# Migrations: getting SQL output only? **URL:** \ **Category:** Rails\ **Created:** [August 30, 2006, 10:04pm UTC](https://www.ruby-forum.com/t/migrations-getting-sql-output-only/67010 "2006-08-30T22:04:46Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![dandante](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9fc29f/32.png) [@dandante](https://www.ruby-forum.com/u/dandante)\ **Post date:** [August 30, 2006, 10:04pm UTC](https://www.ruby-forum.com/t/migrations-getting-sql-output-only/67010/1 "2006-08-30T22:04:46Z")
Is there a way to generate the SQL that would be run for a given “rake migrate” command without running the migration itself? I’d like to be able to do this for any variant of “rake migrate”, such as “rake migrate VERSION=XXX”. Anyone know? Thanks. ---
**Author:** ![dandante](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9fc29f/32.png) [@dandante](https://www.ruby-forum.com/u/dandante)\ **Post date:** [August 30, 2006, 11:08pm UTC](https://www.ruby-forum.com/t/migrations-getting-sql-output-only/67010/2 "2006-08-30T23:08:16Z")
Check out this… [http://www.agilewebdevelopment.com/plugins/activerecord\_io\_mode\_plugin](http://www.agilewebdevelopment.com/plugins/activerecord_io_mode_plugin) I think that should help you… Mark On 8/30/06, Dan T. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > – > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). > > > – Mark Van H. removed\_email\_address@domain.invalid [http://lotswholetime.com](http://lotswholetime.com) ---
**Author:** ![dandante](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9fc29f/32.png) [@dandante](https://www.ruby-forum.com/u/dandante)\ **Post date:** [August 31, 2006, 12:14am UTC](https://www.ruby-forum.com/t/migrations-getting-sql-output-only/67010/3 "2006-08-31T00:14:07Z")
Mark Van H. wrote: > Check out this… > > [http://www.agilewebdevelopment.com/plugins/activerecord\_io\_mode\_plugin](http://www.agilewebdevelopment.com/plugins/activerecord_io_mode_plugin) > > I think that should help you… This looks like it is generally useful in certain cases, but would probably be very difficult to implement for my needs. If I understand the little synopsis correctly, I would have to modify every call to an activerecord object that generates a database query. Again, what I want to do is be able to generate the SQL that would be run in a migration, without actually running the migration against the database. So if I were to use this plugin in this case, it would mean majorly hacking all the migration code in Rails, and then having to do it again whenever I upgrade Rails. I am still wondering if there is an easier way. And if not, perhaps I’d like to propose this as a feature request (how does one do that, anyway?). Here is why I want this feature: Migrations appear to me to be the best solution so far for tracking changes to schemata and data. It seems to me there is no reason why migrations can’t be used in non-rails projects. Just create a rails app, edit database.yml, start generating migrations and check them into version control along with your java, php, perl, etc. code. That’s great as far as it goes, but what about running the migrations on production? Where I work, we deploy web applications to servers run by many different ISPs. Some are Windows boxes, some are Linux. There is no guarantee that ruby/rails will be installed on any of these boxes, and no guarantee that we can prevail upon the ISPs to do so. So it seems like it would be great to be able to capture the SQL generated by “rake migrate” and then run that SQL on another machine. Obviously one would have to be careful that the migration level on one’s development machine matches the level on the target production server. I am aware that the Agile book (2nd ed) warns against running migrations against production databases. I understand the risks. Unfortunately the book is pretty vague on how you _are_ supposed to do this. It seems that using anything other than migrations causes you to lose the benefits of migrations. My scenario for running migrations on production is to first copy the production database and run the migrations against that copy, and test to make sure nothing is broken. Then backup the production db and run the migrations against it. Sorry to be long-winded, but I thought it would be beneficial to discuss my particular need. Using rails migrations in non-rails projects is something that could raise the profile of rails in those communities and ultimately perhaps gain some more converts. Plus it allows non-rails developers to reap the benefits of migrations. ---
**Author:** ![dandante](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9fc29f/32.png) [@dandante](https://www.ruby-forum.com/u/dandante)\ **Post date:** [August 31, 2006, 9:33am UTC](https://www.ruby-forum.com/t/migrations-getting-sql-output-only/67010/4 "2006-08-31T09:33:10Z")
On 30/08/06, Dan T. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Migrations appear to me to be the best solution so far for tracking > changes to schemata and data. It seems to me there is no reason why > migrations can’t be used in non-rails projects. Just create a rails app, > edit database.yml, start generating migrations and check them into > version control along with your java, php, perl, etc. code. Not entirely what you’re asking for, but I’m about to write a rails backend ui to manage a database used by a mod\_perl frontend. mod\_perl relies on a load of constraints, grants, etc that are hard to capture with migrations. I found Robbys page on using raw SQL in migrations to be a good match for what I need: [http://www.robbyonrails.com:8680/articles/2005/11/11/rails-migrations-and-postgresql-constraints](http://www.robbyonrails.com:8680/articles/2005/11/11/rails-migrations-and-postgresql-constraints) You’d still need ruby and activerecord, but that’s not a big deal in my case. – Rasputin :: Jack of All Trades - Master of Nuns [http://number9.hellooperator.net/](http://number9.hellooperator.net/) ---
**Author:** ![dandante](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9fc29f/32.png) [@dandante](https://www.ruby-forum.com/u/dandante)\ **Post date:** [August 31, 2006, 1:46am UTC](https://www.ruby-forum.com/t/migrations-getting-sql-output-only/67010/5 "2006-08-31T01:46:37Z")
> This looks like it is generally useful in certain cases, but would > probably be very difficult to implement for my needs. If I understand > the little synopsis correctly, I would have to modify every call to an > activerecord object that generates a database query. Not true, all you need to do is… output\_sql = [] ActiveRecord::Base.send\_sql\_to output\_sql #do all the migrations Now the array output\_sql will have all the generated sql in it, and nothing will have hit the db. In fact, you can also make output\_sql a file instead of an array. You just need to put this at the begining of the the migrations. Let me know if you need a more concrete example and ill see what i can get together tonight. mark – Mark Van H. removed\_email\_address@domain.invalid [http://lotswholetime.com](http://lotswholetime.com)