Question

I have a ruby script that is using ActiveRecord (2.3.12) to access a MySQL database. The flow goes something like, “read database values from a config file”, “connect to database”, “Create table A if it doesn’t exist”, “download and parse a file”, “save parsed records to A“.

The code looks like the following:

ActiveRecord::Base.establish_connection(
  :adapter => 'mysql',
  :database => database_name,
  :username => username,
  :password => password,
  :host => "localhost",
  :port => 3306
)

  ...

ActiveRecord::Schema.define do
  create_table a, :force => true do |t|
    t.string :last_name, :limit => 60, :default => "", :null => false
    t.string :first_name, :limit => 30, :default => "", :null => false
    t.string :middle_initial, :limit => 2, :default => ""
    t.string :dob, :limit => 12, :default => "", :null => false
  end
end unless A.table_exists?

However, if I put incorrect DB credentials, or a non-existent database name into the establish_connection method, the script doesn’t seem to give any errors or throw any exceptions until I actually try to perform some operation on the database (i.e., create table A). I tried a begin-rescue-end around establish_connection, but it never went into the rescue block.

Why does establish_connection seem to not really…well…establish the connection? And for the life of me, I can’t figure out what it is even supposed to return. The docs HERE sure don’t seem to be any help.

Or am I doing something wrong? Please help!

Answer 1

I usually use ActiveRecord::Base.connection.active? statement to check the whether the ActiveRecord is really connected to database.

def establish_database_connection
  begin
    ActiveRecord::Base.establish_connection config["database"]
    ActiveRecord::Base.connection.active?
    logger.info "Connected to Database"
  rescue Exception => e
    logger.error "Exception db connection :  #{e.message} "
    raise "Database connection failed"
  end
end

Without ActiveRecord::Base.connection.active? statement the above code won’t raise any error on invalid credentials.