Rails Migrations: Check Existence and Keep Going?

user_8047 0
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I was doing this kind of thing in my migrations:

add_column :statuses, :hold_reason, :string rescue puts "column already added"

but it turns out that, while this works for SQLite, it does not work for PostgreSQL. It seems like if the add_column blows up, even if the Exception is caught, the transaction is dead and so the Migration can't do any additional work.

Is there any non-DB sepecific ways to check if a column or table already exist? Failing that, is there any way to get my rescue block to really work?

migration ruby-on-rails
5 Answers
user_48897560

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

columns("[table-name]").index {|col| col.name == "[column-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 }

(this answer first posted on How to write conditional migrations in rails?)

user_5077210
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