Rails 2.3.8 - What happens to a datetime field between a form being submitted and the controller rec

Rails
1

I currently have a model that simply contains one datetime field:

class CreateElectricityReadings < ActiveRecord::Migration
def self.up
create_table :clocks do |t|
t.datetime :time_keeper
t.timestamps
end
end

def self.down
drop_table :clocks
end
end

If I enter the date string “13/10/2010” into this field its showing up
in the controller as params[:clock][:time_keeper] “2010-10-13 23:00:00
UTC”. I’ve tried overloading
ActiveRecord::ConnectionAdapters::Column string_to_date(string) and
ActiveRecord::ConnectionAdapters::Column string_to_time(string) but
these seems to get hit when an object is saved not between the form
submitting and the controller receiving the params object. Where is
the mysterious 23:00:00 hours coming from? Can anyone point me to a
good piece of reference reading for how dates and times work in rails
land?

Thanks

2

voidstar wrote in post #949920:

I currently have a model that simply contains one datetime field:

class CreateElectricityReadings < ActiveRecord::Migration
def self.up
create_table :clocks do |t|
t.datetime :time_keeper
t.timestamps
end
end

def self.down
drop_table :clocks
end
end

If I enter the date string “13/10/2010” into this field its showing up
in the controller as params[:clock][:time_keeper] “2010-10-13 23:00:00
UTC”.

Then you just need to call to_s on the date with the format you want.
Do this in the controller or the view: it’s just like any other
presentation issue. Dates are not stored as strings in the DB.

I’ve tried overloading
ActiveRecord::ConnectionAdapters::Column string_to_date(string) and
ActiveRecord::ConnectionAdapters::Column string_to_time(string) but
these seems to get hit when an object is saved not between the form
submitting and the controller receiving the params object. Where is
the mysterious 23:00:00 hours coming from?

If I had to guess, I’d guess that you’re in UTC+1 (Central European
Time). So perhaps it’s storing the time as 0:00 local time, then
converting to UTC. But I could be wrong.

Can anyone point me to a
good piece of reference reading for how dates and times work in rails
land?

You’re overthinking it. Rails does some conversion when the form is
submitted to convert three form fields (day, month, year) into a Date
object for the DB, and then saves it to a date or datetime field in the
DB. In this case, you specified a datetime field in your migration, so
when Rails retrieves the record, it puts the value into a DateTime
object. If you don’t want the time, don’t use a datetime field in the
DB – or just ignore the time.

Thanks

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

3

Hey,
Thanks for the reply, I could easily write some code to discard the
time field, which is what I’ll probably do now but I’d just like to
know how rails is doing this, I guess is should go about downloading
the rails source and grok it myself.

I’m in GMT but using daylight savings.

I guess if I just reset the time members of the DateTime object its
returning to me I’m relatively insulated from errors if this
translation changes in a future release.

Thanks
Barry

4

voidstar wrote in post #950126:

Hey,
Thanks for the reply, I could easily write some code to discard the
time field, which is what I’ll probably do now

You don’t have to discard anything. Just ignore it.

Check Rails’ field types; I think if you define the field in the
migration as date instead of datetime, you will get a Date object from
the DB, not the DateTime you currently have.

but I’d just like to
know how rails is doing this, I guess is should go about downloading
the rails source and grok it myself.

You’ve already got the Rails source.

I’m in GMT but using daylight savings.

I guess if I just reset the time members of the DateTime object its
returning to me I’m relatively insulated from errors if this
translation changes in a future release.

There’s no need to reset. There’s no translation, really; Rails is
creating a DateTime object, so it needs a time value. Again, you’re
overthinking it and persuading yourself into more complex code than is
actually necessary.

Thanks
Barry

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

5

On 14 October 2010 15:52, voidstar [email protected] wrote:

If anyone else is interested here’s the code I’m using to reset the
time to midnight.

