Dynamic database connection in a Rails App

Question

I'm quite new to Rails but in my current assignment I have no other choice but use RoR. My problem is that in my app I would like to create, connect and destroy databases automatically on user demand but as far as I understand it is quite hard to accomplish this with ActiveRecord. It would be nice to hear some advice from more experienced RoR developers on this issue.

The problem in details: I have a main database (which I access with activerecord). In this database I store a list of my active programs (and some template data for creating new programs). I would like to create a separate database for each of this programs (when a user creates a new program in my app). In the programs' databases I would like to store the state and basic info of the particular program and a huge amount of program related data (which is used to calculate the state and is necessary to have for audit reasons). My problem is that for example I want a dashboard listing all the active programs and their state data. So first I have to get the list from my main db and after that I have to connect to all the required program databases and get the state data.

My question is what is the best practice to accomplish this? What should I use (ActiveRecord, a particular gem, etc.)?

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Hi, thanks for your answers so far, I would like to add a couple of details to make my problem more clear for you:

First of all, I'm not confusing database and table. In my case there is a tool which is processing log files. Its a legacy tool (written in ruby 1.8.6) and before running it, I have to run an SQL script which creates a database with prefilled- and also with empty tables for this tool. The tool then processes the logs and inserts the calculated data into different tables in this database. The catch is that the new system should support running programs parallel which means I have to create different databases for different programs.(this was not an issue so far while the tool was configured by hand before each run, but now the configuration must be automatic by my tool) There is no way of changing the legacy tool while it would be too complicated in the given time frame, also it's a validated tool. So this is the reason I cannot use different tables for different programs, because my solution should be based on an other tool.

Summing my task up: I have to crate a complex tool using RoR and Ruby 2.0.0 which: - creates a specific database for a legacy tool every time a user want to start a new program - configures this old tool on a daily basis to process the required logs and insert the calculated data into the appropriate database - access these databases and show dashboards based on their data

The database I'm using is MySQL.

I cannot use other framework, because the future owner of my tool won't be able to manage/change/update it. So I have to go with RoR, which is quite painful for me right now and I really hope some of you guys can give me a little guidance.

Answer 1

Ok, this is certainly outside of the typical use case scenario, BUT it is very doable within Rails and ActiveRecord.

First of all, you're going to want to execute some SQL directly, which is fine, but you'll also have to take extra care if you're using user input to determine the name of the new database for instance, and do your own escaping. (Or use one of ActiveRecord's lower-level escaping methods that we normally don't worry about.) The basic idea though is something like:

create_sql = <<SQL
CREATE TABLE foo ...
SQL
ActiveRecord::Base.connection.execute(create_sql)

Although now that I look at ActiveRecord::ConnectionAdapters::Mysql2Adapter, there's a #create method that might help you.

The next step is actually doing different things in the context of different databases. The key there is ActiveRecord::Base.establish_connection. Using that, and passing in the params for the database you just created, you should be able to do what you need to for that particular db. If the db's weren't being created dynamically, I'd put that line at the top of a standard ActiveRecord model so that that model would always connect to that db instead of the main one. If you want to use the same class, and connect it to different db's (one at a time of course), you would probably remove_connection before calling establish_connection to the next one.

I hope this points you in the right direction. Good luck!