Rails - Dec 2008 - Is Rails "create_table" smart enough to know if a table already exists

If I run a migration and the table already exists, is rails
"create_table" smart enough to drop the table first, or should I add
something like line #1 below.
And..
if the foreign key ''fk_seats_venues'' existed, would I not need
to drop
it before dropping the table?

I am doing a bunch of experimental hacking with a couple projects so
the table might be there after I blow away schema.rb and drop the
schema table etc etc.

class CreateSeats < ActiveRecord::Migration
  def self.up
    execute "DROP TABLE IF EXISTS seats"    #1
    create_table(:seats,  :id => false) do |t|
      t.string :id, :limit => 36
      t.integer :venue_id
      t.string :name
      t.string :section
      t.string :seat_row
      t.string :seat_number
      t.string :seat_type

      t.timestamps
    end
    execute "ALTER TABLE `seats` ADD PRIMARY KEY (`id`)"

    #add a foreign key
    execute "ALTER TABLE products ADD CONSTRAINT fk_seats_venues
FOREIGN KEY (category_id) REFERENCES venues(id)"

  end

  def self.down
    #Drop foreign key
    execute "ALTER TABLE products DROP FOREIGN KEY fk_seats_venues"
    drop_table :seats
  end
end


also, is there a way to find if the foreign key exists that less
complicated than:


IF EXISTS (SELECT NULL FROM information_schema.TABLE_CONSTRAINTS
WHERE CONSTRAINT_SCHEMA = DATABASE() AND CONSTRAINT_NAME
''fk_seats_venues'') THEN
	ALTER TABLE `object` DROP FOREIGN KEY `fk_seats_venues`;
END IF;

and if not, how do I execute a multiline Sql statement?

Thanks in advance

TW Scannell
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there is an option for create_table called :force, specify it like:

create_table :posts, :force => true do |t|
...
end
-----
Ryan Bigg
Freelancer
http://frozenplague.net







On 04/12/2008, at 3:50 PM, Teedub wrote:
>
>
> If I run a migration and the table already exists, is rails
> "create_table" smart enough to drop the table first, or should I
add
> something like line #1 below.
> And..
> if the foreign key ''fk_seats_venues'' existed, would I not
need to drop
> it before dropping the table?
>
> I am doing a bunch of experimental hacking with a couple projects so
> the table might be there after I blow away schema.rb and drop the
> schema table etc etc.
>
> class CreateSeats < ActiveRecord::Migration
>  def self.up
>    execute "DROP TABLE IF EXISTS seats"    #1
>    create_table(:seats,  :id => false) do |t|
>      t.string :id, :limit => 36
>      t.integer :venue_id
>      t.string :name
>      t.string :section
>      t.string :seat_row
>      t.string :seat_number
>      t.string :seat_type
>
>      t.timestamps
>    end
>    execute "ALTER TABLE `seats` ADD PRIMARY KEY (`id`)"
>
>    #add a foreign key
>    execute "ALTER TABLE products ADD CONSTRAINT fk_seats_venues
> FOREIGN KEY (category_id) REFERENCES venues(id)"
>
>  end
>
>  def self.down
>    #Drop foreign key
>    execute "ALTER TABLE products DROP FOREIGN KEY
fk_seats_venues"
>    drop_table :seats
>  end
> end
>
>
> also, is there a way to find if the foreign key exists that less
> complicated than:
>
>
> IF EXISTS (SELECT NULL FROM information_schema.TABLE_CONSTRAINTS
> WHERE CONSTRAINT_SCHEMA = DATABASE() AND CONSTRAINT_NAME >
''fk_seats_venues'') THEN
> 	ALTER TABLE `object` DROP FOREIGN KEY `fk_seats_venues`;
> END IF;
>
> and if not, how do I execute a multiline Sql statement?
>
> Thanks in advance
>
> TW Scannell
> >

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