Migrations for an Existing DB

I am writing a RoR app against a legacy Oracle database against which
other applications are running. My app will use some existing tables
and will add some. My question is how to handle this and still use
migrations. I obviously never want to run rake db:migrate against the
production db and have it delete any tables that are being used by
other apps (though I wouldn’t mind being able to recreate these in
dev/
test), so do I, but would like to use migrations to update the
production db with the new tables.

  1. Create a test and development database that are copies of
    production as my Version 0
  2. Create migrations only for the new tables

?

Also, can I use db:schema:dump to get a copy of my production schema
to use for dev/test? If so, I’m not clear what the steps are to do
this.

Appreciate any help - thanks.

On Sep 10, 2007, at 2:58 PM, sydneyos wrote:

  1. Create a test and development database that are copies of
    production as my Version 0
  2. Create migrations only for the new tables

?

Also, can I use db:schema:dump to get a copy of my production schema
to use for dev/test? If so, I’m not clear what the steps are to do
this.

Appreciate any help - thanks.

This isn’t a full solution, but some tips based on having to
reconstruct migrations on a project where the original developers
didn’t consistently use migrations (since I’ve not had to deal [yet]
with a true legacy db in Rails).

put the legacy schema (I don’t know if you can just point your
database.yml at production and db:schema:dump) into your migration 1:
db/migrate/001_legacy_schema.rb

(I think there’s a :force=>false on the create table that might help,
too)

Put the down migration as:
def self.down
raise IrreversibleMigration, “Can’t erase Legacy schema”
end

Manually, create the schema_information table in production and set
the version column of the only row to be 1.

-Rob

Rob B. http://agileconsultingllc.com
[email protected]

Thanks Rob - that’s helpful.

On Sep 10, 2007, at 5:25 PM, sydneyos wrote:

So, if I run rake on production with the version = 1 then only
migrations numbered higher will be run, is that the idea?

Right, only the migrations numbered from (select version from
schema_information)+1 up to the highest prefix in db/migrate/*.rb
will be run. So 001_legacy_schema.rb would exist more as
documentation than anything else and the IrreversibleMigration keeps
the Migrator from ever going from 1 back to 0 (which is usually an
empty schema (with the possible exception of the schema_information
table itself that the migration creates and maintains).

-Rob

Rob B. http://agileconsultingllc.com
[email protected]

So, if I run rake on production with the version = 1 then only
migrations numbered higher will be run, is that the idea?

Thanks

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