Re: Query for cascading children to a parent
Thanks.. I think that will work.. will try it out shortly!
On Oct 8, 11:08 am, "Richard Dahl" <[EMAIL PROTECTED]> wrote:
> I have a model class 'Organization' with a parent and I do this with a
> method get_child_orgs:
>
> get_child_orgs(self):
> child_orgs = []
> co = Organization.objects.filter(parent__exact = self)
> for c in co:
> child_orgs.append(c)
> gc = c.get_child_orgs()
> child_orgs.extend(gc)
> return child_orgs
>
> On 10/8/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
>
>
>
> > Ok..thanks.. I was afraid I was going to get that answer. If I do
> > this with select_related, I'm still going to have to implement a loop
> > to display them all in one list, because they'd come back as
> > company.parent_company.parent_company etc, instead of all in one top
> > level list... right?
>
> > On Oct 8, 9:19 am, Malcolm Tredinnick <[EMAIL PROTECTED]>
> > wrote:
> > > On Mon, 2007-10-08 at 13:13 +, [EMAIL PROTECTED] wrote:
> > > > In my model class I have:
>
> > > > class Company(models.Model):
> > > > company_id = models.AutoField(primary_key=True)
> > > > parent_company = models.ForeignKey("self",null=True)
> > > > .
> > > > .
>
> > > > How would I query to get back all children companies, as well as all
> > > > of their children companies, and their children companies, etc,
> > > > without writing a nested loop to do so?
>
> > > You can't do it with a general query because there's no way to do it in
> > > SQL with this data structure. The SQL has to do a join each time you
> > > query from parent back to child (or vice-versa), so we need to know the
> > > number of joins to create a query construction time.
>
> > > There is a "depth" parameter for select_related() queries that limits
> > > the number of recursion steps (otherwise infinite loops would result for
> > > queries like this) and you could use that to control the maximum number
> > > of children. However, I believe there are some bugs with it working for
> > > small values of depth (depth=1) and there might be others, so check the
> > > results carefully.
>
> > > Regards,
> > > Malcolm
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Re: Query for cascading children to a parent
I have a model class 'Organization' with a parent and I do this with a
method get_child_orgs:
get_child_orgs(self):
child_orgs = []
co = Organization.objects.filter(parent__exact = self)
for c in co:
child_orgs.append(c)
gc = c.get_child_orgs()
child_orgs.extend(gc)
return child_orgs
On 10/8/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
>
>
> Ok..thanks.. I was afraid I was going to get that answer. If I do
> this with select_related, I'm still going to have to implement a loop
> to display them all in one list, because they'd come back as
> company.parent_company.parent_company etc, instead of all in one top
> level list... right?
>
>
> On Oct 8, 9:19 am, Malcolm Tredinnick <[EMAIL PROTECTED]>
> wrote:
> > On Mon, 2007-10-08 at 13:13 +, [EMAIL PROTECTED] wrote:
> > > In my model class I have:
> >
> > > class Company(models.Model):
> > > company_id = models.AutoField(primary_key=True)
> > > parent_company = models.ForeignKey("self",null=True)
> > > .
> > > .
> >
> > > How would I query to get back all children companies, as well as all
> > > of their children companies, and their children companies, etc,
> > > without writing a nested loop to do so?
> >
> > You can't do it with a general query because there's no way to do it in
> > SQL with this data structure. The SQL has to do a join each time you
> > query from parent back to child (or vice-versa), so we need to know the
> > number of joins to create a query construction time.
> >
> > There is a "depth" parameter for select_related() queries that limits
> > the number of recursion steps (otherwise infinite loops would result for
> > queries like this) and you could use that to control the maximum number
> > of children. However, I believe there are some bugs with it working for
> > small values of depth (depth=1) and there might be others, so check the
> > results carefully.