I’d suggest you use the Rails’ “.beginning_of_day” method…

http://apidock.com/rails/ActiveSupport/CoreExtensions/Date/Calculations/beginning_of_day

… possibly easier and certainly more idiomatic.

6

On Oct 14, 2010, at 10:52 AM, voidstar wrote:

Where do I have the rails source? Also do you know what file/class
handles receiving a post request from a form?

Open a new Terminal window and type gem server [and press return].
Open a new browser and visit http://0.0.0.0:8808

Each Gem you have installed will (probably) have two links next to its
name, rdoc and www. The rdoc is whatever was generated when you
installed the Gem, and the www will be whatever passes for the
developer’s Web site.

Walter

7

I need a date/time object due to domain requirements although at this
point I don’t care about the time object, I just want it to be
midnight. There are other ways for the user to enter data into this
table where the time element becomes relevant.

Where do I have the rails source? Also do you know what file/class
handles receiving a post request from a form?

If anyone else is interested here’s the code I’m using to reset the
time to midnight.

@gas_reading = @user.gas_readings.build(params[:gas_reading])

@gas_reading.start_date = @gas_reading.start_date.change(:hour =>

0, :min => 0, :second => 0) unless @gas_reading.start_date.nil?
@gas_reading.end_date = @gas_reading.end_date.change(:hour =>
0, :min => 0, :second => 0) unless @gas_reading.end_date.nil?

8

On 14 October 2010 15:52, voidstar [email protected] wrote:

I need a date/time object due to domain requirements although at this
point I don’t care about the time object, I just want it to be
midnight. There are other ways for the user to enter data into this
table where the time element becomes relevant.

My understanding of this issue (which may be flawed) is that if you
have a datetime field on a form the rails assumes the value entered is
in local time, and converts it to gmt ready to be put in the database.
I think that if, in environment.rb you put
config.time_zone = ‘UTC’
then it will assume that the value entered is already in UTC and will
not apply the timezone offset.

Colin

9

voidstar wrote in post #950166:

I need a date/time object due to domain requirements although at this
point I don’t care about the time object,

Huh? Design for what you have now, not what you might need in future.

[…]

Where do I have the rails source?

Do you really need to ask? Remember, Ruby is an interpreted language.
That means that you’ve got the source wherever the Rails gem is
installed (in vendor/rails if you’ve done that, or wherever “gem which
rails” tells you).

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

10

On 14 October 2010 19:38, voidstar [email protected] wrote:

Thanks for the replies,

beginning_of_day makes a lot more sense.

Yes Colin that’s what’s happening, I’d just like to know where exactly
the string goes from “dd/mm/yyyy” to being “yyyy-mm-dd hh:mm:ss
timezone offset” and if there’s anyway for me to control/over ride
that behaviour.

Where and how exactly are you seeing it as this string? What do you
see in the log when the form is posted?
Apologies if you have already provided that info, I have not got time
to look back in detail at the thread at this moment.

Colin

11

Thanks for the replies,

beginning_of_day makes a lot more sense.

Yes Colin that’s what’s happening, I’d just like to know where exactly
the string goes from “dd/mm/yyyy” to being “yyyy-mm-dd hh:mm:ss
timezone offset” and if there’s anyway for me to control/over ride
that behaviour.

Marnen, You’re right what we’re doing right now isn’t good and we’re
creating technical debt. As a team we’ve discussed this and given the
current requirements and priorities/time we have left, we’ve decided
to do it this way.

Also I wouldn’t have asked how to see the rails/ruby code if I knew
how. I’m coming from java land and before that c++ where I’m used to
having to grab the sources for libraries before being able to debug
them or read them.

The source seems to be scattered about in different gems on my
machine, I found doing a “git clone git://github.com/rails/rails.git
v2.3.8” was handier to have everything in one place. Any suggestions
on where to start looking for how rails accepts a post request and
builds the params object and sends it to the correct controller?

Thanks again for all the help
Barry