each do |post| %>
>
>    <div class="FeatureItem">
>        <a href=""><img src="/images/<%>
post.blog_images.image_file_name %>" width="220"
height="174" alt=""
> style="top: 27px; left: 13px;" />Click Here</a>
>
>        <div class="FeatureContent">
>          <h2><a href=""><%= post.title
%></a></h2>
>          <p><%= post.body %></p>
>          <p class="posted"><%= post.user_id
%></p>
>
>        </div>
>    </div>
> <% end %>
>
> I get undefined method image_file_name because image_file_name is a
> field in blog_images table. So activerecord generates field names as
> instance methods but above I''m trying to use it as a class method,
so
> since there is no class method image_file_name in BlogImage class, it
> throws error. Is there  a way that I can get image_file_name without
> creating a class mehtod because I want to pull the data dynamically from
> the table, where  the image file belongs to blog post.
>
> Thanks for response.
>
>
You can''t call image_file_name on post.blog_images, because
post.blog_images
returns an array, and the array doesn''t have a method called
image_file_name. Check something like map; eg:
post.blog_images.map(&:image_file_name).


> --
> Posted via http://www.ruby-forum.com/.
>
> --
> You received this message because you are subscribed to the Google Groups
> "Ruby on Rails: Talk" group.
> To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To unsubscribe from this group, send email to
>
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> For more options, visit this group at
> http://groups.google.com/group/rubyonrails-talk?hl=en.
>
>
-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

Thanks for replies.

This:

post.blog_images.first.image_file_name

outputs

undefined method `image_file_name'' for nil:NilClass

I think that means I called a method on a class that it cannot find? I 
have already established has_many belongs_to between blog_images and 
posts table.

This doesn''t return error but doesn''t output anything:

post.blog_images.map(&:image_file_name)

Although there are values in the image_file_name field of blog_images 
table. And if I was to hard code that value in url, it would work, so 
that map isn''t doing what''s expected of it.

ANy suggestions?

thanks for response.

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

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

On Fri, Feb 25, 2011 at 11:28 AM, John Merlino
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> post.blog_images.first.image_file_name
>
> outputs
>
> undefined method `image_file_name'' for nil:NilClass
>
> I think that means I called a method on a class that it cannot find?
It means that this particular ''post'' has no
''blog_images'' associated
with it; the array is empty so of course ''first'' is nil ...

-- 
Hassan Schroeder ------------------------
hassan.schroeder-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
twitter: @hassan

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

On 25 February 2011 19:28, John Merlino
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> post.blog_images.first.image_file_name
>
> outputs
>
> undefined method `image_file_name'' for nil:NilClass
That means that in your chain of method calls, the thing before
"image_file_name" is nil. So there is no "first" record in
the
blog_images collection... are you sure you have some associated
images?

I tend to find using a "guard" helps in chained calls like this:
  post.blog_images.first.image_file_name if post.blog_images.first

or even (when necessary)
  foo.bar.baz.method_name if foo.bar && foo.bar.baz

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

> That means that in your chain of method calls, the thing before
> "image_file_name" is nil. So there is no "first" record
in the
> blog_images collection... are you sure you have some associated
> images?
Yes, in my database I have blog_images table with a foreign key of 
blog_post_id of 1. In my blog_posts table, I have a record with a 
primary key of 1. So there should be at least one association.

Thanks for response

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

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

On 25 February 2011 21:02, John Merlino
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
>> That means that in your chain of method calls, the thing before
>> "image_file_name" is nil. So there is no "first"
record in the
>> blog_images collection... are you sure you have some associated
>> images?
>
> Yes, in my database I have blog_images table with a foreign key of
> blog_post_id of 1. In my blog_posts table, I have a record with a
> primary key of 1. So there should be at least one association.
Do you know how to use ruby-debug to break into your code and inspect
data.  If not have a look at the Rails Guide on debugging.  Then you
can break in before the problem line and inspect things to see what is
the problem.

Also you have not said what happens if you include the test checking
for no blog_images.

Colin

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

> Also you have not said what happens if you include the test checking
> for no blog_images.
>
> Colin
I think I realized what the problem was. There were four records in the 
blog_posts table. At the time of the post, I only had one record in 
blog_images table that linked to first record of blog_posts. What this 
is doing:

post.blog_images.first.image_file_name

it is iterating for each post the first image_file_name linked to it. So 
the time it iterates through the second post, since there is not  an 
image_file_name associated with it, it throws the exception since the 
array object has no image_file_name method!

This was data error on my part. But adding that if is what made me 
realize it:

<img src="/images/<%= post.blog_images.first.image_file_name if 
post.blog_images.first %>" width="220" height="174"
alt="" style="top:
27px; left: 13px;" />

Thanks for all responses.

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

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.