Django: v2.1.5
DRF: v3.9.1
mariaDB: v10.3
Hi, I am a DRF newbie and I have been struggling with json field.
DRF does not support official json field type working with mariaDB and even though there is a 3rd-party package for mysql(django-mysql) but not compatible with mariaDB.
So I searched and started implementing custom jsonfield and it looks like:
model.py:
class JSONField(models.TextField):
def to_dict(self, value):
""" convert json string to python dictionary """
return json.loads(value)
def to_json(self, value):
""" convert python dictionary to json string """
return json.dumps(value)
def from_db_value(self, value, expression, connection):
""" convert string from db to python dictionary """
if value is None:
return value
return self.to_dict(value)
def to_python(self, value):
""" convert model input value to python dictionary """
if isinstance(value, dict):
return value
if value is None:
return value
return self.to_dict(value)
def get_prep_value(self, value):
""" convert python dictionary to string before writing to db """
return self.to_json(value)
class Project(models.Model):
objects = models.Manager()
project_user = JSONField(null=True)....
serializers.py:
class ProjectSerializer(serializers.ModelSerializer):
class Meta:
model = Project
fields = ('project_code'...)
def create(self, validated_data):
"""
Create and return a new `Project` instance, given the validated data.
"""
return Project.objects.create(**validated_data)
views.py:
class ListCreateProjectView(APIView):
"""
POST admin/_proj_/
: create a project
"""
def post(self, request, format=None):
serializer = ProjectSerializer(data=request.data)
if serializer.is_valid():
serializer.save()
return Response(data=serializer.data)
else:
return Response(data=serializer.errors)
please let me know what I am doing wrong here or a way to use 3rd party package rather than custom jsonfield
Thanks a lot and have a great day guys!
For people who suffer from this kind of problem, I actually solved this problem, but in an informal way. I set JSONfield as a textfield in DB, and handle (str->json),(json->str) in the view. But again, this is an informal way (I think) and you will need another solution than this. If you find one, please share it for me and other people :)
Related
I have a custom serializer that is returning a string representation of JSON. This serializer uses django.contrib.gis.serializers.geojson.Serializer which is much faster than the DRF serializer. The downside of this serializer is that it returns everything already serialized into a string, rather than as a JSON serializiable object.
Is there a way to shortcut the DRF obj>json string process and just pass the string as the json response?
Currently I am doing the following, but the obj>string>dict>string process is not ideal:
from django.contrib.gis.serializers.geojson import Serializer
from json import loads
class GeoJSONFastSerializer(Serializer):
def __init__(self, *args, **kwargs):
self.instances = args[0]
super().__init__()
#property
def data(self):
# The use of json.loads here to deserialize the string,
# only for it to be reserialized by DRF is inefficient.
return loads(self.serialize(self.instances))
Which is implemented (simplified version) in the view:
from rest_framework.mixins import ListModelMixin
from rest_framework.viewsets import GenericViewSet
class GeoJSONPlaceViewSet(ListModelMixin, GenericViewSet):
serializer_class = GeoJSONFastSerializer
queryset = Places.objects.all()
I think that you could define a custom renderer and just pass the data, something like this,
from django.utils.encoding import smart_unicode
from rest_framework import renderers
class AlreadyJSONRenderer(renderers.BaseRenderer):
media_type = 'application/json'
format = 'json'
def render(self, data, media_type=None, renderer_context=None):
return data
and in the view just add
renderer_classes = [AlreadyJSONRenderer]
Hi my client api will send me char array like=>
["user1","user2","user3",...]
My model field is CharField like=>
emplist = models.CharField(max_length=1000,null=False,blank=False)
I would like to convert this array input to string in serializer and string output to array in the serializer. Can I do that?
How can I handle this array with any other way?
You can definitely handle with a couple of tweaks on your Model.
Alter your emplist field to become _emplist
_emplist = models.CharField(max_length=1000, null=False, blank=False)
Add property methods to your model for emplist
#property
def emplist(self):
return self._emplist.split(',')
#emplist.setter
def emplist(self, value):
if isinstance(value, list):
self._emplist = ','.join(value)
elif isinstance(value, str):
self._emplist = value
Now in your Serializer just add ListSerializer field to you emplist field
emplist = serializers.ListSerializer(child=serializers.CharField(allow_blank=False, allow_null=False))
And now it is going to work perfectly for this case.
