ActiveRecord::ConnectionNotEstablished error - ruby-on-rails

Question

I have written a rake task to update my database which I am doing by a model. I have called the function of model inside my rake task like this:
get_first_student = Student.get_first_id
I have written the model Student like following:
class Students < ActiveRecord::Base
attr_accessible :id, :roll_num :name, :class
self.table_name = 'students'
if Rails.env == "development"
CONN1 = establish_connection :adapter => "mysql2",
:database => "mydb_dev",
:username => "root",
:password => "" ,
:host => "localhost"
CONN2 = establish_connection :adapter => "mysql2",
:database => "mydb2_dev",
:username => "root",
:password => "",
:host => "1.2.3.4"
else
CONN1 = establish_connection :adapter => "mysql2",
:database => "mydb_prod",
:username => "root",
:password => "" ,
:host => "localhost"
CONN2 = establish_connection :adapter => "mysql2",
:database => "mydb2_prod",
:username => "root",
:password => "" ,
:host => "localhost"
end
def self.get_first_id
p "****"
p CONN1
p "****"
sql = %Q{SELECT MIN(id) FROM mydb.students;}
first_student_id = CONN1.connection.execute(sql).first[0]
return first_student_id
end
After running, I am getting this following output:
#<ActiveRecord::ConnectionAdapters::ConnectionPool:0x007f948c223120 #mon_owner=nil,
#mon_count=0, #mon_mutex=#<Mutex:0x007f948c2230d0>, #spec=#
<ActiveRecord::Base::ConnectionSpecification:0x007f948c2232d8 #config=
{:adapter=>"mysql2",:database=>"mydb_dev", :username=>"root", :password=>"",
:host=>"localhost"}, #adapter_method="mysql2_connection">, #reserved_connections={},
#queue=#<MonitorMixin::ConditionVariable:0x007f948c223080 #monitor=#
<ActiveRecord::ConnectionAdapters::ConnectionPool:0x007f948c223120 ...>, #cond=#
<ConditionVariable:0x007f948c223058 #waiters=[], #waiters_mutex=#
<Mutex:0x007f948c223008>>>, #timeout=5, #size=5, #connections=[],
#automatic_reconnect=false>
ActiveRecord::ConnectionNotEstablished

Answer 1

In rails, there are two different adapter for mysql server one in mysql and mysql2 gem. Check if you have mysql gem in your gemfile. If not, then open rails console, and type ActiveRecord::Base.establish_connection("mysql://your_username:yourpassword#localhost/yourdatabasename"). Have you configured your mysql server. Are you getting error in all environments?. Check it by login into mysql server using command 'mysql -u USERNAME -p' by default its root and with not password.

Answer 2

Calling establish_connection the second time has disconnected the first pool you created and that's the CONN1 you're trying to use.
Although this method returns a ConnectionPool object that you can capture and use, it's worth avoiding. ActiveRecord manages the connection pools and unless you explicitly tell it differently will assume you only want one of them active. Recently they've added some nice new ways to manage multiple databases.