I am new in django. This is my django model. But when I use the Book.objects.all() command in python shell, I am getting an error.
Why?? Please help.
This answer is very late however it may prove useful to anyone that views this question.
The error you will be experiencing is:
TypeError: coercing to Unicode: need string or buffer, datetime.date found
This is because in your model you have the code:
def __unicode__(self):
return self.title + self.publication_date
The error originates from the attempt to add a datetime object self.publication_date, to a string self.title. To fix this you can change your code to cast self.publication_date to a string like so:
def __unicode__(self):
return self.title + str(self.publication_date)
To help with this further, I would suggest formatting the string representation of the Book object a little better to make it more readable.
def __unicode__(self):
return '{} - {}'.format(self.title, str(self.publication_date))
The output from this would look something like this:
>>> from test.models import Book
>>> Book.objects.all()
<QuerySet [<Book: MyBook - 2018-03-19>]>
Related
I have a google-cloud-endpoints, in the docs, I did'nt find how to write a PATCH method.
My request:
curl -XPATCH localhost:8080/_ah/api/hellogreeting/1 -d '{"message": "Hi"}'
My method handler looks like this:
from models import Greeting
from messages import GreetingMessage
#endpoints.method(ID_RESOURCE, Greeting,`
path='hellogreeting/{id}', http_method='PATCH',
name='greetings.patch')
def greetings_patch(self, request):
request.message, request.username
greeting = Greeting.get_by_id(request.id)
greeting.message = request.message # It's ok, cuz message exists in request
greeting.username = request.username # request.username is None. Writing the IF conditions in each string(checking on empty), I think it not beatifully.
greeting.put()
return GreetingMessage(message=greeting.message, username=greeting.username)
So, now in Greeting.username field will be None. And it's wrong.
Writing the IF conditions in each string(checking on empty), I think it not beatifully.
So, what is the best way for model updating partially?
I do not think there is one in Cloud Endpoints, but you can code yours easily like the example below.
You will need to decide how you want your patch to behave, in particular when it comes to attributes that are objects : should you also apply the patch on the object attribute (in which case use recursion) or should you just replace the original object attribute with the new one like in my example.
def apply_patch(origin, patch):
for name in dir( patch ):
if not name.startswith( '__' ):
setattr(origin,name,getattr(patch,name))
I am trying to make general purpose image display class which
receives two parameters,
Key, and "Column location info in entity"
from URL and return and display specified image delivered from blob.
If you know what I am doing wrong, please give me a hint.
I have datastore "item" like below,
Key | image_index | image1 | image2 | image3 |
and I am requesting image with the URL like below,
http://stackoverwlow.com/image/{key}/{image_N}
I made url handler in the main like below,
def main():
application = webapp.WSGIApplication(
[('/', MainPage),
('/image/([^/]+)/([^/]+)', imageDisplay),
], debug=True)
wsgiref.handlers.CGIHandler().run(application)
and
I made imageDisplay class like below,
from google.appengine.ext import db
from google.appengine.ext import webapp
class imageDisplay(webapp.RequestHandler):
def get(self, _key, _size):
image = db.get(_key)
self.response.headers['Content-Type'] = 'image/jpg'
self.response.out.write(image._size)
But, if I try this code, it will return following error,
global name 'image_size' is not defined
If I specify which image in the entity should be displayed, it works.
So, the data is there.
self.response.out.write(image.image3)
My question is, how to specify "_size" from obtained entity "image"?
Thank you in advance.
With best regards
You need to fetch the attribute programmatically, like this:
self.response.out.write(getattr(image, size))
Since you're addressing your values like an array, you should probably just use one, though: use a db.ListProperty(db.Blob), instead!
In Google App Engine, I make lists of referenced properties much like this:
class Referenced(BaseModel):
name = db.StringProperty()
class Thing(BaseModel):
foo_keys = db.ListProperty(db.Key)
def __getattr__(self, attrname):
if attrname == 'foos':
return Referenced.get(self.foo_keys)
else:
return BaseModel.__getattr__(self, attrname)
This way, someone can have a Thing and say thing.foos and get something legitimate out of it. The problem comes when somebody says thing.foos.append(x). This will not save the added property because the underlying list of keys remains unchanged. So I quickly wrote this solution to make it easy to append keys to a list:
class KeyBackedList(list):
def __init__(self, key_class, key_list):
list.__init__(self, key_class.get(key_list))
self.key_class = key_class
self.key_list = key_list
def append(self, value):
self.key_list.append(value.key())
list.append(self, value)
class Thing(BaseModel):
foo_keys = db.ListProperty(db.Key)
def __getattr__(self, attrname):
if attrname == 'foos':
return KeyBackedList(Thing, self.foo_keys)
else:
return BaseModel.__getattr__(self, attrname)
This is great for proof-of-concept, in that it works exactly as expected when calling append. However, I would never give this to other people, since they might mutate the list in other ways (thing[1:9] = whatevs or thing.sort()). Sure, I could go define all the __setslice__ and whatnot, but that seems to leave me open for obnoxious bugs. However, that is the best solution I can come up with.
