Question

I want to sum columns.

In my controller

         def index
          @performance_reports = PerformanceReport.all
         end

My error:

       undefined method `+' for #<PerformanceReport:0x4a55690>
74:         <td><%=  @performance_reports.sum(:clicks)%></td>

What is wrong ?

Answer 1

try

 @performance_reports = PerformanceReport.select('*')

in views

<td><%=  @performance_reports.sum(:clicks)%></td>

basically PerformanceReport.all will load whole table and return Array of PerformanceReport you can’t chain queries on Array!!!

PerformanceReport.select('*') will return ActiveRecord::Relation and you can chain any AR method on relation

i suggest you read rails lazing loading strategy Lazy loading (will_paginate sample) and Rails Query Interface

Awesome Rails