I'm developing an application where it lets users to establish many number of database connections with a has-many relationship between user and connections. The connections are passive until the user manually connects each. The motive is to perform queries on them, parallely.
I don't find good tutorials related to this, can you help me with some tips on how to accomplish this ?
After researching for a bit, turns out there's a much simpler approach using ActiveRecord Connection pool.
Make sure the model record can individually connect using
obj = ActiveRecord::Base.establish_connection(...spec...)
obj.connection.exec_query("Select * from users")
# the response is in the form of ActiveResult, which allows flexible operations around the result.
Close the connection once done with the database.
References:
http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/ConnectionHandler.html
http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/ConnectionPool.html
For my application I use this gem
https://github.com/thiagopradi/octopus
have good documentation and examples.
Assuming you want to use activerecord you can go two ways:
Here an example how to use such a model, the class_name parameter is the name of the model to be used. It's from a Sinatra app but I'm sure you'll be able to adapt it for Rails. It's a backend for a ExtJs javascript app using multiple models expecting JSON as result.
# controller
%w(create read update destroy).each do |action|
[:get, :post].each do |method|
send(method, "/path/#{action}") do
response.headers['Access-Control-Allow-Origin'] = '*'
content_type :json
if params[:store]
store = Object.const_get(params[:store])
else
store = Signal
end
resp = send(action, store, params)
jsonp(resp)
end
end
end
# in helper.rb
def read (class_name, params)
params = params.symbolize_keys
default = {store: 'Signaal', limit: 10, sort: 'id', order: 'ASC', start: 0, user: '0'}
params = default.merge params
generic_data_getter(class_name, params, params[:start], params[:limit], params[:sort], params[:dir])
end
def generic_data_getter (class_name, params, start=0, limit=10, sort='id', dir='ASC')
selection = build_selection(class_name, params)
data = class_name.where(selection).offset(start).limit(limit).order("#{sort} #{dir}")
{:success => true, :totalCount => data.except(:offset, :limit, :order).count, :result => data.as_json}
end
If not or for simple predefined searches or speed you can connect and disconnect as a connection is needed. Here an example for Oracle.
require 'oci8'
CONN = OCI8.new('scheme','password','dbserver')
sql = '....'
CONN.exec(sql) {|record|puts record.join(',')}
CONN.logoff
Be aware of malicius use like code injection.
