usually I use POST or GET requests except for GET.get paginations, but I don't understand the concept there are only two possibilities POST or GET .
example even if there is the same effect I do not understand the difference between
request.GET.get('page') and request.GET["page"] request.POST['rate'] and request.POST.get('rate')
request.POST is a dict-like object.
For dicts and their derivatives, d[x] equates to indexing into the dict by key x, and d.get(x, default) is a method that is equivalent to indexing, except it returns a default value instead of throwing a KeyError. If the default value is not set, d.get() will return None.
request.POST['sth'] will raise a KeyError exception if 'sth' is not in request.POST.
request.POST.get('sth') will return None if 'sth' is not in request.POST
Related
What is the difference between:
request.post.get('blog','')
AND
request.post.get('blog')
I am not able to figure out what is the difference between these two and what they return.
request.post.get('blog','') will return an empty string if the value is missing in the POST, as you defined it as default in the .get()
request.post.get('blog') will return None if the value is missing in the POST, as you did not defined any default value in .get()
Docs: https://docs.python.org/3/library/stdtypes.html#dict.get
The REQUESR.POST is like a normal dictionary in python, so when you trying to access an element in first example,
You telling python "return the value of BLOG and if it not there just return an empty string", and you can change the default value (the empty str) to whatever you want.
In the second example you didn't provide any default value so if there is no BLOG key in the request it will raise an ERROR, and won't return anything.
This is from print(request.POST)
<QueryDict: {'csrfmiddlewaretoken': ['2Tg4HgJ07qksb3hPUDWSQYueYOjYOkQcmzll9fnjbJ0GZHkWHdM8DtYqZB4uv3Fv'], 'username': ['boycececil'], 'password': ['password']}>
This is from print(request.POST.get('username'))
boycececil
So as you can see, list (from one of the values of QueryDict)-> string(from the get function), that's magic! Isn't it?
So, somebody know what's going on?
What the value type of the value of request.POST in django?
The type is django.http.request.QueryDict
So as you can see, list -> string, that's magic! Isn't it?
No, it isn't magic. This is just the documented behavior of QueryDict:
"QueryDict.__getitem__(key)
Returns the value for the given key. If the key has more than one value, it returns the last value. ..."
Note: if you want all values for a key, you can call getlist(key) on the QueryDict.
So, the request.POST is a subclass of the dictionary but not a raw dictionary.
It is a subclass of the django MultiValueDict class which is a subclass of dict.
When I call get(key) to the Querydict it return the last value of the list. Sounds like the get method in Querydict overwrite the get method in the raw dictionary.
Yes ... that is what the __getitem__ method does.
By the way, I wonder why we need multiple value for one key.
It is because HTTP allows multiple values for a given parameter in a request. So if multiple values can be provided, django need to be able to make them available via the HttpRequest.POST object.
But since this is an unusual case, they decided to just give your code one value for each parameter ... unless it specifically asks for them all. Django is being helpful.
When I want to select objects with a get() function like
personalProfile = World.objects.get(ID=personID)
If get function doesn't return find a value, a "matching query does not exist." error occurs.
If I don't need this error, I'll use try and except function
try:
personalProfile = World.objects.get(ID=personID)
except:
pass
But I think this is not the best way since I use
except:
pass
Please recommend some idea or code sample to fight with this issue
That depends on what you want to do if it doesn't exist..
Theres get_object_or_404:
Calls get() on a given model manager, but it raises Http404 instead of the model’s DoesNotExist exception.
get_object_or_404(World, ID=personID)
Which is very close to the try except code you currently do.
Otherwise theres get_or_create:
personalProfile, created = World.objects.get_or_create(ID=personID)
Although, If you choose to continue with your current approach, at least make sure the except is localised to the correct error and then do something with that as necessary
try:
personalProfile = World.objects.get(ID=personID)
except MyModel.DoesNotExist:
raise Http404("No MyModel matches the given query.")
The above try/except handle is similar to what is found in the docs for get_object_or_404...
A get_or_none() function has been proposed, multiple times now. The rejection notice is feature creep, which you might or might not agree with. The functionality is present --with slightly different semantics-- in the first() queryset method.
But first things first:
The manager throws World.DoesNotExist, a specialized subclass of ObjectDoesNotExist when a World object was not found:
try:
personalProfile = World.objects.get(ID=personID)
except World.DoesNotExist:
pass
There's also get_object_or_404() which raises a Http404 exception when the object was not found.
