Archive for the 'Uncategorized' Category

Handy ActiveRecord Migration Methods

April 23rd, 2010 | Category: Development,Rails,Uncategorized

We are undergoing a massive DB schema redesign. Much of the work is just tightening up the schema through optimizing indexes, setting default boolean and integer fields, and updating NULL allowed fields. Here is a little module I wrote to save massive amounts of code.

module MigrationHelper
  def index_exists?(table, lookup)
    lookup = Hash[:columns, Array(lookup)] unless lookup.is_a?(Hash)
  def change_column_nulls(table_name, nullable, *column_names)
    column_names.each do |column_name|
      table_columns = columns(table_name) 
      column_def ={|c| == column_name.to_s}
      raise "Unknown column name #{column_name} for #{table_name}\nAvailable columns: #{table_columns.collect(&:name).to_sentence}" if column_def.empty?
      change_column table_name, column_name, column_def.first.type, :null => nullable
  def change_column_defaults(table_name, default, *column_names)
    column_names.each do |column_name|
      change_column_default table_name, column_name, default

I fond it necessary to have the index_exists? method mainly for my development purposes. When I’m optimizing tables by doing complex indexes, I often do them right on the DB first before throwing them into a migration. By having this check I can easily skip over it if it already exists. It takes the same options as add_index. You can pass table and column names, or just table and index name. Here are some usage examples:

add_index :table, :column unless index_exists?(:table, :column)
add_index :table, [:column1, :column2] unless index_exists?(:table, [:column1, :column2])
add_index :table, [:column1, :column2, :column3], :name => "some_index_name" unless index_exists?(:table, :name => "some_index_name")

The method change_column_nulls is used to mass change the NULL allowed columns for a given table. Really not much to it, but saves a lot of code over doing change_table or change_column. Here is the usage:

change_column_nulls :table, false, :column1, :column2

And lastly change_column_defaults is just a wrapper around change_column_default for mass assignment. Usage is the same as change_column_nulls passing the default values as the second argument. I thought about combining the two, but it didn’t offer very much savings.

These were tested using MySql 5. I’m not sure about the compatibility with other servers.

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RJS redirect_to params contain &

June 25th, 2009 | Category: Uncategorized

I came across this today when I added a parameter to a RJS page.redirect_to call.  It appears that prototype or rails is not properly handling the parameters when there are more than 2.  I got around it by using a defined route in the routes.rb that looks like this:

map.route_name 'controller_name/action_name/:foo_id', :controller => 'controller_name', :action => 'action_name'

I had to change the redirect_to in my RJS file from this:

page.redirect_to page_recrawl_path(:foo_id => @foo_id, :bar_id => @bar_id, :bang => true)

To this:

page.redirect_to page_recrawl_path(@foo_id, {:bar_id => @bar_id, :bang => true})
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Ruby on Rails background process: MySQL server has gone away

June 02nd, 2009 | Category: Uncategorized

Using workling and starling to handle background tasks is very nice. Check out this link for info on setting it up.  However, I encountered the error: “Mysql::Error: MySQL server has gone away” when accessing an external DB tables like users and roles.  I found that someone recommended using verify_active_connections!, however the table the connection error occurred on was a HABTM table ‘user_roles’. I found that verify_active_connections will use the scope of the model/object you invoke it on. So the final solution was to do the following:


This will make sure users, user_roles, and roles all have valid connections. This error occurred using rails 2.0.1. It may be fixed in newer versions of ActiveRecord.

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Ruby sum array values for currency

September 15th, 2008 | Category: Uncategorized

I found this handy trick to take an array built from some hash values and spit out a currency. Here is what I used it for. Inside my model, I built some test items.

def self.test_items
    [{:price => "5.50", :weight => 10, :item_description => "Test item 1"}, {:price => "7.75", :weight => 15, :item_description => "Test item 2"}, {:price => "9.95", :weight => 20, :item_description => "Test item 3"}]

I wanted to get a “Total Price” in the view, so I did the following. I created a method in my ApplicationHelper that looks like so

def total_for_cart(prices)
    number_to_currency(prices.inject(0){|sum, price| sum.to_f + price.to_f})

The above uses the Ruby inject method from the Enumerable class to simply add the float values. I’m also using the rails helper method number_to_currency for pretty formatting. Finally my view looks like this:

<p>Total: <%= total_for_cart(items.collect{|i| i[:price]}) %></p>

That simply collects the price from the items array and passes it to my helper method. Hope its helpful!

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June 18th, 2008 | Category: Uncategorized

Hello all,

I decided to move my old blog to a wordpress instance.  Mephisto just wasn’t working out for me, regardless of my love for rails.  Anyhow, I’ll slowly be moving stuff over from my old blog.  Please stay tuned.



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