Is there a better way to do what I am trying to do (something in the Python library perhaps)? Or am I going about this the wrong way and trying to make things too smooth?
If you want to modify things like this, you shouldn't be changing __getattr__ on the model; instead, you should write a custom Property class.
As you've observed, though, creating a workable 'ReferenceListProperty' is difficult and involved, and there are many subtle edge cases. I would recommend sticking with the list of keys, and fetching the referenced entities in your code when needed.
Currently my application caches models in memcache like this:
memcache.set("somekey", aModel)
But Nicks' post at http://blog.notdot.net/2009/9/Efficient-model-memcaching suggests that first converting it to protobuffers is a lot more efficient. But after running some tests I found out it's indeed smaller in size, but actually slower (~10%).
Do others have the same experience or am I doing something wrong?
Test results: http://1.latest.sofatest.appspot.com/?times=1000
import pickle
import time
import uuid
from google.appengine.ext import webapp
from google.appengine.ext import db
from google.appengine.ext.webapp import util
from google.appengine.datastore import entity_pb
from google.appengine.api import memcache
class Person(db.Model):
name = db.StringProperty()
times = 10000
class MainHandler(webapp.RequestHandler):
def get(self):
self.response.headers['Content-Type'] = 'text/plain'
m = Person(name='Koen Bok')
t1 = time.time()
for i in xrange(int(self.request.get('times', 1))):
key = uuid.uuid4().hex
memcache.set(key, m)
r = memcache.get(key)
self.response.out.write('Pickle took: %.2f' % (time.time() - t1))
t1 = time.time()
for i in xrange(int(self.request.get('times', 1))):
key = uuid.uuid4().hex
memcache.set(key, db.model_to_protobuf(m).Encode())
r = db.model_from_protobuf(entity_pb.EntityProto(memcache.get(key)))
self.response.out.write('Proto took: %.2f' % (time.time() - t1))
def main():
application = webapp.WSGIApplication([('/', MainHandler)], debug=True)
util.run_wsgi_app(application)
if __name__ == '__main__':
main()
The Memcache call still pickles the object with or without using protobuf. Pickle is faster with a protobuf object since it has a very simple model
Plain pickle objects are larger than protobuf+pickle objects, hence they save time on Memcache, but there is more processor time in doing the protobuf conversion
Therefore in general either method works out about the same...but
The reason you should use protobuf is it can handle changes between versions of the models, whereas Pickle will error. This problem will bite you one day, so best to handle it sooner
Both pickle and protobufs are slow in App Engine since they're implemented in pure Python. I've found that writing my own, simple serialization code using methods like str.join tends to be faster since most of the work is done in C. But that only works for simple datatypes.
One way to do it more quickly is to turn your model into a dictionary and use the native eval / repr function as your (de)serializers -- with caution of course, as always with the evil eval, but it should be safe here given that there is no external step.
Below an example of a class Fake_entity implementing exactly that.
You first create your dictionary through fake = Fake_entity(entity) then you can simply store your data via memcache.set(key, fake.serialize()). The serialize() is a simple call to the native dictionary method of repr, with some additions if you need (e.g. add an identifier at the beginning of the string).
To fetch it back, simply use fake = Fake_entity(memcache.get(key)). The Fake_entity object is a simple dictionary whose keys are also accessible as attributes. You can access your entity properties normally, except referenceProperties give keys instead of fetching the object (which is actually quite useful). You can also get() the actual entity with fake.get(), or more interestigly, change it and then save with fake.put().
