Fwd: Reference to one of multiple tables

Sorry, forwarding to list. Overlooked the reply-all button in Gmail
interface.

2011/12/28 Petr Jakeš <[email protected]>

>
> I'm stuck at a part of my program, but I'm not sure if this is the right
>> place to ask. Excuses if it's not.
>>
>> I have a DVD object which can have different statusses, like "on loan",
>> "sold", etc... A dvd can only have 1 status at the time, but I'm confused
>> about how to link it to 1 table only so I can access the correct status
>> with dvd.status .
>>
>> Here's an example:
>>
>> class DVD(SQLObject):
>>     status = ???? # Should be sold or onloan data
>>     # ... special "dvd" data
>>
>> class Sold(SQLObject):
>>     dvd = ForeignKey('DVD')
>>     # ... special "sold" data
>>
>> class OnLoan(SQLObject):
>>     dvd = ForeignKey('DVD')
>>     # ... special "on loan" data
>>
>> Why not just one table and the sqlmeta<http://sqlobject.org/SQLObject.html#using-sqlmeta?>?
>
>
> connection = connectionForURI('sqlite:/:memory:')
>
> class DVD(SQLObject):
>     _connection = connection
>     title = StringCol(default="")
>     inShelve = BoolCol(default=True)
>     sold = BoolCol(default=False)
>     onLoan = BoolCol(default=False)
>     def _get_statuss(self):
>         if self.sold:
>             return "sold"
>         elif self.onLoan:
>             return "onLoan"
>         elif self.inShelf:
>             return "inShelf"
> DVD.createTable()
> myFirstDVD = DVD(title="Timo")
> print myFirstDVD.statuss
>
>
The statusses have all kind of information too, like price and buyer for
sold dvd's and return date for example in the loaned status.
But your example got me thinking. Is something like the following valid?
(working example)
from sqlobject import *


connection = connectionForURI('sqlite:/:memory:')

class Sold(SQLObject):
    _connection = connection

    dvd = ForeignKey('DVD')
    buyer = StringCol(default="")

class OnLoan(SQLObject):
    _connection = connection

    dvd = ForeignKey('DVD')
    returnDate = DateCol(default=None)


class DVD(SQLObject):
    _connection = connection
    title = StringCol(default="")
    inShelve = BoolCol(default=True)
    sold = SingleJoin('Sold', joinColumn='dvd')
    onLoan = SingleJoin('OnLoan', joinColumn='dvd')
    def _get_statuss(self):
        if self.inShelf:
            return
        elif self.sold is not None:
            return self.sold
        elif self.onLoan is not None:
            return self.onLoan
DVD.createTable()
Sold.createTable()
OnLoan.createTable()
myFirstDVD = DVD(title="Timo")
s = Sold(dvd=myFirstDVD)
print myFirstDVD.statuss

But then I should handle the inShelve bool value whenever self.sold or
self.onLoan are changed.

Greets and thanks,
Timo


> HTH
>
> Petr
>

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