Add Excel parsing in Rails article

source/posts/2014-03-26-how-to-parse-excel-spreadsheets-in-rails.html.md

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+---
+title: How To Parse Excel Spreadsheets in Rails
+date: 2014-03-26
+author: marjinal1st
+tags: excel
+---
+
+Parsing Excel spreadsheets in Rails is a quite simple task with the gem called Roo. Let’s do it step by step.
+
+First off, you must include Roo gem in your Gemfile and install it:
+
+```ruby
+gem ‘roo’, ‘~> 1.13.2’
+```
+
+```bash
+bundle install
+```
+
+Opening an Excel spreadsheet is deadly simple:
+
+```ruby
+file = Roo::Excel.new(file_path)
+#or
+file = Roo::Excelx.new(file_path)
+```
+
+This file instance has rows in itself. You can access them with row numbers:
+
+```ruby
+file.row(1) # Gives first row
+file.row(2) # Gives second row
+```
+
+Also you can access row numbers for the first and last:
+
+```ruby
+file.first_row # Gives first row’s number, usually it’s 1
+file.last_row  # Gives last row’s number
+```
+
+Each row is an array, so you can access with index, like:
+
+```ruby
+file.row(1)[0] # Gives the first value in the first row
+file.row(1)[1] # Gives the second value in the first row
+```
+
+Now I would like to show a real life example with model relations. Let’s suppose we have a list which has many nodes. We are going to parse values from Excel spreadsheet and create nodes with these values which belongs to a list. Let’s take a look at models:
+
+```ruby
+class List  < ActiveRecord::Base
+  has_many :nodes
+end
+
+class Node < ActiveRecord::Base
+  belongs_to :list
+end
+```
+
+Now we must add a method to List model in order to parse our spreadsheet:
+
+```ruby
+class List < ActiveRecord::Base
+  has_many :nodes
+
+  def parse(file_path)
+    file = Roo::Excel.new(file_path)
+
+    (1..file.last_row).each do |i|
+      row = file.row(i)
+      node = self.nodes.new(attribute1: row[0], attribute2: row[1]) # Depends on your needs
+      node.save! if node.valid? # Make sure to use validations
+    end
+  end
+end
+```
+
+You can also use Paperclip attachment to get file, like **self.attachment**. And it’s better if you use opening handler to support different types of Excel spreadsheets.
+
+```ruby
+def open_file(file)
+  case File.extname(file.original_filename)
+    when ‘.xls’ then Roo::Excel.new(file.path)
+    when ‘.xlsx’ then Roo::Excelx.new(file.path)
+
+    else raise "Unknown file type: #{file.original_filename}"
+  end
+end
+```
+
+Now use it in the parser method:
+
+```ruby
+def parse(file_path)
+  file = open_file(file_path)
+  …
+  …
+end
+```
+
+Last of all you might want to put **open_file** method under private. Now it's up to you when to use parser method. You can use it in basic model callbacks or observers.