I've got a problem with my code. I need to get an instance of a model that looks like this:
class Example(models.Model):
# ...
foo = models.JSONField(default={})
and depending on the user's input (JSON key). For example:
Example.objects.filter(foo__userinput = bar)
How can I manage to don't make JSON key hardcoded?
You can try filter by dict
key = 'foo__%s' % userinput
qfilter = {key: bar}
Example.objects.filter(**qfilter)
Related
I am building a key-value store REST API that will store data in a key value pair. Suppose I want to create an endpoint where I can make a GET request to values/ to get one or more values by passing one or more keys just like this:
/values?keys=key1,key2,key3
I want to know what should I do in urls.py if I want to do this variable length query.
This is my model:
class Data(models.Model):
key = models.CharField(max_length = 100)
value = models.CharField(max_length = 1000)
def __str__(self):
return '{}:{}'.format(self.key, self.value)
You don't need do anything in your url.py. You just need get your query param (in your case it is keys) in your view.py and you can do this like below:
def your_view(request):
keys = request.query_params.get('keys')
How can I use getattr without "Class" per se ?
So I have this situation: I have 'columns' that are asking mysql for specific data in a specific order. data is printed via flask/apache so that user has ability to manipulate this data. Now, From flask, POST methdd, I'm receiving changed(?) values and I am storing them in python attributes.I need to check if values within those attributes are same as in original data. Sure, I could hardcore it but I would like have possibility of change columns dynamically.
columns = ["username", "email", "admin"]
data = ("john", "john#snow.com", "True")
username = "john"
email = "different#email.com"
admin = False
Not sure how can I approach it ?
for i in data:
if i == getattr(???, 'username'):
print("it's the same")
or something like this?:
for i in data:
if i == getattr(data, '?????'):
print("it's the same")
Everything is within flask, I cannot embed it into the Class per se. So I don't have 'self' etc.
If I could create class I would probably make something like
class Myclass:
def __init__(self):
self.columns = ["username", "email", "admin"]
self.data = ("john", "john#snow.com", "True")
self.result = []
self.username = "john"
self.email = "different#email.com"
self.admin = False
def test(self):
for i in self.data:
if i == getattr(self, self.columns[self.data.index(i)]):
self.result.append("same")
else:
self.result.append("different")
return self.result
Myclass().test()
['same', 'different', 'different']
It turned out that I was looking for simple eval(). getattr() is designed for different purposes.
so simple:
for i in data:
if i == eval(cols[data.index(i)]):
print("it's the same")
did the trick
Flask is just Python code. You can create a class and use that if that fits your use-case. Or, if you used Flask-SQLAlchemy to manage database-backed data you'd have classes and instances anyway (and get easier data updates to boot).
And classes and instances are not the only objects with attributes; modules and functions have attributes too (although you wouldn't store your data as attributes on either of those), and when you look up methods on anything, you are looking up attributes too.
Pick a storage, then either wrap that storage with an instance of a class, and use getattr(), or pick a different data structure and use the methods for that data structure to get at the different fields. A dictionary, for instance, would make it trivial to get the current value for a given name.
If you do stick to instances, then note that in your loop you'd want to zip your columns and data values together:
for name, value in zip(columns, data):
if getattr(self, name) == value:
self.result.append("same")
else:
self.result.append("different")
Note that you do not have to add "self." in front, the whole point of getattr() is do the same work the . syntax does.
You probably want to put your columns and data lists together as a dictionary:
self.data = {'username': 'john', 'email': 'john#snow.com', 'admin': 'True'}
because that's how you'd process POST data from a form anyway; that way you can iterate over the dict.items() pairs, or use just the columns list to access values:
for name, value in self.data.items():
# ...
or use dict.get() to retrieve values, allowing for missing entries:
for name in self.columns:
if getattr(self, name) == self.data.get(name):
# ...
Lets say I have
import peewee
class Foo(Model):
name = CharField()
I would like to do the following:
f = {id:1, name:"bar"}
foo = Foo.create_from_dict(f)
Is this native in Peewee? I was unable to spot anything in the source code.
I've wrote this function which works but would rather use the native function if it exists:
#clazz is a string for the name of the Model, i.e. 'Foo'
def model_from_dict(clazz, dictionary):
#convert the string into the actual model class
clazz = reduce(getattr, clazz.split("."), sys.modules[__name__])
model = clazz()
for key in dictionary.keys():
#set the attributes of the model
model.__dict__['_data'][key] = dictionary[key]
return model
I have a web page that displays all the foos and allows the user to edit them. I would like to be able to pass a JSON string to the controller, where I would convert it to a dict and then make Foos out of it, so I can update as necessary.
