[google-appengine] Reference properties and ordering results
Hi, Is it possible to do anything with a reference property other than cycle through the referenced objects in whatever order they are returned? For example I have a number of reference properties to instances where the creation date is crucial to how they are subsequently managed. Is there a way to order the result? class Reel(db.Model): name = db.StringProperty() class Frame(db.Model): # datetime.datetime.now() when the object is first created. auto_now_add_prop = db.DateTimeProperty(auto_now_add=True) # reference to the one and only reel this frame belong to reel = db.ReferenceProperty(Reel, collection_name='frames') I would like to order 'reel.frames' depending on the 'auto_now_add_prop' date. Is this the right way to access these instances if date order access is frequent and crucial? The Frame model will have millions of instances so a query there matching for a given Reel instance would be expensive. Ideas/advice/a thread I haven't seen? Alex -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
Re: [google-appengine] Reference properties and ordering results
Alex, You can only order by properties on the model itself. If you want to order by a property on a referenced model, you need to include it. So in your case you might want to add a reelName property to Frame, then just be sure you handle updating that property when you change the name on Reel. Robert On Wed, Feb 24, 2010 at 9:09 AM, Alex alexle...@googlemail.com wrote: Hi, Is it possible to do anything with a reference property other than cycle through the referenced objects in whatever order they are returned? For example I have a number of reference properties to instances where the creation date is crucial to how they are subsequently managed. Is there a way to order the result? class Reel(db.Model): name = db.StringProperty() class Frame(db.Model): # datetime.datetime.now() when the object is first created. auto_now_add_prop = db.DateTimeProperty(auto_now_add=True) # reference to the one and only reel this frame belong to reel = db.ReferenceProperty(Reel, collection_name='frames') I would like to order 'reel.frames' depending on the 'auto_now_add_prop' date. Is this the right way to access these instances if date order access is frequent and crucial? The Frame model will have millions of instances so a query there matching for a given Reel instance would be expensive. Ideas/advice/a thread I haven't seen? Alex -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
Re: [google-appengine] Reference properties and ordering results
Brian,
I just re-read your thread more carefully. I think what you want to
know is simply:
reel_frames = reel.frames.order('auto_now_add_prop.order')
'frames' on Reel (created by the reference property from Frames) is
just a query object.
Robert
On Wed, Feb 24, 2010 at 3:01 PM, Robert Kluin robert.kl...@gmail.com wrote:
Alex,
You can only order by properties on the model itself. If you want
to order by a property on a referenced model, you need to include it.
So in your case you might want to add a reelName property to Frame,
then just be sure you handle updating that property when you change
the name on Reel.
Robert
On Wed, Feb 24, 2010 at 9:09 AM, Alex alexle...@googlemail.com wrote:
Hi,
Is it possible to do anything with a reference property other than
cycle through the referenced objects in whatever order they are
returned? For example I have a number of reference properties to
instances where the creation date is crucial to how they are
subsequently managed. Is there a way to order the result?
class Reel(db.Model):
name = db.StringProperty()
class Frame(db.Model):
# datetime.datetime.now() when the object is first created.
auto_now_add_prop = db.DateTimeProperty(auto_now_add=True)
# reference to the one and only reel this frame belong to
reel = db.ReferenceProperty(Reel, collection_name='frames')
I would like to order 'reel.frames' depending on the
'auto_now_add_prop' date. Is this the right way to access these
instances if date order access is frequent and crucial?
The Frame model will have millions of instances so a query there
matching for a given Reel instance would be expensive. Ideas/advice/a
thread I haven't seen?
Alex
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Re: [google-appengine] Reference Properties
Of course you can use id/name to instead of reference property, but you can get some benefit when using reference property. One is back reference. If a reference to b, b also reference to a, you need store a's key in b and b's key in a. But using reference property, you can automatically get a back reference. Once you need change the relationship, link a and c, you don't need change a, b, c at the same time(maybe a transaction), just change a's reference property to point to c, and everything has been done. 2009/11/29 MajorProgamming sefira...@gmail.com: I was wondering: isn't using reference properties a waste of space? Wouldn't it make more sense to store the id (assuming not using key_name) of the entity. After all, if the Kind is known, one can easily generate the full key based on that. And with a reference property it actually stores the _entire_ key (very long!). Why? -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
Re: [google-appengine] Reference Properties
I think you can acheive the back reference by defining an instance
method that returns a query object defined to search the other model
for references to itself. In fact I think that is all
ReferenceProperty does anyway.
Try something like this:
class ModelA(db.Model):
def modelB_list(self):
if self.key():
refs = ModelB.all()
refs.filter('a_id_ref =', self.key().id())
return refs
return None
class ModelB(db.Model):
a_ref_id = db.IntegerProperty()
ma = ModelA()
ma.put()
mb1 = ModelB(a_id_ref=ma.key())
mb2 = ModelB(a_id_ref=ma.key())
db.put([mb1,mb2])
for mb in ma.modelB_list:
print str(mb.key())
Robert
On Nov 29, 2009, at 5:17, 风笑雪 kea...@gmail.com wrote:
Of course you can use id/name to instead of reference property, but
you can get some benefit when using reference property.
