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Query by computed property in python mongoengine

I wondered if it is possible to query documents in MongoDB by computed properties using mongoengine in python.
Currently, my model looks like this:
class SnapshotIndicatorKeyValue(db.Document):
meta = {"collection": "snapshot_indicator_key_values"}
snapshot_id = db.ObjectIdField(nullable=False)
indicator_key_id = db.ObjectIdField(nullable=False)
value = db.FloatField(nullable=False)
created_at = db.DateTimeField()
updated_at = db.DateTimeField()
#property
def snapshot(self):
return Snapshot.objects(id=self.snapshot_id).first()
def indicator_key(self):
return IndicatorKey.objects(id=self.indicator_key_id).first()
When I do for example SnapshotIndicatorKeyValue .objects().first().snapshot, I can access the snapshotproperty.
But when I try to query it, it doesn't work. For example:
SnapshotIndicatorKeyValue.objects(snapshot__date_time__lte=current_date_time)
I get the error `mongoengine.errors.InvalidQueryError: Cannot resolve field "snapshot"``
Is there any way to get this working with queries?
I need to query SnapshotIndicatorKeyValue based on a property of snapshot.

In order to query the snapshot property directly through mongoengine, you can reference the related snapshot object rather than the snapshot_id in your SnapshotIndicatorKeyValue document definition.
An amended model using a Reference field would be like this:
from mongoengine import Document, ReferenceField
class Snapshot(Document)
property_abc = RelevantPropertyHere() # anything you need
class SnapshotIndicatorKeyValue(Document):
snapshot = ReferenceField(Snapshot)
You would sucessively save an instance of Snapshot and an instance of SnapshotIndicatorKeyValue like this:
sample_snapshot = Snapshot(property_abc=relevant_value_here) # anything you need
sample_snapshot.save()
sample_indicatorkeyvalue = SnapshotIndicatorKeyValue()
sample_indicatorkeyvalue.snapshot = sample_snapshot
sample_indicatorkeyvalue.save()
You can then refer to any of the snapshot's properties through:
SnapshotIndicatorKeyValue.objects.first().snapshot.property_abc

Django, transform from a queryset to json and use a value from a key

This is my model.py
class Ont_Pruebas_Json(models.Model):
usuario_id = models.CharField(max_length=12)
data = jsonfield.JSONField()
def __str__(self):
return '{}'.format(self.usuario_id)
On data field I am storing this:
{u'1': {u'user': u'user1',u'mac': u"'00:00:00:00:00:01'"}, u'2': {u'user': u'user1',u'mac': u"'00:00:00:00:00:01'"}}
On my views.py
I am passing the query set this way:
context['context_json'] = Ont_Pruebas_Json.objects.all()
How can pass from the queryset to json format so I can choose for example from 1 the key mac and get the value: 00:00:00:00:00:01.

In general, you shouldn't store json data directly in the database. There are lots of potential problems doing this. For example, if data is missing you might not know because you didn't validate it.
You should first parse your data so that python can read it. If you are using Django Rest Framework(DRF) use a serializer.
However, I found serializers confusing at the start so if you want to parse a queryset do so do as shown below.
from .models import Ont_Pruebas_Json
import json
query = Ont_Pruebas_Json.objects.get(usuario_id ='some_user_id')
data = json.loads(str(query))

Update multiple fields on Google NDB entity

Working with Google App Engine for Python, I am trying to create and then update an ndb entity. To update a single property, you can just access the property using a dot, e.g.
post.body = body
But I would like to know if there is a simple way to update multiple fields within an ndb entity. The following code:
class Create(Handler):
def post(self):
## code to get params
post = Post(author = author,
title = title,
body = body)
post.put()
class Update(Handler):
def post(self, post_id):
post = post.get_by_id(int(post_id))
fields = ['author', 'title', 'body']
data = get_params(self.request, fields)
for field in fields:
post[field] = data[field]
post.put()
The "Create" handler works fine, but the "Update" handler results in:
TypeError: 'Post' object does not support item assignment
So it seems I would need to access the properties using a dot, but that is not going to work when I have a list of properties I want to access.
Can someone provide an alternative way to update multiple properties of an NDB entity after it has been created?

You should use setattr.
for field in fields:
setattr(post, field, data[field])
(Note that GAE objects do actually provide a hidden way of updating them via a dict, but you should use the public interface.)

You can use the populate method:
post.populate(**data)

POST List of Objects w/ endpoints-proto-datastore

tl;dr: is it possible, with endpoints-proto-datastore, to receive a list with objects from a POST and insert it in the db?
Following the samples, when building my API i didn't got how could i let the users POST a list of objects so that i could be more efficient about putting a bunch of data in the db using ndb.put_multi, for example.
From this comment here at endpoints_proto_datastore.ndb.model i imagine that it is not possible with how it is designed. Am i right or i am missing something?
Extending the sample provided by endpoints achieved the desired with:
class Greeting(messages.Message):
message = messages.StringField(1)
class GreetingCollection(messages.Message):
items = messages.MessageField(Greeting, 1, repeated=True)
# then inside the endpoints.api class
#endpoints.method(GreetingCollection, GreetingCollection,
path='hellogretting', http_method='POST',
name='greetings.postGreeting')
def greetings_post(self, request):
result = [item for item in request.items]
return GreetingCollection(items=result)
-- edit --

See the docs about POSTing into the datastore, your only issue is that your models aren't EndpointsModels. Instead define a datastore model for both your Greeting and GreetingCollection:
from endpoints_proto_datastore.ndb import EndpointsModel
class Greeting(EndpointsModel):
message = ndb.StringProperty()
class GreetingCollection(EndpointsModel):
items = ndb.StructuredProperty(Greeting, repeated=True)
Once you've done this, you can use
class MyApi(remote.Service):
# ...
#GreetingCollection.method(path='hellogretting', http_method='POST',
name='greetings.postGreeting')
def greetings_post(self, my_collection):
ndb.put_multi(my_collection.items)
return my_collection

Returning extended fields in JSON

I have two tabels(Ingredient_Step and Ingredient) in on relation as you can see below:
Models.Py
class Ingredient_Step(models.Model):
ingredient = models.ForeignKey(Ingredient)
Step = models.ForeignKey(Step)
def __unicode__(self):
return u'{}'.format(self.Step)
class Ingredient(models.Model):
IngredientName = models.CharField(max_length=200,unique=True)
Picture = models.ImageField(upload_to='Ingredient')
def __unicode__(self):
return u'{}'.format(self.IngredientName)
In a function, i need serialize a JSON object from a query that returns from "Ingredient_step", but I need send the field "IngredientName", who comes from "Ingredient" table.
I try using "ingredient__IngredientName" but it fails.
Views.Py:
def IngredientByStep(request):
if request.is_ajax() and request.GET and 'id_Step' in request.GET:
if request.GET["id_Step"] != '':
IngStp = Ingredient_Step.objects.filter(Step =request.GET["id_Step"])
return JSONResponse(serializers.serialize('json', IngStp, fields=('pk','ingredient__IngredientName')))
How i can call extends field from a relation?
Thanks

This "feature" of Django (and many ORM's like SQLAlchemy) are called Lazy Loading, meaning data is only loaded from related models if you specifically ask for them. In this case, build your IngStp as a list of results, and make sure to access the property for each result before serializing.
Here's an example of how to do that: Django: Include related models in JSON string?