It does not work with lists (if you fetch multiple entities from a query), but could be easily be adjusted with join/split functions using an identifier like '### FAKE MODEL ENTITY ###' as the separator. Use with db.Model only, would need small adjustments for Expando.
class Fake_entity(dict):
def __init__(self, record):
# simple case: a string, we eval it to rebuild our fake entity
if isinstance(record, basestring):
import datetime # <----- put all relevant eval imports here
from google.appengine.api import datastore_types
self.update( eval(record) ) # careful with external sources, eval is evil
return None
# serious case: we build the instance from the actual entity
for prop_name, prop_ref in record.__class__.properties().items():
self[prop_name] = prop_ref.get_value_for_datastore(record) # to avoid fetching entities
self['_cls'] = record.__class__.__module__ + '.' + record.__class__.__name__
try:
self['key'] = str(record.key())
except Exception: # the key may not exist if the entity has not been stored
pass
def __getattr__(self, k):
return self[k]
def __setattr__(self, k, v):
self[k] = v
def key(self):
from google.appengine.ext import db
return db.Key(self['key'])
def get(self):
from google.appengine.ext import db
return db.get(self['key'])
def put(self):
_cls = self.pop('_cls') # gets and removes the class name form the passed arguments
# import xxxxxxx ---> put your model imports here if necessary
Cls = eval(_cls) # make sure that your models declarations are in the scope here
real_entity = Cls(**self) # creates the entity
real_entity.put() # self explanatory
self['_cls'] = _cls # puts back the class name afterwards
return real_entity
def serialize(self):
return '### FAKE MODEL ENTITY ###\n' + repr(self)
# or simply repr, but I use the initial identifier to test and eval directly when getting from memcache
I would welcome speed tests on this, I would assume this is quite faster than the other approaches. Plus, you do not have any risks if your models have changed somehow in the meantime.
Below an example of what the serialized fake entity looks like. Take a particular look at datetime (created) as well as reference properties (subdomain) :
### FAKE MODEL ENTITY ###
{'status': u'admin', 'session_expiry': None, 'first_name': u'Louis', 'last_name': u'Le Sieur', 'modified_by': None, 'password_hash': u'a9993e364706816aba3e25717000000000000000', 'language': u'fr', 'created': datetime.datetime(2010, 7, 18, 21, 50, 11, 750000), 'modified': None, 'created_by': None, 'email': u'chou#glou.bou', 'key': 'agdqZXJlZ2xlcgwLEgVMb2dpbhjmAQw', 'session_ref': None, '_cls': 'models.Login', 'groups': [], 'email___password_hash': u'chou#glou.bou+a9993e364706816aba3e25717000000000000000', 'subdomain': datastore_types.Key.from_path(u'Subdomain', 229L, _app=u'jeregle'), 'permitted': [], 'permissions': []}
Personally I also use static variables (faster than memcache) to cache my entities in the short term, and fetch the datastore when the server has changed or its memory has been flushed for some reason (which happens quite often in fact).
I want to be able to take a dynamically created string, say "Pigeon" and determine at runtime whether Google App Engine has a Model class defined in this project named "Pigeon". If "Pigeon" is the name of a existant model class, I would like to then get a reference to the Pigeon class so defined.
Also, I don't want to use eval at all, since the dynamic string "Pigeon" in this case, comes from outside.
You could try, although probably very, very bad practice:
def get_class_instance(nm) :
try :
return eval(nm+'()')
except :
return None
Also, to make that safer, you could give eval a locals hash: eval(nm+'()', {'Pigeon':pigeon})
I'm not sure if that would work, and it definitely has an issue: if there is a function called the value of nm, it would return that:
def Pigeon() :
return "Pigeon"
print(get_class_instance('Pigeon')) # >> 'Pigeon'
EDIT: Another way of doing it is possibly (untested), if you know the module:
(Sorry, I keep forgetting it's not obj.hasattr, its hasattr(obj)!)
import models as m
def get_class_instance(nm) :
if hasattr(m, nm) :
return getattr(m, nm)()
else : return None
EDIT 2: Yes, it does work! Woo!
Actually, looking through the source code and interweb, I found a undocumented method that seems to fit the bill.
from google.appengine.ext import db
key = "ModelObject" #This is a dynamically generated string
klass = db.class_for_kind(key)
This method will throw a descriptive exception if the class does not exist, so you should probably catch it if the key string comes from the outside.
There's two fairly easy ways to do this without relying on internal details:
Use the google.appengine.api.datastore API, like so:
from google.appengine.api import datastore
q = datastore.Query('EntityType')
if q.get(1):
print "EntityType exists!"
The other option is to use the db.Expando class:
def GetEntityClass(entity_type):
class Entity(db.Expando):
#classmethod
def kind(cls):
return entity_type
return Entity
cls = GetEntityClass('EntityType')
if cls.all().get():
print "EntityType exists!"
The latter has the advantage that you can use GetEntityClass to generate an Expando class for any entity type, and interact with it the same way you would a normal class.