Question

I am having trouble accessing the correct information in my rails model (which I believe to be correct) The schema for my tables are

create_table :schools do |t|
    t.string :name
    t.timestamps
end  

create_table :variables do |t|
    t.string :name
    t.string :category
    t.timestamps
end

create_table :data do |t|
    t.string :entry
    t.decimal :rank, :scale => 3
    t.integer :school_id, :null => false
    t.integer :variable_id, :null => false
    t.timestamps
end

Model classes:

class Datum < ActiveRecord::Base
    belongs_to :school
    belongs_to :variable
end

class School < ActiveRecord::Base
    has_many :data
    has_many :variables, :through => :data
end

class Variable < ActiveRecord::Base
    has_many :data
    has_many :schools, :through => :data
end

here is my school show.html.erb page currently:

<h2> <%= @school.name %> </h2>

<table>
<% @school.variables.each  do |variable| %>
<tr><tr/>
<td><%= variable.name %></td>
<td><%= Datum.find(:first, :conditions => {:school_id => @school.id, :variable_id => variable.id}).entry %></td> 
<td><%= link_to 'Edit', edit_school_path(@school) %></td>
<td><%= link_to 'Back', schools_path %></td>
<% end %>
</table>  

It does what I want it to but it does wayy to many queries. I’m assuming I have to do eager loading but based on examples I found online I couldn’t figure out how to do this (I’m really new to rails). Does anyone have any ideas?

Answer 1

Try this and see if you get the results you expect, as well as a reduced number of queries.

Datum.find(:first, 
           :conditions => {:school_id => @school.id, :variable_id => variable.id}, 
           :include => [:school, :variable])

Also, MVC principles dictate that you shouldn’t do the find in your view; instead, in the controller’s method (app/controllers/school_controller.rb, method show) do

@data = Datum.find(....)

and in the view:

<%= @data.entry %>

That way you don’t pollute your view with DB access concerns.