Schema Migrations Table

Question

In my Rails 4 app I would like to collapse my migration files into one large file (similar to schema.rb) as it's time to do some housekeeping but I'm not sure on how to access the table in the database that stores migration data so that when I run a migration I don't receive any errors/conflicts.

Question How can I access and delete the data in the table that stores migration data?

Have you tried copy/pasting the `schema.rb` file into a migration file? — davegson, Sep 30 '13 at 17:51
I don't have a problem creating the single migration file - but if I just change the migration files without considering the db I will get errors during a migration. — tommyd456, Sep 30 '13 at 17:53
My current understanding is that you wish to have a file that stores all your migrations, so that you can clean em up? If so, I'd suggest looping through them and writing the data to a new file. Using methods like `File` `.glob` etc... — davegson, Sep 30 '13 at 18:02
a more popular similar question here - http://stackoverflow.com/q/3343534/753705 — abhishek77in, Oct 02 '15 at 03:40

David Lowenfels · Answer 1 · 2015-02-11T04:59:13.367

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for fun, you can also manipulate these in the console by making a model class for them...

class SchemaMigration < ActiveRecord::Base; self.primary_key = :version; end

then you can do SchemaMigration.all, SchemaMigration.last.delete, etc.

Really just a substitute for using SQL, and it is very rare that you would need to mess around at this low level… generally a bad idea but cool to see how to do it :)

edited Feb 11 '15 at 04:59

answered Feb 11 '15 at 04:51

David Lowenfels

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This works - just run that code in Rails console to create a model in that console-instance. Then you can select rows from that table with .where(:version => ...) and delete references to migrations as needed. Very helpful since PGAdmin won't let you delete rows from tables that don't have a primary key specified with the gui. – JosephK May 11 '17 at 06:08
'generally'. But there are edge cases. Created a migration with a reference, adding `default: 1` where 1 did not exist. The migration halted... but the database was already altered. Said migration could not run. This saved the day and sanity cycles for me. Needless to say, this requires monkish patience and scrutiny before altering... – Jerome Aug 31 '20 at 11:31
@JosephK you can alter the schema_migrations table with psql commands. see answer below. – Jerome Aug 31 '20 at 11:34

Bergrebell · Answer 2 · 2016-10-19T12:47:47.523

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Another solution could be to access it through:

ActiveRecord::SchemaMigration

The answer given by David didn't work in my context.

edited Oct 19 '16 at 12:47

answered Apr 06 '16 at 12:47

Bergrebell

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This is so much cleaner than the defining a new model, it should really be the top answer. – Jacob Dalton Jan 15 '19 at 02:08
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I don't believe this is available in Rails 3.2, but it is the best solution for 4+. – d3vkit May 17 '19 at 22:00
This answer is much better anyway – Marco Prins Aug 18 '20 at 09:01

score 19 · Answer 3 · answered Sep 30 '13 at 18:04

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The schema_migrations table holds the revision numbers; with the last record being the most recently executed migration. You can just manipulate these records manually.

answered Sep 30 '13 at 18:04

steakchaser

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Thanks - my question is how can I access this table - do I use the console? I want to delete all the records and then create a new migration - this sound ok? – tommyd456 Sep 30 '13 at 18:12
If this does not need to be repeatable (i.e. none of this is in production yet), I would just use your db shell (psql or mysql, etc) and run a SQL query. – steakchaser Sep 30 '13 at 18:23
it's psql but never used the shell before – tommyd456 Sep 30 '13 at 18:23
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If you have a postgres role login as `sudo -u postgres psql` – steakchaser Sep 30 '13 at 18:24
Then run whatever update or delete statement you want to run. – steakchaser Sep 30 '13 at 18:25
Mark this as the answer, if you actually used this information to solve your issue. – steakchaser Oct 17 '13 at 18:42

score 10 · Answer 4 · answered Apr 26 '19 at 14:24

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to get the last version:

ActiveRecord::SchemaMigration.last.version

or all versions:

ActiveRecord::SchemaMigration.all.map(&:version)

answered Apr 26 '19 at 14:24

localhostdotdev

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score 7 · Answer 5 · answered Jan 19 '17 at 05:46

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Not sure why you want to do this but here you go:

ActiveRecord::Migrator.get_all_versions

answered Jan 19 '17 at 05:46

Agustin

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score -1 · Answer 6 · answered Aug 31 '20 at 11:44

I've had to do some cleanup of the sort: accumulation of seemingly trivial migrations create such pollution that things stop making sense.

As a last phase of development (not recommended once in production), you can clear out the schema_migrations table, consolidate your migrations (one-to-one with classes) and create a new table (beware: running migrate has different behaviours, depending on mysql vs postgresql)

@david-lowenfels answer is perfect for this context.

All this, naturally, assumes you haven't made errors in keys, indices, defaults. This is a serious task, but not an insensible one at the end of a development phase.

Schema Migrations Table

6 Answers6