I have two models (Like and News). I am using django-rest-framework to make a web api out of it.
class Like(models.Model):
user = models.ForeignKey(User)
content_type = models.ForeignKey(ContentType)
object_id = models.PositiveIntegerField()
content_object = GenericForeignKey('content_type', 'object_id')
class News(models.Model):
user = models.ForeignKey(User)
title = models.CharField(max_length=150)
...
likes = GenericRelation(Like)
A Like object has its own user field to store who liked the News object. Now to check if a specific user exists in any of the likes of a News object, I am getting request.user from a SerializerMethodField.
class NewsSerializer(serializers.HyperlinkedModelSerializer):
user = UserSerializer()
likes_count = serializers.IntegerField(source='likes.count', read_only=True)
user_in_likes = serializers.SerializerMethodField()
class Meta:
model = News
fields = ('user', 'title', 'body', 'article_image', 'pub_date', 'likes_count', 'user_in_likes')
def get_user_in_likes(self, obj):
user = self.context['request'].user
what = obj.likes.filter(user=user).exists()
return what
When I go the /news/ url, I get the json objects including the user_in_likes to true/false for each news object.
However, I have another serialzer for different model which imports NewsSerializer class and other similar serializers:
class ActivityObjectRelatedField(serializers.RelatedField):
def to_representation(self, value):
if isinstance(value, User):
serializer = UserSerializer(value)
elif isinstance(value, Job):
serializer = JobSerializer(value)
elif isinstance(value, News):
serializer = NewsSerializer(value)
elif isinstance(value, Tender):
serializer = TenderSerializer(value)
else:
raise Exception('Unexpected type of tagged object')
return serializer.data
class ActivitySerializer(serializers.HyperlinkedModelSerializer):
actor = ActivityObjectRelatedField(read_only=True)
target = ActivityObjectRelatedField(read_only=True)
class Meta:
model = Activity
fields = ('url', 'actor', 'verb', 'target', 'pub_date')
Now if I visit /activities/, to get the activities objects I am getting an error:
KeyError at /activities/
'request'
And it points to the line of SerializerMethod of NewsSerialize class where self.context['request'].user is used.
Exception Location: /vagrant/myproject/news/serializers.py in get_user_in_likes, line 25
Again if I visit /news/ url, everything is fine and I get news objects. What am I missing here? Why is request not being recognized in the ActivitiesSerializer class? Please help me solve this problem. Thank you.
You are getting this error because you are not passing request in the context when instantiating the NewsSerializer class or other similar serializers in the to_representation() method.
You are manually instantiating the particular serializer class in to_representation() method. So, after instantiation, that particular serializer does not have access to ActivitySerializer's context thereby leading to the error.
You can pass the ActivitySerializer's context during instantiation of the relevant serializer in the to_representation() method.
class ActivityObjectRelatedField(serializers.RelatedField):
def to_representation(self, value):
if isinstance(value, User):
serializer = UserSerializer(value, context=self.context) # pass context
elif isinstance(value, Job):
serializer = JobSerializer(value, context=self.context) # pass context
elif isinstance(value, News):
serializer = NewsSerializer(value, context=self.context) # pass context
elif isinstance(value, Tender):
serializer = TenderSerializer(value, context=self.context) # pass context
else:
raise Exception('Unexpected type of tagged object')
return serializer.data
It seems like you don't populate the context dictionary of NewsSerializer with your request in the /activities/ view.
You probably use a class based view provided by Django REST Framework which populates this dictionary for you (see the get_serializer_context() method) and passes it to the Serializer instance. That's why it's automatically available to your serializer in your /news/ view.
In your /activities/ view, though, the context is passed to ActivitySerializer and isn't (automatically) propagated further from there. That's why there's no request key in your context dictionary of NewsSerializer. You would need to pass your request object to the NewsSerializer instance. To pass extra context to a Serializer you can add a context parameter containing a dictionary when instantiating (see the DRF documentation).
I have started to play around with the Django REST framework. So far I succeeded in creating a serializer for my object, creating the post view, post objects and return objects via Javascript's $.post(). So right now I have a proper conversion between my JSONs and Django model objects.
The problem is that I have an array of objects [A1, A2, ..., An]. Right now when I need to post such an array I do it object by object. Is there any possibility to post the whole array at once, and recover an array of objects inside my Django View? If so, what is the pattern to follow here? I guess I could define a new model which is an array of my current model, create a serializer for it, etc., but this does not seem too elegant.
