I love Rails Console. If there is anything wrong with my Rails application, I can simply fire the console, and debug from there. Rails makes the query to db very simple and elegant by providing us the ActiveRecord. However, sometimes you may want to know the underlying raw sql statement being sent to the database to see if there is any problem. Especially your rails app is being quite slow, you may want to check if this could be the problem.


So you know that under development mode, the log would print out the raw sql statements executed. What about Rails Console. By default, if you typed in any code that queries the database, it would simply return the objects back to you. You can do the following in order to show the raw sql statements:


Immediately after you have entered Rails Console, typed in the following code in console:


ActiveRecord::Base.logger = Logger.new(STDOUT)

After that, it should print out the sql queries.

If you expect a database table to grow very large, then you will often create some index on the columns that are used to be searched quite often. E.g. if you have a user table, usually you will create index on the user_id column, as usually you will query the table to check if a user_id exists in database. The benefit of using an index for database table is quite true when the table is large although it has some disadvantage as well, like slower update/new record operation due to the needs to update the index file and it takes up extra disk space as well.

 

If no index exists on a table, a table scan must be performed for each table referenced in a database query. The larger the table, the longer a table scan takes because a table scan requires each table row to be accessed sequentially. Although a table scan might be more efficient for a complex query that requires most of the rows in a table, for a query that returns only some table rows an index scan can access table rows more efficiently.

 

The optimizer chooses an index scan if the index columns are referenced in the SELECT statement and if the optimizer estimates that an index scan will be faster than a table scan. Index files generally are smaller and require less time to read than an entire table, particularly as tables grow larger. In addition, the entire index may not need to be scanned. The predicates that are applied to the index reduce the number of rows to be read from the data pages. – extracts from the IBM website.

 

So when it comes to rails, how do you create index using active record migration?

In order to create database index for a certain table, you might have done the following under active record database migration file before.

def self.up
  create_table :table_names do |t|
     t.string :user_id
     t.index :user_id, :unique => true
  end
end

Although you may be able to find the index function API under rails API page.However, the index won’t be created as expected for you. The right way to create an index is using method add_index after you have created the table .

def self.up
  create_table :table_name do |t|
     t.string :user_id
  end
  add_index :table_name, :user_id, :unique => true
end

index function is only available when doing change_table call. So you can also do the following to create the index:

def self.up
   change_table :table_name do |t|
      t.index :user_id, :unique => true
   end
end

So that is to say an index can be created only when the table is created.
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Today I ran into a problem when trying to connect to mysql database to download some data using Rails 2. I install mysql using macports. After install mysql, i install mysql gem using the following command:

gem install mysql

This actually installed the latest mysql gem 2.8.1. However, when I run my project in production mode to connect to mysql I get the following error:

uninitialized constant MysqlCompat::MysqlRes

It turns out that mysql 2.8.1 driver seems to have a problem. So to fix this, you should do the following to install mysql 2.7.

export ARCHFLAGS=”-arch i386 -arch x86_64″ ;sudo gem install –no-rdoc –no-ri -v=2.7 mysql — –with-mysql-config=/opt/local/bin/mysql_config5

Do replace the mysql-config to the real configuration path in your os.

For more information do checkout the discussion at StackOverflow

I attended the red dot ruby conference in Singapore last weekend. It was south east asia’s first ruby conference and I am very glad that I can attend it. There were around 240 rubyist attended the conference. I am quite happy to see that ruby and rails developers are all quite passionate. Personally, I love developing in ruby and rails as well. It is quite enjoyable. All the codes that you have written is quite nicely organized and you can say it is quite beautiful.

 

Some of the talks were quite interesting as well like Matz – creator of ruby and Dave Thomas – an original Pragmatic Programmer. Matz gave a talk on the future of ruby. He points out that ruby community is growing fast and he is expecting 4 million users in the ruby community next year.  The following is photo that I have taken with Matz and ShareInvestor IT director Dau Hee.

Here is how you can use gmail as free SMTP server so that you can use it to send emails in rails application for free.

1. You have to install the actionmailer-tls plugin into your rails project

Gmail only support SSL SMTP mailing service. So if you can’t create a SSL connection to its SMTP server, you can’t send emails through them. This plugin is created to solve this problem.

2. Change your environment.rb

First you have to make sure the plugin is loaded. At the end of the environment.rb, put the following:

require 'smtp_tls'

3. Add mailer configuration
You can put this in environment.rb or environments/development.rb or environments/production.rb depends on which environment you want to use this mailing function.

config.action_mailer.delivery_method = :smtp
  config.action_mailer.smtp_settings = {
    :address => "smtp.gmail.com",
    :port => 587,
    :authentication => :plain,
    :domain => INSERT_MAIL_DOMAIN,
    :user_name => INSERT_MAIL_ADDRESS,
    :password => INSRT_MAIL_PASSWORD
  }

Now trying sending emails with your rails application. Now depends on your ruby version, you may see the following errors:

ERROR ArgumentError: wrong number of arguments (3 for 2)
FILE config/initializers/smtp_tls.rb, line 8

This is obvious that the function check_auth_args is expecting 2 argument, while 3 is given. So let’s fix it:

#check_auth_args user, secret, authtype if user or secret
if RUBY_VERSION > "1.8.6"
  check_auth_args user, secret # for rails 1.8.7
else
  check_auth_args user, secret, authtype if user or secret # for rails 1.8.6
end

Now you should be able to send emails, however, gmail has a 500 mails/day limit. In this case, you may set up multiple accounts, and rotate the settings when sending email error is caught.