> >
> > Regards,
> > Malcolm
>
>
> >
>
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Re: Query for cascading children to a parent
Am Montag, 8. Oktober 2007 15:13 schrieb [EMAIL PROTECTED]:
> In my model class I have:
>
> class Company(models.Model):
> company_id = models.AutoField(primary_key=True)
> parent_company = models.ForeignKey("self",null=True)
> .
> .
>
>
> How would I query to get back all children companies, as well as all
> of their children companies, and their children companies, etc,
> without writing a nested loop to do so?
>
My models has a method like this:
def parents(self):
iloop=0
parent=self.parent
parents=[]
while parent:
iloop+=1
assert iloop<1000, "Endlosschleife"
parents.append(parent)
parent=parent.parent
return parents
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Re: Query for cascading children to a parent
On Mon, 2007-10-08 at 13:31 +, [EMAIL PROTECTED] wrote: > Ok..thanks.. I was afraid I was going to get that answer. If I do > this with select_related, I'm still going to have to implement a loop > to display them all in one list, because they'd come back as > company.parent_company.parent_company etc, instead of all in one top > level list... right? Yes. You're going to have to do that at some point. Either you construct the flattened version in Python or you do it with custom SQL (which would require a loop in an SQL procedural language in any case). There's no magical way to make the right data structure appear just with a relational query. Regards, Malcolm --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~--~~~~--~~--~--~---
Re: Query for cascading children to a parent
Ok..thanks.. I was afraid I was going to get that answer. If I do
this with select_related, I'm still going to have to implement a loop
to display them all in one list, because they'd come back as
company.parent_company.parent_company etc, instead of all in one top
level list... right?
On Oct 8, 9:19 am, Malcolm Tredinnick <[EMAIL PROTECTED]>
wrote:
> On Mon, 2007-10-08 at 13:13 +, [EMAIL PROTECTED] wrote:
> > In my model class I have:
>
> > class Company(models.Model):
> > company_id = models.AutoField(primary_key=True)
> > parent_company = models.ForeignKey("self",null=True)
> > .
> > .
>
> > How would I query to get back all children companies, as well as all
> > of their children companies, and their children companies, etc,
> > without writing a nested loop to do so?
>
> You can't do it with a general query because there's no way to do it in
> SQL with this data structure. The SQL has to do a join each time you
> query from parent back to child (or vice-versa), so we need to know the
> number of joins to create a query construction time.
>
> There is a "depth" parameter for select_related() queries that limits
> the number of recursion steps (otherwise infinite loops would result for
> queries like this) and you could use that to control the maximum number
> of children. However, I believe there are some bugs with it working for
> small values of depth (depth=1) and there might be others, so check the
> results carefully.
>
> Regards,
> Malcolm
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Re: Query for cascading children to a parent
On Mon, 2007-10-08 at 13:13 +, [EMAIL PROTECTED] wrote:
> In my model class I have:
>
> class Company(models.Model):
> company_id = models.AutoField(primary_key=True)
> parent_company = models.ForeignKey("self",null=True)
> .
> .
>
>
> How would I query to get back all children companies, as well as all
> of their children companies, and their children companies, etc,
> without writing a nested loop to do so?
You can't do it with a general query because there's no way to do it in
SQL with this data structure. The SQL has to do a join each time you
query from parent back to child (or vice-versa), so we need to know the
number of joins to create a query construction time.
There is a "depth" parameter for select_related() queries that limits
the number of recursion steps (otherwise infinite loops would result for
queries like this) and you could use that to control the maximum number
of children. However, I believe there are some bugs with it working for
small values of depth (depth=1) and there might be others, so check the
results carefully.
Regards,
Malcolm
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Query for cascading children to a parent
In my model class I have:
class Company(models.Model):
company_id = models.AutoField(primary_key=True)
parent_company = models.ForeignKey("self",null=True)
.
.
How would I query to get back all children companies, as well as all
of their children companies, and their children companies, etc,
without writing a nested loop to do so?
Thanks for any info.
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