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POHow to (massively) reduce the number of SQL queries in Rails app?
 

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  1. POHow to (massively) reduce the number of SQL queries in Rails app?
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    <p>In my Rails app I have <code>users</code> which can have many <code>invoices</code> which in turn can have many <code>payments</code>.</p> <p>Now in the <code>dashboard</code> view I want to summarize all the <code>payments</code> a <code>user</code> has ever received, ordered either by year, quarter, or month. The <code>payments</code> are also subdivided into <em>gross</em>, <em>net</em>, and <em>tax</em>.</p> <p><strong>user.rb</strong>:</p> <pre><code>class User &lt; ActiveRecord::Base has_many :invoices has_many :payments def years (first_year..current_year).to_a.reverse end def year_ranges years.map { |y| Date.new(y,1,1)..Date.new(y,-1,-1) } end def quarter_ranges ... end def month_ranges ... end def revenue_between(range, kind) payments_with_invoice ||= payments.includes(:invoice =&gt; :items).all payments_with_invoice.select { |x| range.cover? x.date }.sum(&amp;:"#{kind}_amount") end end </code></pre> <p><strong>invoice.rb</strong>:</p> <pre><code>class Invoice &lt; ActiveRecord::Base belongs_to :user has_many :items has_many :payments def total items.sum(&amp;:total) end def subtotal items.sum(&amp;:subtotal) end def total_tax items.sum(&amp;:total_tax) end end </code></pre> <p><strong>payment.rb</strong>:</p> <pre><code>class Payment &lt; ActiveRecord::Base belongs_to :user belongs_to :invoice def percent_of_invoice_total (100 / (invoice.total / amount.to_d)).abs.round(2) end def net_amount invoice.subtotal * percent_of_invoice_total / 100 end def taxable_amount invoice.total_tax * percent_of_invoice_total / 100 end def gross_amount invoice.total * percent_of_invoice_total / 100 end end </code></pre> <p><strong>dashboards_controller</strong>:</p> <pre><code>class DashboardsController &lt; ApplicationController def index if %w[year quarter month].include?(params[:by]) range = params[:by] else range = "year" end @ranges = @user.send("#{range}_ranges") end end </code></pre> <p><strong>index.html.erb</strong>:</p> <pre><code>&lt;% @ranges.each do |range| %&gt; &lt;%= render :partial =&gt; 'range', :object =&gt; range %&gt; &lt;% end %&gt; </code></pre> <p><strong>_range.html.erb</strong>:</p> <pre><code>&lt;%= @user.revenue_between(range, :gross) %&gt; &lt;%= @user.revenue_between(range, :taxable) %&gt; &lt;%= @user.revenue_between(range, :net) %&gt; </code></pre> <p>Now the problem is that this approach works but produces an awful lot of SQL queries as well. In a typical <code>dashboard</code> view I get <strong>100+</strong> SQL queries. Before adding <code>.includes(:invoice)</code> there were even more queries.</p> <p>I assume one of the major problems is that each invoice's <code>subtotal</code>, <code>total_tax</code> and <code>total</code> aren't stored anywhere in the database but instead calculated with every request.</p> <p>Can anybody tell me how to speed up things here? I am not too familiar with SQL and the inner workings of ActiveRecord, so that's probably the problem here.</p> <p>Thanks for any help.</p>
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      1. POHow to (massively) reduce the number of SQL queries in Rails app?
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    1. COYou should look at the SQL requests to find which pieces of information are needed, and use `includes` (as you done for invoice) to include them in the first request. If you can't find it, please add the SQL requests to your question.
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    2. COHave a look at the [bullet gem](https://github.com/flyerhzm/bullet), which detects where you can reduce queries by using eager loading.
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