Timestamp can't be saved - postgresql - ruby-on-rails

Question

I have the below code snippet:
class Foo
include DataMapper::Resource
property :id, Serial
property :timestamp, DateTime
end
I just want to convert the current time to ms:
class Time
def to_ms
(self.to_f * 1000.0).to_i
end
end
def current_time
time = Time.now
return time.to_ms
end
time = current_time # => 1352633569151
but when I am going to save the Foo with above timestamp, then it can't be saved to the database and I'm not getting any error message.
foo = Foo.new
foo.timestamp = time
foo.save
Any idea?

Answer 1

are you using a correct format for your :datetime property?
should be like:
DateTime.now.to_s
=> "2012-11-11T14:04:02+02:00"
or a "native" DateTime object, without any conversions.
DataMapper will carry to convert it to according values based on adapter used.
also, to have exceptions raised when saving items:
DataMapper::Model.raise_on_save_failure = true
that's a global setting, i.e. all models will raise exceptions.
to make only some model to behave like this:
YourModel.raise_on_save_failure = true
http://datamapper.org/docs/create_and_destroy.html
See "Raising an exception when save fails" chapter
btw, to see what's wrong with your item before saving it, use and item.valid? and item.errors
foo = Foo.new
foo.timestamp = time
if foo.valid?
foo.save
else
p foo.errors
end
I replicated your code and got following error:
#errors={:timestamp=>["Timestamp must be of type DateTime"]}
See live demo here

Answer 2

The PostgreSQL data types would be timestamp or timestamp with time zone. But that contradicts what you are doing. You take the epoch value and multiply by 1000. You'd have to save that as integer or some numeric type.
More about the handling of timestamps in Postgres in this related answer.
I would save the value as timestamp with time zone as is (no multiplication). You can always extract ms out of it if need should be.
If you need to translate the Unix epoch value back to a timestamp, use:
SELECT to_timestamp(1352633569.151);
--> timestamptz 2012-11-11 12:32:49.151+01
Just save "now"
If you actually want to save "now", i.e. the current point in time, then let Postgres do it for you. Just make sure the database server has a reliable local time - install ntp. This is generally more reliable, accurate and simple.
Set the DEFAULT of the timestamp column to now() or CURRENT_TIMESTAMP.
If you want timestamp instead of timestamptz you can still use now(), which is translated to "local" time according to the servers timezone setting. Or, to get the time for a given time zone:
now() AT ZIME ZONE 'Europe/Vienna' -- your time zone here
Or, in your particular case, since you seem to want only three fractional digits: now()::timestamp(3) or CURRENT_TIMESTAMP(3) or CURRENT_TIMESTAMP(3) AT ZIME ZONE 'Europe/Vienna'.
Or, if you define the type of the column as timestamp(3), all timestamp values are coerced to the type and rounded to 3 fractional decimal digits automatically.
So this would be all you need:
CREATE TABLE tbl (
-- other columns
,ts_column timestamp(3) DEFAULT now()
);
The value is set automatically on INSERT, you don't even have to mention the column.
If you want to update it ON UPDATE, add a TRIGGER like this:
Trigger function:
CREATE OR REPLACE FUNCTION trg_up_ts()
RETURNS trigger AS
$BODY$
BEGIN
NEW.ts_column := now();
RETURN NEW;
END
$BODY$ LANGUAGE plpgsql VOLATILE
Trigger:
CREATE TRIGGER log_up_ts
BEFORE UPDATE ON tbl
FOR EACH ROW EXECUTE PROCEDURE trg_up_ts();
Now, everything works automatically.
If that's not what you are after, #slivu's answer seems to cover the Ruby side just nicely.

Answer 3

I'm not familiar with PostgreSQL, but why are you assigning a Fixnum (time) to timestamp (which is a DateTime)? Your model must be failing to convert time to a proper DateTime value before generating the SQL.
Try foo.save!. I'm pretty sure you'll see an error, either reported from PostgreSQL, saying 1352633569151 is not a valid value for the table column, or your model will say it can't parse 1352633569151 to a valid DateTime.
foo.timestamp = Time.now or foo.timestamp = '2012-11-11 00:00:00' is something that'll work.