One is back reference. If a reference to b, b also reference to a, you
need store a's key in b and b's key in a.
But using reference property, you can automatically get a back
reference.
Once you need change the relationship, link a and c, you don't need
change a, b, c at the same time(maybe a transaction), just change a's
reference property to point to c, and everything has been done.
2009/11/29 MajorProgamming sefira...@gmail.com:
I was wondering: isn't using reference properties a waste of space?
Wouldn't it make more sense to store the id (assuming not using
key_name) of the entity. After all, if the Kind is known, one can
easily generate the full key based on that. And with a reference
property it actually stores the _entire_ key (very long!).
Why?
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Re: [google-appengine] Reference Properties
On Sun, Nov 29, 2009 at 5:49 PM, Robert Kluin robert.kl...@gmail.com wrote:
I think you can acheive the back reference by defining an instance
method that returns a query object defined to search the other model
for references to itself. In fact I think that is all
ReferenceProperty does anyway.
Try something like this:
class ModelA(db.Model):
def modelB_list(self):
if self.key():
refs = ModelB.all()
refs.filter('a_id_ref =', self.key().id())
return refs
return None
class ModelB(db.Model):
a_ref_id = db.IntegerProperty()
ma = ModelA()
ma.put()
mb1 = ModelB(a_id_ref=ma.key())
mb2 = ModelB(a_id_ref=ma.key())
db.put([mb1,mb2])
for mb in ma.modelB_list:
print str(mb.key())
Robert
i too use record.key().id() getting ok results empirically, blogged
how for dirty sitemap generator example (months b4 Agent Johnson did
it)
http://niklasro.blogspot.com/2009/08/sitemapxmlgz-generator.html
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Re: [google-appengine] Reference Properties
On Sat, Nov 28, 2009 at 10:09 PM, MajorProgamming wrote: I was wondering: isn't using reference properties a waste of space? Wouldn't it make more sense to store the id (assuming not using key_name) of the entity. After all, if the Kind is known, one can easily generate the full key based on that. And with a reference property it actually stores the _entire_ key (very long!). Storing the key or the full path is the only way to retrieve *any* entity. Why? Because you can't generate a full key for an entity that has ancestors using only a key name or id. You need the full path of ancestor entities. The key is the full path encoded. For simple and common cases (entity with no ancestor), you can surely store simply the id or key name. But you have to keep in mind that this won't work for any possible entity (if you store an entity with ancestor, you can't retrieve it back). -- rodrigo -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
Re: [google-appengine] Reference Properties
On Sun, Nov 29, 2009 at 9:00 PM, Rodrigo Moraes rodrigo.mor...@gmail.com wrote: On Sat, Nov 28, 2009 at 10:09 PM, MajorProgamming wrote: I was wondering: isn't using reference properties a waste of space? Wouldn't it make more sense to store the id (assuming not using key_name) of the entity. After all, if the Kind is known, one can easily generate the full key based on that. And with a reference property it actually stores the _entire_ key (very long!). Storing the key or the full path is the only way to retrieve *any* entity. Why? Because you can't generate a full key for an entity that has ancestors using only a key name or id. You need the full path of ancestor entities. The key is the full path encoded. For simple and common cases (entity with no ancestor), you can surely store simply the id or key name. But you have to keep in mind that this won't work for any possible entity (if you store an entity with ancestor, you can't retrieve it back). -- rodrigo Ancestor pattern I avoid til either understood or forced there. Same with keys, the less machinegenerated and more natural, intrinsic and geniune identificators, the better. Welcomed proven wrong or supported since still learning. Nick Rosencrantz -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
[google-appengine] Reference Properties
I was wondering: isn't using reference properties a waste of space? Wouldn't it make more sense to store the id (assuming not using key_name) of the entity. After all, if the Kind is known, one can easily generate the full key based on that. And with a reference property it actually stores the _entire_ key (very long!). Why? -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
Re: [google-appengine] Reference Properties
On Sun, Nov 29, 2009 at 12:09 AM, MajorProgamming sefira...@gmail.com wrote: I was wondering: isn't using reference properties a waste of space? Wouldn't it make more sense to store the id (assuming not using key_name) of the entity. After all, if the Kind is known, one can easily generate the full key based on that. And with a reference property it actually stores the _entire_ key (very long!). Why? We do waste space to quicken dev time and rapid prototyping. I call it a tradeoff, know ways to easy storage use several halves that view won't react to, making 100 created object 50 and 25 etc, priotitizing security, stability and views top, optimizations last. -- You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appeng...@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
[google-appengine] Reference Properties in GQL Queries
Is there any way to give a WHERE conditional values from a reference property? Something to this affect SELECT * FROM some_table WHERE referenceprop.name='yay' Where 'name' is a property of the referenced Kind? --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups Google App Engine group. To post to this group, send email to google-appengine@googlegroups.com To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en -~--~~~~--~~--~--~---
