Why is rake throwing this Rails migration error?

Question

I have two machines... a development machine and a production machine. When I first brought my rails app onto the production server, I had no problem. I simply imported schema.rb by running rake db:schema:load RAILS_ENV=production. All was well.

So, then on my development machine, I made some more changes and another migration, and then copy the new application over to the production machine. I then tried to update the database by running rake db:migrate RAILS_ENV=production. I get the following error: "There is already an object named 'schema_migrations' in the database."

I'm thinking to myself, ya no kidding Rake... you created it! I ran trace on rake and it seems as if rake thinks it's the first time it's ever ran. However, by analyzing my 'schema_migrations' table on my development machine and my production machine you can see that there is a difference of one migration, namely the one that I want to migrate.

I have also tried to explicitly define the version number, but that doesn't work either.

Any ideas on how I can bring my production server up to date?

Thanks!

Answer 1

This is a guess, I admit: I think that because you first ran db:schema:load instead of db:migrate in your production environment, you got the structure of your db, but not the data that migrate populates into your schema_info table. So now, when you run migrate in the production environment, there is no data in schema_info which is why migrate believes that it hasn't run yet (because it hasn't).

That said... you say that you have looked in the "schema_migrations" table, and that there is a difference of one version from dev to production... I haven't heard of that table, although I'm a few months behind on my rails version. Maybe you could try creating a "schema_info" table in the production environment, with a single "version" column, and add a row with the version that you believe your production environment to be on.

Answer 2

I would just drop the DB, add it again and run rake rb:migrate. Brad is correct that when you ran the schema load, it didn't put any records in the schema_migrations table.

This is more complicated of course if there is data you can't lose on the production server. You could get the rake backup tasks (not sure if that is part of core or not) and then run rake db:backup:write on your production database, and then after you get the migrations up to date on production, run rake db:backup:read.

Answer 3

rake db:migrate RAILS_ENV=production

Use the db:schema:load task just for the first creation, incremental changes should be migrated.

Answer 4

Let me start off by saying that I can't just 'drop' the database. It's a production server with a little over 100k records already in it. What happens if a similar problem occurs in the future? Am, I to just drop the table every time a database problem occurs? It might work this time, but it doesn't seem like a practical long term solution to every database problem. I doubt the problem I'm having now is unique to me.

1) It sounds like the 'schema_info' table and the 'schema_migrations' table are the same. In my setup, I only have 'schema_migrations'. As stated previously, the difference between the 'schema_migrations' table on the production server and the development machine is just one record. That is, the record containing the version number of the change I want to migrate.

2) From the book I read, 'Simply Rails 2', it states that when first moving to a production server, instead of running rake db:migrate, one should just run rake:db:schema:load.

3) If it matters, I'm using Rails version 2.1.

Answer 5

I'm not allowed to comment because I am not reputable, but really I'm replying to your reply.

1) I don't understand what the difference is between your production schema_migrations and the dev version. Is there a record in both tables (there should be just 1 column, "version", right) or is there a single record in the dev DB and zero records in production? If there are zero records in the production table, then do this: ActiveRecord::Base.connection.execute("INSERT schema_migrations (version) VALUES(#{my version number that production is supposedly on})")

1A) Alternatively, you could try dropping the schema_migrations table totally on production: ActiveRecord::Base.connection.execute("DROP TABLE schema_migrations") Then, re-running rake db:migrate RAILS_ENV=production. That will run migrations from starting from version 1 though, which is probably not what you're after...

1B) Alternatively alternatively, you could start an IRB session in your production environment, do either a "require" or "load" (I can never remember which, or if it matters) of the migration file that you want to load, and then call MyMigrationClass.up. You would need to manually set the version number in the schema_migrations table after that, as you would still have the problem going forward, but as a quick-fix type of hack, that would work.

Answer 6

If you do db:schema:load you will loose all your data!

Answer 7

If you get "There is already an object named 'schema_migrations' in the database." error message then I suspect that you are using MS SQLServer as your database? (As this seems like MS SQL Server error message)

If yes then which ActiveRecord database adapter you are using? (What is your database.yml file, what gems have you installed to access MS SQL Server database?)

Currently it seems that Rails does not find schema_migrations table in production schema and therefore tries to create it and this creation fails with database error message. Probably the reason is upper/lower case characters in schema_migrations table name - as far as I understand MS SQL Server identifiers are case sensitive.

Answer 8

schema_info is from an old version of Rails. schema_migrations is the new kid on the block. You should be able to remove the schema_info table as it'll no longer be used. You'll probably want to search for any issues associated with this name change.

Answer 9

rake db:schema:load will load the database structure from schema.rb. This file is the current representation of the database structure. It's used when you have an empty schema (database) that needs all the tables and indexes creating. It saves you having to run all the migrations. If you have an existing production database with data in, you don't want to run it. As others have said that would be bad!

Answer 10

hi, I also have the same problem, as Ian said

rake db:migrate RAILS_ENV=production

solved that,

thx for the help ! :D

Answer 11

Depending on the system used in production, I have seen instances where the below does not work:

rake db:migrate RAILS_ENV=production

But where this one does work:

RAILS_ENV=production rake db:migrate

Quirky, I know, but it's worth trying it to see if it makes a difference.

Answer 12

I know this post was some time ago, but I stumbled across it and it hasn't really been answered. As it comes up on google, here goes.

When you did a rake db:schema:dump (or when this was done for you by the build scripts) it will have put the definition of the migrations table into the schema.rb. At the end of the script, the process will try to create the table again, however it obviously exists already. Just remove the migrations table from the schema.rb before running rake:schema:load and there will be no error message.

You will need to set the version number in the migrations table to subsequently run migrations. So it is important to know what version your schema.rb relates too, or delete all the old migrations (they're safely in your SCM right?)