# Problems migrating from Postgres to MySQL **URL:** \ **Category:** Rails\ **Created:** [January 31, 2006, 12:48am UTC](https://www.ruby-forum.com/t/problems-migrating-from-postgres-to-mysql/99207 "2006-01-31T00:48:52Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![dgm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/df788c/32.png) [@dgm](https://www.ruby-forum.com/u/dgm)\ **Post date:** [January 31, 2006, 12:48am UTC](https://www.ruby-forum.com/t/problems-migrating-from-postgres-to-mysql/99207/1 "2006-01-31T00:48:52Z")
Hello everyone, I’m trying to migrate a working app from Postgres to MySQL, and I’m trying to use a migration to get it done rather than alter all my database table creation scripts to MySQL syntax. I’ve done loads of work with Postgres, but am a real newbie with MySQL… I did a ‘rake db\_schema\_dump’ from my Postgres app, and got a nice looking schema file with all my tables and fields, exactly as expected. I then created a migration file, pasted the schema info into the self.up section in the schema file and made sure there were no obvious problems. So far, so good. I then did a ‘gem install mysql’, created a new MySQL database, set up a MySQL user, tweaked database.yml to point to the new MySQL database and tried a ‘rake db\_schema\_import’. Wham! Loads of warnings, ending in an ‘uninitialized constant Mysql’. I’ve confirmed that the database.yml file is OK. I then did a ‘rake db\_schema\_import --trace’; here’s what I think is the relevant section of the output: \*\* Invoke db\_schema\_import (first\_time) \*\* Invoke environment (first\_time) \*\* Execute environment \*\* Execute db\_schema\_import rake aborted! uninitialized constant Mysql /usr/lib/ruby/gems/1.8/gems/activesupport-1.2.5/lib/active\_support/dependencies.rb:200:in `const_missing' /usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/connection_adapters/mysql_adapter.rb:35:in`mysql\_connection’ /usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active\_record/connection\_adapters/abstract/connection\_specification.rb:145:in `connection_without_query_cache=' /usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/query_cache.rb:54:in`connection=’ /usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active\_record/connection\_adapters/abstract/connection\_specification.rb:106:in `retrieve_connection' /usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/connection_adapters/abstract/connection_specification.rb:20:in`connection’ /usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active\_record/migration.rb:170:in `method_missing' ./db/schema.rb:7 /usr/lib/ruby/gems/1.8/gems/activerecord-1.13.2/lib/active_record/schema.rb:43:in`define’ ./db/schema.rb:5 /usr/lib/ruby/gems/1.8/gems/activesupport-1.2.5/lib/active\_support/dependencies.rb:207:in `load' /usr/lib/ruby/gems/1.8/gems/rails-1.0.0/lib/tasks/databases.rake:27 /usr/lib/ruby/site_ruby/1.8/rake.rb:232:in`execute’ /usr/lib/ruby/site\_ruby/1.8/rake.rb:232:in `execute' /usr/lib/ruby/site_ruby/1.8/rake.rb:202:in`invoke’ /usr/lib/ruby/1.8/thread.rb:135:in `synchronize' /usr/lib/ruby/site_ruby/1.8/rake.rb:195:in`invoke’ /usr/lib/ruby/site\_ruby/1.8/rake.rb:1719:in `run' /usr/lib/ruby/site_ruby/1.8/rake.rb:1719:in`run’ /usr/bin/rake:8 I poked around in Google and found a few people have seen the ‘uninitialized constant Mysql’ error, but these always seem to be due to using old versions of Rails, gems or MySQL. I’m running the latest Rails, just updated all gems, and MySQL 5.1, so I can’t see that I’ve got any old stuff left. Has anyone got any suggestions? Thanks in advance Dave M. ---
**Author:** ![dgm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/df788c/32.png) [@dgm](https://www.ruby-forum.com/u/dgm)\ **Post date:** [February 1, 2006, 2:19am UTC](https://www.ruby-forum.com/t/problems-migrating-from-postgres-to-mysql/99207/2 "2006-02-01T02:19:21Z")
OK I think I got it sorted - it was probably due to an update that I did to (something) that had caused the wires to get crossed on the system. The box hadn’t been rebooted for nearly 4 months, and possibly a library update had crept by me unnoticed. A reboot fixed it. Regards Dave M. ---
**Author:** ![dgm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/df788c/32.png) [@dgm](https://www.ruby-forum.com/u/dgm)\ **Post date:** [February 1, 2006, 4:13am UTC](https://www.ruby-forum.com/t/problems-migrating-from-postgres-to-mysql/99207/3 "2006-02-01T04:13:46Z")
Glad to hear you got it working. Just so you know, there’s no need to copy the generated schema file into a new migration. Just leave it in db/schema.rb and do rake db\_schema\_import to create the database. It generates a schema\_info table to hold the version, so you can just do migrations normally after that. Pat ---
**Author:** ![dgm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/df788c/32.png) [@dgm](https://www.ruby-forum.com/u/dgm)\ **Post date:** [February 1, 2006, 5:38am UTC](https://www.ruby-forum.com/t/problems-migrating-from-postgres-to-mysql/99207/4 "2006-02-01T05:38:14Z")
On 1/31/06, David M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > after a while… > Yep. I had that same experience. I now run Jamis B.'s “verbose > migrations” plugin. Very handy. > [http://svn.jamisbuck.org/rails-plugins/verbose\_migrations/](http://svn.jamisbuck.org/rails-plugins/verbose_migrations/) ---
**Author:** ![dgm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/df788c/32.png) [@dgm](https://www.ruby-forum.com/u/dgm)\ **Post date:** [February 1, 2006, 4:37am UTC](https://www.ruby-forum.com/t/problems-migrating-from-postgres-to-mysql/99207/5 "2006-02-01T04:37:54Z")
Thanks Pat, Actually this was my first chance to use migrations, and it worked reasonably well - made things a lot easier. Following through the migrations video made things a lot simpler. The biggest problem I had was the lack of referential information that comes out of rake when there’s a problem with the migration code - it can be tough to spot a problem when you’re trawling through hundreds of lines of create\_table / t\_column statements that all blur together after a while… Regards Dave M. ---
**Author:** ![dgm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/df788c/32.png) [@dgm](https://www.ruby-forum.com/u/dgm)\ **Post date:** [February 1, 2006, 6:02am UTC](https://www.ruby-forum.com/t/problems-migrating-from-postgres-to-mysql/99207/6 "2006-02-01T06:02:23Z")
Ooooh, that’s nice. Now, as long as nobody tells me this was around yesterday, when I was going through migration hell, no-one’s gonna get hurt and we can all walk out of here quietly and go back to our normal lives…! Regards Dave M.