# Rails migrations - enhanced usage

**URL:** <https://www.ruby-forum.com/t/rails-migrations-enhanced-usage/93439>\
**Category:** Rails\
**Created:** [April 3, 2006, 10:42am UTC](https://www.ruby-forum.com/t/rails-migrations-enhanced-usage/93439 "2006-04-03T10:42:24Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![surendra\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ad7895/32.png) [@surendra\_s](https://www.ruby-forum.com/u/surendra_s)\
**Post date:** [April 3, 2006, 10:42am UTC](https://www.ruby-forum.com/t/rails-migrations-enhanced-usage/93439/1 "2006-04-03T10:42:24Z")

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Hello,  
When I am writing rails migrations, quite often I make mistake in them  
which  
causes the migration tasks to stop halfway with error.

This causes lots of problem, because it results in half of the things in  
migrations changed and other half not. Also, as the schema number is  
changed,  
so things cannot be rolled back.

Is there any way to make the entire migration action atomic, i.e.,  
everything  
or none at all?

Also, while dropping tables how can I determine whether a particular  
table  
exists in the database?

Thanks.

–  
Surendra S.  
[http://ssinghi.kreeti.com](http://ssinghi.kreeti.com), [http://www.kreeti.com](http://www.kreeti.com)  
Read my blog at: [http://cuttingtheredtape.blogspot.com/](http://cuttingtheredtape.blogspot.com/)  
,----  
| “War is Peace! Freedom is Slavery! Ignorance is Strength!”  
| – Orwell, 1984, 1948  
`----

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<div class="post-metadata">

**Author:** ![surendra\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ad7895/32.png) [@surendra\_s](https://www.ruby-forum.com/u/surendra_s)\
**Post date:** [April 3, 2006, 10:54am UTC](https://www.ruby-forum.com/t/rails-migrations-enhanced-usage/93439/2 "2006-04-03T10:54:35Z")

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Surendra S. wrote:

> Also, while dropping tables how can I determine whether a particular table  
> exists in the database?
> 
> Thanks.

I’ve had this problem as well and like the idea of making it atomic –  
or at least having an atomic option.

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<div class="post-metadata">

**Author:** ![surendra\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ad7895/32.png) [@surendra\_s](https://www.ruby-forum.com/u/surendra_s)\
**Post date:** [April 3, 2006, 4:08pm UTC](https://www.ruby-forum.com/t/rails-migrations-enhanced-usage/93439/3 "2006-04-03T16:08:03Z")

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Hi !

2006/4/3, Surendra S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> Hello,  
> When I am writing rails migrations, quite often I make mistake in them which  
> causes the migration tasks to stop halfway with error.

If your DB supports it, do the migration in a transaction:

def self.up  
ActiveRecord::Base.connection.transaction do  
create\_table …  
end  
end

On the other hand, make your migrations as small as possible. That  
way, there will be less things that you’ll have to manually rollback  
if something goes wrong.

Also, a trick I often use is I dump (with data) the production DB to  
development, and do the migration on the dev database. That way, I am  
at least assured that the migration can run on existing data.

Last trick: dump your dev database before doing the migration. If  
something breaks, you just reload the schema.

Hope that helps !

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<div class="post-metadata">

**Author:** ![surendra\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ad7895/32.png) [@surendra\_s](https://www.ruby-forum.com/u/surendra_s)\
**Post date:** [April 3, 2006, 7:10pm UTC](https://www.ruby-forum.com/t/rails-migrations-enhanced-usage/93439/4 "2006-04-03T19:10:03Z")

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Francois, thanks for that tip! I’d encountered the same thing and  
wasn’t sure if transactions could be used in that way.

Jeff

François Beausoleil wrote:

> Hi !
> 
> 2006/4/3, Surendra S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):
> 
> > Hello,  
> > When I am writing rails migrations, quite often I make mistake in them which  
> > causes the migration tasks to stop halfway with error.
> 
> If your DB supports it, do the migration in a transaction:
> 
> def self.up  
> ActiveRecord::Base.connection.transaction do  
> create\_table …  
> end  
> end
> 
> On the other hand, make your migrations as small as possible. That  
> way, there will be less things that you’ll have to manually rollback  
> if something goes wrong.
> 
> Also, a trick I often use is I dump (with data) the production DB to  
> development, and do the migration on the dev database. That way, I am  
> at least assured that the migration can run on existing data.
> 
> Last trick: dump your dev database before doing the migration. If  
> something breaks, you just reload the schema.
> 
> Hope that helps !

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<div class="post-metadata">

**Author:** ![surendra\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ad7895/32.png) [@surendra\_s](https://www.ruby-forum.com/u/surendra_s)\
**Post date:** [April 3, 2006, 8:10pm UTC](https://www.ruby-forum.com/t/rails-migrations-enhanced-usage/93439/5 "2006-04-03T20:10:54Z")

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> Francois, thanks for that tip! I’d encountered the same thing and  
> wasn’t sure if transactions could be used in that way.

They only can for a few databases, like pgsql and mssql, that supports  
transactions on schema changes. The rest of the databases will ignore  
this.

## So always test your migrations on a development database first and make them small.

David Heinemeier H.  
[http://www.loudthinking.com](http://www.loudthinking.com) – Broadcasting Brain  
[http://www.basecamphq.com](http://www.basecamphq.com) – Online project management  
[http://www.backpackit.com](http://www.backpackit.com) – Personal information manager  
[http://www.rubyonrails.com](http://www.rubyonrails.com) – Web-application framework

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<div class="post-metadata">

**Author:** ![surendra\_s](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/ad7895/32.png) [@surendra\_s](https://www.ruby-forum.com/u/surendra_s)\
**Post date:** [April 4, 2006, 11:58am UTC](https://www.ruby-forum.com/t/rails-migrations-enhanced-usage/93439/6 "2006-04-04T11:58:56Z")

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“Francois B.”  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

> ActiveRecord::Base.connection.transaction do  
> at least assured that the migration can run on existing data.
> 
> Last trick: dump your dev database before doing the migration. If  
> something breaks, you just reload the schema.
> 
> Hope that helps !

Sure it did.

Thanks Francois and David.

–  
Surendra S.  
[http://ssinghi.kreeti.com](http://ssinghi.kreeti.com), [http://www.kreeti.com](http://www.kreeti.com)  
Read my blog at: [http://cuttingtheredtape.blogspot.com/](http://cuttingtheredtape.blogspot.com/)  
,----  
| “War is Peace! Freedom is Slavery! Ignorance is Strength!”  
| – Orwell, 1984, 1948  
`----