link_to passing paramater and display problem - tag feature - Ruby on Rails

Question

I have gotten a great deal of help from KandadaBoggu on my last question and very very thankful for that. As we were getting buried in the comments I wanted to break this part out.

I am attempting to create a tag feature on the rails blog I am developing. The relationship is Post has_many :tags and Tag belongs_to :post. Adding and deleting tags to posts are working great.

In my /view/posts/index.html.erb I have a section called tags where I am successfully querying the Tags table, grouping them and displaying the count next to the tag_name (as a side note, I mistakenly called the column containing the tag name, 'tag_name' instead of just 'name' as I should have) . In addition the display of these groups are a link that is referencing the index method in the PostsController. That is where the problem is.

When you navigate to /posts you get an error because there is no parameter being passed (without clicking the tag group link). I have the .empty? in there so not sure what is going wrong here. Here is the error and code:

Error

You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.empty?

/views/posts/index.html.erb

<% @tag_counts.each do |tag_name, tag_count| %> 
            <tr>
                <td><%= link_to(tag_name, posts_path(:tag_name => tag_name)) %></td>
                <td>(<%=tag_count%>)</td>
            </tr>
        <% end %>

PostsController

  def index
    @tag_counts = Tag.count(:group => :tag_name, :order => 'updated_at DESC', :limit => 10)
    @posts=Post.all(:joins => :tags,:conditions=>(params[:tag_name].empty? ? {}: 
                     { :tags => { :tag_name => params[:tag_name] }}
                     )
                  )

    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @posts }
      format.json { render :json => @posts }
      format.atom
    end
  end

Answer 1

Here where you are calling empty?, if params[:tag_name] is nil, it will raise the error you are seeing.

@posts=Post.all(:joins => :tags,:conditions=>(params[:tag_name].empty? ? {}: 
                     { :tags => { :tag_name => params[:tag_name] }}
                     )
                  )

If you just care whether it is nil or not, you can take advantage of the fact that nil is falsey and do this

@posts=Post.all(:joins => :tags,:conditions=>(params[:tag_name] ? 
                     { :tags => { :tag_name => params[:tag_name] }} : {}

                     )
                  )

But that is pretty ugly. It might be better to do something like this to make it clearer what you are doing:

@posts = if params[:tag_name]
           Post.all
         else
           Tag.find_by_name(params[:tag_name], :include => :posts).posts
         end

Answer 2

When I gave you the solution, I had forgotten the fact that I had monkey patched my Nil class with a empty? method. That is the reason why it is not working for you.

Change the code as follows:

conditions, joins = {}, nil
unless(params[:tag_name] || "").empty?
  conditions = ["tags.tag_name = ? ", params[:tag_name]]
  joins = :tags
end
@posts=Post.all(:joins => joins, :conditions=> conditions)

Edit 1

The code above performs empty check instead of nil check. I always make it a practice to perform a empty check for query parameters. This covers the cases where the action is invoked from a search form. In such cases tag_name will not be nil but an empty string.

Edit 2

Fixed the multiple row issue.

Edit 3

I fixed the posts no show issue when tag names are present.

Edit 4

In order to get the count in DESC order remove the the order clause from your count call.

@tag_counts = Tag.count(:group => :tag_name, :limit => 10)

The count method returns a ordered hash sorted by count. You changed the default sort order by adding the order clause.