How to write conditional migrations in rails?

Question

I am looking for ways to write migrations in rails that can be executed against the database many times without failing.

For instance let say I have this migration:

Answer 1

For Rails 3.X, there's the column_exists?(:table_name, :column_name) method.

For Rails 2.X, you can check the existence of columns with the following:

columns("").index {|col| col.name == ""}


...or if you're not in a migration file:

ActiveRecord::Base.connection.columns("").index {|col| col.name == ""}
If it returns nil, no such column exists. If it returns a Fixnum, then the column does exist. Naturally, you can put more selective parameters between the {...} if you want to identify a column by more than just its name, for example:
{ |col| col.name == "foo" and col.sql_type == "tinyint(1)" and col.primary == nil }

                                                        

              
                
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