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Multiple has_many relations with the same class
19 February 2010 at 12:00am
I am trying to set up the following relation, but I am doubtful as to whether it is going to work:
class AvailabilityPage extends SiteTree {
static $has_many = array(
"HighSeasonIntervals" => "DateInterval",
"FullyBookedIntervals" => "DateInterval"
);
}class DateInterval extends DataObject {
static $db = array(
"StartDate" => "Date",
"EndDate" => "Date"
);
static $has_one = array(
"AvailabilityPage" => "AvailabilityPage"
);
}The resulting database schema does not seem to distinguish between a DateInterval belonging either to the HighSeasonIntervals set on AvailabilityPage, or to the FullyBookedIntervals set. Does anyone know whether or not this is going to work?
If (as I suspect), it is not going to work directly, could anyone give me some pointers on how to implement such a relation? There is nothing on this topic in the Silverstripe documentation, unfortunately.
Many thanks in advance!
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Re: Multiple has_many relations with the same class
19 February 2010 at 12:10am
Now that I have thought about it some more, the impossibility of the relation I described above seems like a fundamental shortcoming of relational data models in general. Since any SQL database is a relational data model, it's never going to work
I have worked around the problem in the following (OO-wise ugly) way:
class AvailabilityPage extends Page {
static $has_many = array(
"HighSeasonIntervals" => "DateInterval_1",
"FullyBookedIntervals" => "DateInterval_2"
);
}class DateInterval extends DataObject {
static $db = array(
"StartDate" => "Date",
"EndDate" => "Date"
);
}class DateInterval_1 extends DateInterval {
static $has_one = array(
"AvailabilityPage" => "AvailabilityPage"
);
}class DateInterval_2 extends DateInterval {
static $has_one = array(
"AvailabilityPage" => "AvailabilityPage"
);
}Still, of course, if anyone has a better idea, I'd be glad to hear it. This might actually be quite an interesting general issue in object/relational mapping.
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Re: Multiple has_many relations with the same class
19 February 2010 at 12:29am
Actually this issue was addressed in 2.4! See http://open.silverstripe.org/ticket/4632 for more information.
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Re: Multiple has_many relations with the same class
19 February 2010 at 12:32am
Great! Thanks for pointing that out; I'll stick with my workaround this time (since I'm using 2.3.6), but I'll keep it in mind for future reference
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Re: Multiple has_many relations with the same class
22 February 2010 at 6:58am
Hi,
in a relational database you'd use a m:n relation. But that's indeed a mess to implement...
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