Rails - Aug 2006 - add_column :default=>now() ?

How can I add a column -- using migrations -- so that its default comes 
out as either ''current_timestamp'' or
''now()''? If I use
'':default=>Time.now'' or
'':default=>''current_timestamp'''', the
timestamp
of the current actual time gets used, which is completely useless. I 
want the default to be the timestamp of when the record is actually 
created (yes, I know I can use ''created_on'' and so on,
but...).

Thanks!
Joe

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I don''t think you can do this in migrations because the database is not
that smart. But, you can do it easily in your model with before_create

before_create :set_foo_to_now

def set_foo_to_now
  self.foo = Time.now
end

Now, every time you create a record, it will set the field
''foo'' to
Time.now


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Right -- that''s what I currently do. Seems like there should be a way
to
get the string ''current_timestamp'' passed through to the
database
without it getting interpreted. Like a default value for string/text 
columns (haven''t played around with that yet).

Joe

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>
> before_create :set_foo_to_now
>
> def set_foo_to_now
>   self.foo = Time.now
> end
Also, if you use the magic column name ''created_at'', rails
will auto
timestamp your record on creation.

See also http://wiki.rubyonrails.org/rails/pages/MagicFieldNames

--
Yan
http://skwp.wordpress.com
http://planyp.us

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Joe Ruby wrote:
> (yes, I know I can use ''created_on'' and so on, but...).

Yan Pritzker wrote:
>>
>> before_create :set_foo_to_now
>>
>> def set_foo_to_now
>>   self.foo = Time.now
>> end
> 
> Also, if you use the magic column name ''created_at'',
rails will auto
> timestamp your record on creation.
> 
> See also http://wiki.rubyonrails.org/rails/pages/MagicFieldNames
> 
> --
> Yan
> http://skwp.wordpress.com
> http://planyp.us

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Joe Ruby wrote:
> Right -- that''s what I currently do. Seems like there should be a
way to
> get the string ''current_timestamp'' passed through to the
database
> without it getting interpreted. Like a default value for string/text
> columns (haven''t played around with that yet).
Joe, the problem with what you are proposing is that the default option
in your migration actually sets the default on the database column.
This default value is never interpreted by ruby after you run migrate
-- it exists in the database table definition itself. I don''t know of
any database that allows for a dynamic default value as you are
proposing. I''m most familiar with MySQL ... maybe you can set the
default to the MySQL function NOW() ... but I don''t know if that would
work, and it ceratinly wouldn''t work if you ever deployed your app on
another database type. Try it, I''d be interested to see how it works.

I''m pretty sure that the best way to do this is with before_create or
magic columns as was already said.


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Nate Clark wrote:
> Joe Ruby wrote:
>> Right -- that''s what I currently do. Seems like there should
be a way to
>> get the string ''current_timestamp'' passed through to
the database
>> without it getting interpreted. Like a default value for string/text
>> columns (haven''t played around with that yet).
> 
> Joe, the problem with what you are proposing is that the default option
> in your migration actually sets the default on the database column.
> This default value is never interpreted by ruby after you run migrate
> -- it exists in the database table definition itself. I don''t know
of
> any database that allows for a dynamic default value as you are
> proposing. I''m most familiar with MySQL ... maybe you can set the
> default to the MySQL function NOW() ... but I don''t know if that
would
> work, and it ceratinly wouldn''t work if you ever deployed your app
on
> another database type. Try it, I''d be interested to see how it
works.
Yep, I know how defaults in migrations work (except of course for 
sticking current_timestamp in the db unchanged).

I''m certain I used now() with mysql. I think PostgreSQL allows the use 
of any function (like user-created ones), and I KNOW now(), 
current_timestamp, and others work.

Joe

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> Joe Ruby wrote:
>> Right -- that''s what I currently do. Seems like there should
be a way to
>> get the string ''current_timestamp'' passed through to
the database
>> without it getting interpreted. Like a default value for string/text
>> columns (haven''t played around with that yet).
>
> Joe, the problem with what you are proposing is that the default option
> in your migration actually sets the default on the database column.
> This default value is never interpreted by ruby after you run migrate
> -- it exists in the database table definition itself. I don''t know
of
> any database that allows for a dynamic default value as you are
> proposing.
Postgresql does it...

test=# create table foo (str varchar(32), ts timestamp default
current_timestamp);
CREATE TABLE
test=# \d foo
                   Table "public.foo"
  Column |            Type             |   Modifiers
--------+-----------------------------+---------------
  str    | character varying(32)       |
  ts     | timestamp without time zone | default now()

test=# insert into foo (str) values (''One'');
INSERT 0 1
test=# insert into foo (str) values (''Two'');
INSERT 0 1
test=# select * from foo;
  str |             ts
-----+----------------------------
  One | 2006-08-23 18:28:24.819711
  Two | 2006-08-23 18:28:31.61082
(2 rows)


I''m most familiar with MySQL ... maybe you can set
the
> default to the MySQL function NOW() ... but I don''t know if that
would
> work, and it ceratinly wouldn''t work if you ever deployed your app
on
> another database type. Try it, I''d be interested to see how it
works.
>
> I''m pretty sure that the best way to do this is with before_create
or
> magic columns as was already said.
>
>
> >
>
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