Re: View for getting field based on value from another field

Thank you!

kl. 20:48:27 UTC+2 torsdag 18. oktober 2012 skrev Dennis Lee Bieber følgende:

On Thu, 18 Oct 2012 03:03:17 -0700 (PDT), Tomas Jacobsen
<po...@tomasjacobsen.com> declaimed the following in
gmane.comp.python.django.user:

> Hello!
>
> I have a account model, which can store up to six max_values . Those
> max_values ranges from 0 to 500 000. Each max_value field has a correlating
> percentage_value field.
>
> Im trying to write a view that finds what max_value field has a value from
> 0 to 50000, and what number field it has, so I cant get the correct
> percentage_value field.
>
> My model.py:
>
> class Account(models.Model):
>     name = models.CharField(max_length=500)
>     max_value_1 = models.BigIntegerField(max_length=20, null=True,
> blank=True)
>     max_value_2 = models.BigIntegerField(max_length=20, null=True,
> blank=True)
>     max_value_3 = models.BigIntegerField(max_length=20, null=True,
> blank=True)
>     max_value_4 = models.BigIntegerField(max_length=20, null=True,
> blank=True)
>     max_value_5 = models.BigIntegerField(max_length=20, null=True,
> blank=True)
>     max_value_6 = models.BigIntegerField(max_length=20, null=True,
> blank=True)
>     percentage_1 = models.DecimalField(max_digits=8, decimal_places=3,
> null=True, blank=True)
>     percentage_2 = models.IntegerField(max_digits=8, decimal_places=3,
> null=True, blank=True)
>     percentage_3 = models.IntegerField(max_digits=8, decimal_places=3,
> null=True, blank=True)
>     percentage_4 = models.IntegerField(max_digits=8, decimal_places=3,
> null=True, blank=True)
>     percentage_5 = models.IntegerField(max_digits=8, decimal_places=3,
> null=True, blank=True)
>     percentage_6 = models.IntegerField(max_digits=8, decimal_places=3,
> null=True, blank=True)
>
        <shudder>

1)        That is a very non-normalized schema.
2)        What is "percentage" based upon? Is it

        max/sum(all max)

        It sure looks like it should be a computed field, not something
stored in the database itself.

        In raw pseudo-SQL I'd look at this as

create table Account
(
        ID        integer auto-increment primary key not null,
        Name varchar(500) not null
)

create table AccountMax
(
        ID integer auto-increment primary key not null,
        AccountID integer foreign key references Account(ID),
        position integer not null,
        maxValue bigint not null
)

with selection being something like

select a.Name, am.position, am.maxValue,
                am.maxValue / sum(am.maxValue) as "percentage"
from Account as a inner join AccountMax as am
        on a.ID = am.AccountID
group by a.Name
        having am.maxValue < 50000

(remember, that is untested pseudo-code.

--
        Wulfraed                 Dennis Lee Bieber         AF6VN
        wlf...@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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