If you have a dict, you can simply:
class User(Model):
name = CharField()
email = CharField()
d = {'name': 'Charlie', 'email': 'foo#bar.com'}
User.create(**d)
You could use PickledKeyStore which allows you to save any value as a python dict and it works like Python's pickle library.
I have the following function,
def facebooktest(request):
fb_value = ast.literal_eval(request.body)
fb_foodies = Foodie.objects.filter(facebook_id__in = fb_value.values())
for fb_foodie in fb_foodies:
state = request.user.relationships.following().filter(username = fb_foodie.user.username).exists()
userData = {
'fbid': fb_foodie.facebook_id,
'followState': int(state),
}
Basically I am checking to see which of the user's facebook friends are on my django app. If they are, return the followState. The followState basically returns a 1 or a 0. 1 if the user is already following them on my Django app and 0 if they are not following their facebook friend on my Django app.
I would like to return back a json type dictionary to that user that looks like this:
[{fbid:222222222222, followState: 0}, {fbid:111111111111, followState: 1}, {fbid:435433434534, followState:1}]
EDIT
I have the dictionary structure but I just want to return it like the structure above.
def facebooktest(request):
fb_value = ast.literal_eval(request.body)
fb_foodies = Foodie.objects.filter(facebook_id__in = fb_value.values())
response = []
for fb_foodie in fb_foodies:
state = request.user.relationships.following().filter(username = fb_foodie.user.username).exists()
userData = {
'fbid': fb_foodie.facebook_id,
'followState': int(state),
}
response.append(userData)
return json.dumps(response)
There is a function in the django.forms.models package for that: model_to_dict
from django.forms.models import model_to_dict
model_to_dict(your_model, fields=[], exclude=[])
From the help:
model_to_dict(instance, fields=None, exclude=None)
Returns a dict containing the data in ``instance`` suitable for passing as
a Form's ``initial`` keyword argument.
``fields`` is an optional list of field names. If provided, only the named
fields will be included in the returned dict.
``exclude`` is an optional list of field names. If provided, the named
fields will be excluded from the returned dict, even if they are listed in
the ``fields`` argument.
I think you're looking for this:
return HttpResponse(simplejson.dumps(response_dict), mimetype='application/json')
where 'response_dict' would be your dictionary.
I want to create a new type of field for django models that is basically a ListOfStrings. So in your model code you would have the following:
models.py:
from django.db import models
class ListOfStringsField(???):
???
class myDjangoModelClass():
myName = models.CharField(max_length=64)
myFriends = ListOfStringsField() #
other.py:
myclass = myDjangoModelClass()
myclass.myName = "bob"
myclass.myFriends = ["me", "myself", "and I"]
myclass.save()
id = myclass.id
loadedmyclass = myDjangoModelClass.objects.filter(id__exact=id)
myFriendsList = loadedclass.myFriends
# myFriendsList is a list and should equal ["me", "myself", "and I"]
How would you go about writing this field type, with the following stipulations?
We don't want to do create a field which just crams all the strings together and separates them with a token in one field like this. It is a good solution in some cases, but we want to keep the string data normalized so tools other than django can query the data.
The field should automatically create any secondary tables needed to store the string data.
The secondary table should ideally have only one copy of each unique string. This is optional, but would be nice to have.
Looking in the Django code it looks like I would want to do something similar to what ForeignKey is doing, but the documentation is sparse.
This leads to the following questions:
Can this be done?
Has it been done (and if so where)?
Is there any documentation on Django about how to extend and override their model classes, specifically their relationship classes? I have not seen a lot of documentation on that aspect of their code, but there is this.
This is comes from this question.
There's some very good documentation on creating custom fields here.
However, I think you're overthinking this. It sounds like you actually just want a standard foreign key, but with the additional ability to retrieve all the elements as a single list. So the easiest thing would be to just use a ForeignKey, and define a get_myfield_as_list method on the model:
class Friends(model.Model):
name = models.CharField(max_length=100)
my_items = models.ForeignKey(MyModel)
class MyModel(models.Model):
...
def get_my_friends_as_list(self):
return ', '.join(self.friends_set.values_list('name', flat=True))
Now calling get_my_friends_as_list() on an instance of MyModel will return you a list of strings, as required.
What you have described sounds to me really similar to the tags.
So, why not using django tagging?
It works like a charm, you can install it independently from your application and its API is quite easy to use.
