DB queries at import time

[Thomas Guettler]

Hi,

sometimes it happens, that db queries get executed at import time (during importing the file by the interpreter).
That's waste of time a resources.

Is there a way to test how many queries get executing during import? I want some automated way to detect these db queries.

Example:

def mychoices():
for obj in MyModel.objects.all(): # this hits the db during import. That's not good.
....

class MyForm(forms.Form):
foo=forms.ChoiceField(choices=mychoices())

--
Thomas Guettler, http://www.thomas-guettler.de/
E-Mail: guettli (*) thomas-guettler + de

[Jani Tiainen]

12.4.2012 15:09, Thomas Guettler kirjoitti:
> Hi,
>
> sometimes it happens, that db queries get executed at import time
> (during importing the file by the interpreter).
> That's waste of time a resources.
>
> Is there a way to test how many queries get executing during import? I
> want some automated way to detect these db queries.
>
> Example:
>
> def mychoices():
> for obj in MyModel.objects.all(): # this hits the db during import.
> That's not good.
> ....
>
> class MyForm(forms.Form):
> foo=forms.ChoiceField(choices=mychoices())
>
>

That is because you pass parameter as a function call, so of course
function must be evaluated. So in your code reads:

Declare class attribute "foo" as a new instance of "forms.ChoiceField"
with parameter of "choices" with values returned from "mychoices".

So to get rid of that part, you can pass method or a function as a
parameter and it will be evaluated at the runtime:

class MyForm(forms.Form):
foo=forms.ChoiceField(choices=mychoices)

--

Jani Tiainen

[Thomas Guettler]

Am 12.04.2012 15:25, schrieb Jani Tiainen:
> 12.4.2012 15:09, Thomas Guettler kirjoitti:
>> Hi,
>>
>> sometimes it happens, that db queries get executed at import time
>> (during importing the file by the interpreter).
>> That's waste of time a resources.
>>
>> Is there a way to test how many queries get executing during import? I
>> want some automated way to detect these db queries.
>>
>> Example:
>>
>> def mychoices():
>> for obj in MyModel.objects.all(): # this hits the db during import.
>> That's not good.
>> ....
>>
>> class MyForm(forms.Form):
>> foo=forms.ChoiceField(choices=mychoices())
>>
>>
>
> That is because you pass parameter as a function call, so of course function must be evaluated. So in your code reads:

> ...

Yes, I know this. But I work in a team where not everybody is a django expert. I search a way to test for queries which
happen at import time.

.... django debug toolbar does some tricky wrapping of cursor.execute(). I guess this could be a solution.

Thomas

[Daniel Roseman]

On Thursday, 12 April 2012 13:09:54 UTC+1, guettli wrote:

Hi,

sometimes it happens, that db queries get executed at import time (during importing the file by the interpreter).
That's waste of time a resources.

 

Why? Imports only happen the first time a process accesses a module. A process lasts for many requests.

 

Is there a way to test how many queries get executing during import? I want some automated way to detect these db queries.

Example:

def mychoices():
    for obj in MyModel.objects.all(): # this hits the db during import. That's not good.
        ....

class MyForm(forms.Form):
     foo=forms.ChoiceField(choices=mychoices())

The problem caused by this being executed at import time is not a "waste of time and resources", but the fact that if you add objects to MyModel, they won't appear in the MyForm.foo choices, until the process is restarted - which could be several days.

--

DR.

[Matt Schinckel]

If you install django-devserver, and enable SQL queries in the console, then

every query will be displayed as it happens, and you should be able to track them

down.

Matt.

[Thomas Guettler]

thank you, django-devserver seems to have a lot of other nice debugging features.

Thomas