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I have several dozens Rails DB migrations which were written over a year. Is there a way to aggregate them to one migration so that I will just see a full DDL statement for the database as it exists now? I just need the current snaphot without all the history of how we got to it.

Dmitry Chornyi
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3 Answers3

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It is possible, but probably not a good idea to aggregate the migrations!

Maybe ask:

  • Why do you want to do this?
  • How often do you really need to migrate all the way to VERSION=0 and then back up again?
  • Is something really broken? (if not, then don't fix it)

I've had the same problem once.. I ended up just re-ordering my migrations, because changes in the schema caused it to not correctly migrate up/down anymore. I would be hesitant to do that again.

If you have migrations which just add fields or indexes, then maybe you can combine them with the main migration for the model -- but beware that you can't reproduce old situations anymore, e.g. older DB-dumps may not be compatible with what migration number they should be compatible with -- that is probably the biggest argument against aggregating...

Technically, you can dump the schema and then load it directly - that is one way:

rake db:schema:dump

then create a single new migration with the contents of the schema dump file db/schema.rb

Here are some similar questions:

P.S.: I found it useful to stick with the old migration numbering scheme, where the migrations do not use timestamps - for me this works better (is easier to see in which order they are).

e.g. in your config/application.rb file:

config.active_record.timestamped_migrations = false
Community
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Tilo
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  • Thanks for a detailed answer. The immediate reason why I wanted it, was just to be able to conveniently see the DB schema. Since Rails prefers to do many ususal RDBMS tasks itself (e.g., referential integrity, constraints), I would like to see them in one place. – Dmitry Chornyi Oct 06 '11 at 21:19
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    `rake db:schema:dump` is what i needed. – Dmitry Chornyi Oct 06 '11 at 21:28
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You can simply load the current schema into the DB.

rake db:schema:load RAILS_ENV=[production, test, etc.]

This will take the schema.rb file's version of the schema, and load it into the DB without running individual migrations.

NOTE: if you have migrations that put data into the DB (e.g. default values, for example), that data will not be added to the DB.

If you need to load default values into your DB, that might be better done via a custom rake task, independent of migrations.

jefflunt
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You should never be using all the migrations to get a database up and running. The current schema.rb is always what the DB looks like 'presently'.

It's good practice to periodically just truncate your migrations if you have a ton of them in there. We finally did that with one of our larger applications, removing a good 50 migrations from the folder because the only thing that matters is schema.rb. Migrations are just that, a way to migrate and make changes to an existing state of the database. They should only ever have to be run once.

nzifnab
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