I also think you're going about this the wrong way. Trying to make a Django field create an ancillary database table is almost certainly the wrong approach. It would be very difficult to do, and would likely confuse third party developers if you are trying to make your solution generally useful.
If you're trying to store a denormalized blob of data in a single column, I'd take an approach similar to the one you linked to, serializing the Python data structure and storing it in a TextField. If you want tools other than Django to be able to operate on the data then you can serialize to JSON (or some other format that has wide language support):
from django.db import models
from django.utils import simplejson
class JSONDataField(models.TextField):
__metaclass__ = models.SubfieldBase
def to_python(self, value):
if value is None:
return None
if not isinstance(value, basestring):
return value
return simplejson.loads(value)
def get_db_prep_save(self, value):
if value is None:
return None
return simplejson.dumps(value)
If you just want a django Manager-like descriptor that lets you operate on a list of strings associated with a model then you can manually create a join table and use a descriptor to manage the relationship. It's not exactly what you need, but this code should get you started.
Thanks for all those that answered. Even if I didn't use your answer directly the examples and links got me going in the right direction.
I am not sure if this is production ready, but it appears to be working in all my tests so far.
class ListValueDescriptor(object):
def __init__(self, lvd_parent, lvd_model_name, lvd_value_type, lvd_unique, **kwargs):
"""
This descriptor object acts like a django field, but it will accept
a list of values, instead a single value.
For example:
# define our model
class Person(models.Model):
name = models.CharField(max_length=120)
friends = ListValueDescriptor("Person", "Friend", "CharField", True, max_length=120)
# Later in the code we can do this
p = Person("John")
p.save() # we have to have an id
p.friends = ["Jerry", "Jimmy", "Jamail"]
...
p = Person.objects.get(name="John")
friends = p.friends
# and now friends is a list.
lvd_parent - The name of our parent class
lvd_model_name - The name of our new model
lvd_value_type - The value type of the value in our new model
This has to be the name of one of the valid django
model field types such as 'CharField', 'FloatField',
or a valid custom field name.
lvd_unique - Set this to true if you want the values in the list to
be unique in the table they are stored in. For
example if you are storing a list of strings and
the strings are always "foo", "bar", and "baz", your
data table would only have those three strings listed in
it in the database.
kwargs - These are passed to the value field.
"""
self.related_set_name = lvd_model_name.lower() + "_set"
self.model_name = lvd_model_name
self.parent = lvd_parent
self.unique = lvd_unique
# only set this to true if they have not already set it.
# this helps speed up the searchs when unique is true.
kwargs['db_index'] = kwargs.get('db_index', True)
filter = ["lvd_parent", "lvd_model_name", "lvd_value_type", "lvd_unique"]
evalStr = """class %s (models.Model):\n""" % (self.model_name)
evalStr += """ value = models.%s(""" % (lvd_value_type)
evalStr += self._params_from_kwargs(filter, **kwargs)
evalStr += ")\n"
if self.unique:
evalStr += """ parent = models.ManyToManyField('%s')\n""" % (self.parent)
else:
evalStr += """ parent = models.ForeignKey('%s')\n""" % (self.parent)
evalStr += "\n"
evalStr += """self.innerClass = %s\n""" % (self.model_name)
print evalStr
exec (evalStr) # build the inner class
def __get__(self, instance, owner):
value_set = instance.__getattribute__(self.related_set_name)
l = []
for x in value_set.all():
l.append(x.value)
return l
def __set__(self, instance, values):
value_set = instance.__getattribute__(self.related_set_name)
for x in values:
value_set.add(self._get_or_create_value(x))
def __delete__(self, instance):
pass # I should probably try and do something here.
def _get_or_create_value(self, x):
if self.unique:
# Try and find an existing value
try:
return self.innerClass.objects.get(value=x)
except django.core.exceptions.ObjectDoesNotExist:
pass
v = self.innerClass(value=x)
v.save() # we have to save to create the id.
return v
def _params_from_kwargs(self, filter, **kwargs):
"""Given a dictionary of arguments, build a string which
represents it as a parameter list, and filter out any
keywords in filter."""
params = ""
for key in kwargs:
if key not in filter:
value = kwargs[key]
params += "%s=%s, " % (key, value.__repr__())
return params[:-2] # chop off the last ', '
class Person(models.Model):
name = models.CharField(max_length=120)
friends = ListValueDescriptor("Person", "Friend", "CharField", True, max_length=120)
Ultimately I think this would still be better if it were pushed deeper into the django code and worked more like the ManyToManyField or the ForeignKey.
I think what you want is a custom model field.