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  Issue in display of plot using two level dynamic select options from database tables in Rails
Posted by Raj on Feb-04-2012 07:53
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Hi,

I am facing problem in drawing plots from my database in Rails. Plot is not visible on the browser, even if in the rails log, it says ("sent data"). I am not sure about the problem but it seems related to page replace or data redirection. I am beginner for rails and chart director both.  I have attached the desktop screenshot too.

I will appreciate any help or clue.


-------------------------------------------------------
My Database is as follows:

clusters {id, Name}
nodes {id, cluster_id, name}
node_states{ id, node_id, state_id transition_time}

I want to create a dynamic select option menu to first choose Cluster and then Nodes in that cluster to Plot the state_id Vs transition_time plot for a specific node.

-----------------------------------

I am able to create two level dynamic select option using following code. I am plotting a default figure with node_id = '1' once I open the browser window. However, it is not able to refresh the figure with my final selection of node.
----------------------------------------------------------------------------
----- app/views/node_state_select/index.html.erb

<%= javascript_include_tag :defaults %>
  I want to obtain the State History data for the  Node
  <%= collection_select(:cluster, :cluster_id, Cluster.find(:all), :id, :name,
                      {:prompt => "Select a Cluster"},
                      {:onchange => "#{remote_function(:url  => {:action => "update_nodes"},
                                                       :with => "'cluster_id='+value")}"}) %>
  <div id="nodes"><%= render :partial => 'nodes', :object => @nodes %></div>
</div>


------- app/views/node_states_select/_node.html.erb

<form>
<%= collection_select(:node, :node_id, nodes, :id, :name,
                     {:prompt   => "Select a Node"},
                     {:onchange => "#{remote_function(:url => {:action => "list_node_state"},
                                                       :with => "'node_id='+value")}"}) %>
</form>
<img src="<%= url_for(:action => 'list_node_state', :node_id => (params[:node_id] || '1')) %>">
<br/>

---------------------------------------------------------------------------------

---------------- app/controller/node_states_select_controller.rb
  def update_nodes
       @cluster = Cluster.find(params[:cluster_id])
     nodes = Node.where("cluster_id = ?", @cluster)
       #nodes = @clusters.nodes

       render :update do |page|
         page.replace_html 'nodes', :partial => 'nodes', :object => nodes
       end
  end

  def list_node_state
    c = ChartDirector::XYChart.new(1000, 600, 0xeeeeee, 0x000000, 1)
    c.setPlotArea( 60, 20, 700, 400)
    c.yAxis().setTitle("State Change")
    c.xAxis().setTitle("Time ")
    c.xAxis().setLabelStep(3)

    selectedNode = params[:node_id]
    records = NodeState.where("node_id = ?", selectedNode).order("transition_time")
    time = []
    state = []
    records.each do |r|
      time.push(r.transition_time)
      state.push(r.valid_node_state_id)
    end

    c.addLineLayer(state)
    c.xAxis().setLabels(time)
    c.xAxis().setLabelStep(3)

    # Output the chart
    send_data(c.makeChart2(ChartDirector::PNG), :type => "image/png", :disposition => "inline")
  end

---------------------------------------------------------------------------
dynamicSelect.jpg

  Re: Issue in display of plot using two level dynamic select options from database tables in Rails
Posted by Peter Kwan on Feb-06-2012 23:39
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Hi Raj,

In your browser, you have the following code:

{:onchange => "#{remote_function(:url => {:action => "list_node_state"},
                                                       :with => "'node_id='+value")}"})

The above code executes the list_node_state on the server side, and ignores the returned image. (Your code does not do anything with the returned image.) That is why nothing happens.

As far as I know, even if your code does not ignore the image, standard HTML/Javascript does not allow you to display the image. (There is no HTML/Javascript method to do that.)

For your case, the only method that can update the <IMG> tag is to update the SRC of the <IMG> tag. You can just use plain Javascript to modify the SRC attribute of the <IMG> tag to the URL you want it to use. There is no need to use #remote_function or any AJAX library.

Hope this can help.

Regards
Peter Kwan