Below are my view and serializer:
#serializers.py
class SearchRequestSerializer(serializers.ModelSerializer):
def create(self):
return SearchRequest(**self.validated_data)
class Meta:
model = SearchRequest
#views.py
#api_view(['POST'])
def post_calculation(request):
if request.method == 'POST':
#JSON to serializer object
serializer = SearchRequestSerializer(data=request.data, many=False)
if (serializer.is_valid() == False):
return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
#create the Python object
search_request = serializer.create()
#-- I do some processing stuff with the search_request object here ---
#object back to JSON
serializer3 = SearchRequestSerializer(search_request, many=False)
return Response(serializer3.data)
There are two solutions to your problem:
The first solution is to override the .create() method of your view
By default, django rest framework assumes you are passing it a single object. To account for the possibility to pass it a list of objects you might rewrite it as follows:
def create(self, request, pk=None, company_pk=None, project_pk=None):
is_many = isinstance(request.data, list)
serializer = self.get_serializer(data=request.data, many=is_many)
serializer.is_valid(raise_exception=True)
self.perform_create(serializer)
headers = self.get_success_headers(serializer.data)
return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)
Now your view will handle both single objects in POST data as well as a list of objects.
The second solution is to use a third party package
django-rest-framework-bulk provides the above functionality plus additional features (e.g. bulk update). You can check it out and decide whether it fits your needs.
Update: The solution for function based views
In order to get it to work with your function based view, the approach is similar:
#api_view(['POST'])
def post_calculation(request):
if request.method == 'POST':
is_many = isinstance(request.data, list)
# JSON to serializer object
serializer = SearchRequestSerializer(data=request.data, many=is_many)
if not serializer.is_valid():
return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
serializer.save()
#-- do some processing stuff here ---
return Response(serializer.data)
Do not call .create() method directly, use .save() instead. Also, when using many=False on serializer, the created instance is available under serializer.instance. I am not sure how to obtain the list of created instances though. You can try the same serializer.instance. If it doesn't work, try to find how to get it.
I'm learning Backbone.js and Flask (and Flask-sqlalchemy). I chose Flask because I read that it plays well with Backbone implementing RESTful interfaces. I'm currently following a course that uses (more or less) this model:
class Tasks(db.Model):
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(80), unique=True)
completed = db.Column(db.Boolean, unique=False, default=False)
def __init__(self, title, completed):
self.title = title
self.completed = completed
def json_dump(self):
return dict(title=self.title, completed=self.completed)
def __repr__(self):
return '<Task %r>' % self.title
I had to add a json_dump method in order to send JSON to the browser. Otherwise, I would get errors like object is not JSON serializable, so my first question is:
Is there a better way to do serialization in Flask? It seems that some objects are serializable but others aren't, but in general, it's not as easy as I expected.
After a while, I ended up with the following views to take care of each type of request:
#app.route('/tasks')
def tasks():
tasks = Tasks.query.all()
serialized = json.dumps([c.json_dump() for c in tasks])
return serialized
#app.route('/tasks/<id>', methods=['GET'])
def get_task(id):
tasks = Tasks.query.get(int(id))
serialized = json.dumps(tasks.json_dump())
return serialized
#app.route('/tasks/<id>', methods=['PUT'])
def put_task(id):
task = Tasks.query.get(int(id))
task.title = request.json['title']
task.completed = request.json['completed']
db.session.add(task)
db.session.commit()
serialized = json.dumps(task.json_dump())
return serialized
#app.route('/tasks/<id>', methods=['DELETE'])
def delete_task(id):
task = Tasks.query.get(int(id))
db.session.delete(task)
db.session.commit()
serialized = json.dumps(task.json_dump())
return serialized
#app.route('/tasks', methods=['POST'])
def post_task():
task = Tasks(request.json['title'], request.json['completed'])
db.session.add(task)
db.session.commit()
serialized = json.dumps(task.json_dump())
return serialized
In my opinion, it seems a bit verbose. Again, what is the proper way to implement them? I have seen some extensions that offer RESTful interfaces in Flask but those look quite complex to me.
Thanks
I would use a module to do this, honestly. We've used Flask-Restless for some APIs, you might take a look at that:
https://flask-restless.readthedocs.org/en/latest/
However, if you want build your own, you can use SQLAlchemy's introspection to output your objects as key/value pairs.
http://docs.sqlalchemy.org/en/rel_0_7/core/schema.html#metadata-reflection
Something like this, although I always have to triple-check I got the syntax right, so take this as a guide more than working code.
#app.route('/tasks')
def tasks():
tasks = Tasks.query.all()
output = []
for task in tasks:
row = {}
for field in Tasks.__table__.c:
row[str(field)] = getattr(task, field, None)
output.append(row)
return jsonify(data=output)
I found this question which might help you more. I'm familiar with SQLAlchemy 0.7 and it looks like 0.8 added some nicer introspection techniques:
SQLAlchemy introspection
Flask provides jsonify function to do this. Check out its working here.
Your json_dump method is right though code can be made concise. See this code snippet
#app.route('/tasks')
def tasks():
tasks = Tasks.query.all()
return jsonify(data=[c.json_dump() for c in tasks])