Joins in ActiveRecord#find and least principle surprise

[Rodrigo Rosenfeld Rosas-3]

Frequently I lose some time trying to figure out why my tests are
failing when I use joins in ActiveRecord#find.

The logic seems fine, but the tests still fail. Than I remember that I
should convert the integer properties from columns of other join tables
from string to integer:

assert Model.find(:first, :select => 'models.*, other_table.integer_column',
   :joins => 'left join other_table on
other_table.model_id=models.id').integer_column*.to_i* == 1

What are the reasons that the column types are not the expected ones?
Would it be complicated to implement or would it lose performance or
just no one cared about this yet?

Thanks in advance,

Rodrigo.


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[Michael Koziarski]

> What are the reasons that the column types are not the expected ones?
> Would it be complicated to implement or would it lose performance or
> just no one cared about this yet?

It's the same with this case:

Foo.find(:select=> "*, SUM(something) as SomeFakeAttribute")

We don't know the type of those values, and have no reliable way to
figure them out.  In the event that the database driver itself does
typecasting (and some of them do) you'll get the right types
automatically.

So it's not a performance thing, we just don't have enough information
to reliably do the typecasting.  The place that does is the database
driver, and that's the place where you'd need to send a patch.


--
Cheers

Koz

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[Jeremy Evans]

On Mon, Nov 2, 2009 at 7:46 PM, Michael Koziarski <michael@...> wrote:

>
>> What are the reasons that the column types are not the expected ones?
>> Would it be complicated to implement or would it lose performance or
>> just no one cared about this yet?
>
> It's the same with this case:
>
> Foo.find(:select=> "*, SUM(something) as SomeFakeAttribute")
>
> We don't know the type of those values, and have no reliable way to
> figure them out.  In the event that the database driver itself does
> typecasting (and some of them do) you'll get the right types
> automatically.
>
> So it's not a performance thing, we just don't have enough information
> to reliably do the typecasting.  The place that does is the database
> driver, and that's the place where you'd need to send a patch.

For ruby-mysql and all three ruby postgres drivers (pg, postgres, and
postgres-pr), the driver itself returns column values as strings, but
it also gives you column type information that you can use to typecast
those strings.  Sequel uses that column type information to typecast
such values correctly.  See
http://github.com/jeremyevans/sequel/blob/master/lib/sequel/adapters/postgres.rb#L95
and http://github.com/jeremyevans/sequel/blob/master/lib/sequel/adapters/mysql.rb#L26
for an examples of conversion procs used based on the column type
number.

I'm not saying ActiveRecord should take that approach, I'm just saying
the information is there, at least for those drivers.

Jeremy

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[Michael Koziarski]

> For ruby-mysql and all three ruby postgres drivers (pg, postgres, and
> postgres-pr), the driver itself returns column values as strings, but
> it also gives you column type information that you can use to typecast
> those strings.  Sequel uses that column type information to typecast
> such values correctly.  See
> http://github.com/jeremyevans/sequel/blob/master/lib/sequel/adapters/postgres.rb#L95
> and http://github.com/jeremyevans/sequel/blob/master/lib/sequel/adapters/mysql.rb#L26
> for an examples of conversion procs used based on the column type
> number.
>
> I'm not saying ActiveRecord should take that approach, I'm just saying
> the information is there, at least for those drivers.

I stand corrected!

I believe the oracle / mssql drivers do this typecasting interally and
that still feels cleaner, however if someone wanted to take a look at
that logic and pull it into the postgres / mysql adapters we can see
what breaks / doesn't.


--
Cheers

Koz

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[Rodrigo Rosenfeld Rosas-3]

Em 03-11-2009 04:41, Michael Koziarski escreveu:

>> For ruby-mysql and all three ruby postgres drivers (pg, postgres, and
>> postgres-pr), the driver itself returns column values as strings, but
>> it also gives you column type information that you can use to typecast
>> those strings.  Sequel uses that column type information to typecast
>> such values correctly.  See
>> http://github.com/jeremyevans/sequel/blob/master/lib/sequel/adapters/postgres.rb#L95
>> and http://github.com/jeremyevans/sequel/blob/master/lib/sequel/adapters/mysql.rb#L26
>> for an examples of conversion procs used based on the column type
>> number.
>>
>> I'm not saying ActiveRecord should take that approach, I'm just saying
>> the information is there, at least for those drivers.
>>      
>
> I stand corrected!
>
> I believe the oracle / mssql drivers do this typecasting interally and
> that still feels cleaner, however if someone wanted to take a look at
> that logic and pull it into the postgres / mysql adapters we can see
> what breaks / doesn't.
>
>
>    

It happens that at this moment I'm very late on a project, but as soon I
finish it (in about 3 months), I'll take a look again on this subject.

There is already another patch I would like to send that I am
postponning: allow a further option ':full_message' in validations. It
will also have to wait...

But at least now I know there is no problem in submitting such patch.

Thank you,

Rodrigo.


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