You can also roll your own get_or_none(). A possible implementation could be:
def get_or_none(queryset, *args, **kwargs):
try:
return queryset.get(*args, **kwargs)
except ObjectDoesNotExist:
return None
Note that this still raises MultipleObjectsReturned when more than one matching object is found. If you always want the first object regardless of any others, you can simplify using first(), which returns None when the queryset is empty:
def get_or_none(queryset, *args, **kwargs):
return queryset.filter(*args, **kwargs).first()
Note however, for this to work reliably, you need a proper order for objects, because in the presence of multiple objects first() might be non-deterministic (it probably returns the first object from the database index used to filter the query and neither indexes not the underlying tables need be sorted or even have a repeatable order).
Use both, however, only when the use of the object to retrieve is strictly optional for the further program flow. When failure to retrieve an object is an error, use get_object_or_404(). When an object should be created when it does not exist, use get_or_create(). In those cases, both are better suited to simplify program flow.
As alasdair mentioned you could use the built in first() method.
It returns the object if it exists or None if it's not
personalProfile = World.objects.filter(ID=personID).first()
How can I check whether an obj is in a queryset or not?
I tried this:
self.assertIn(obj, list(MyModel.objects.filter(...))
But it does not work in my case.
AssertionError: <MyModel 137 'unclassified'> not found in
[<MyModel 1676 'foo'>, ..., <MyModel 137 'unclassified'>, ...]
I don't understand it, since it is in the list.
How about
self.assertTrue(MyModel.filter(...).filter(pk=obj.pk).exists())
First of all, it should be MyModel.objects.filter(...). If you omit the .objects, you should've gotten a different error, so I'm assuming you did include it but just forgot it in the question.
If obj is actually in the QuerySet returned, what you did should have worked as Django model instances provides an equal comparator which compares both the type and the primary key. list() is not required around the QuerySet, though it should still work if you used it.
From the Django 1.5 source:
def __eq__(self, other):
return isinstance(other, self.__class__) and self._get_pk_val() == other._get_pk_val()
If it still doesn't work, there are a few possible causes:
The type doesn't match. In this case, it doesn't matter even if the object pk exists in the QuerySet's object pks. (You cannot compare apples to oranges)
There is no such object in the database (i.e. it hasn't been saved yet)
The type matches but the object is not in the QuerySet (i.e. filtered out)
You overrode the __eq__ method and did something weird. Or you overrode the default manager .objects with some custom filter. This scenario is outside the scope of this answer and if you did this, you should probably know how to fix it.
To help you diagnose which is the case, try this:
self.assertTrue(isinstance(obj, MyModel))
# 1. If it fails here, your object is an incorrect type
# Warning: the following tests can be very slow if you have a lot of data
self.assertIn(obj.pk, MyModel.objects.values_list('pk', flat=True))
# 2. If it fails here, the object doesn't exist in the database
self.assertIn(obj.pk, MyModel.objects.filter(...).values_list('pk', flat=True))
# 3. If it fails here, the object did not pass your filter conditions.
self.assertIn(obj, MyModel.objects.filter(...))
# 4. If it fails here, you probably messed with the Django ORM internals. Tsk tsk.
Just with, note the .all()
queryset_result = MyModel.filter(...).all()
if obj in queryset_result:
//obj is in the queryset
The "in" fails because the objects aren't actually equal, as equality is object identity by default. If you want "in" to work, you'd have to implement __eq__ accordingly on your model.
If you don't want to do that, you can check by comparing the pk, like so
self.assertIn(obj.pk, [o.pk for o in MyModel.filter(...)])
I think This is very simple way get to find out object present in queryset or not.
First Example:
obj_list = MyModel.filter(...)
if obj in obj_list:
print "obj in queryset"
else:
print "not in queryset"
Second Example:
obj_list = MyModel.filter(...)
try:
obj_list.get(pk=obj.id)
except:
# If try get success obj is present in query set else your this except get executed.
Suppose i have this code
if form.is_valid():
form.save()
Now suppose my form is valid i have exception that foregin key value is linked to more than one column so it will raise exception
Now i want to know is there any way to grab that exception value and pass to jquery via AJAX
Because form is valid so it comes inside the loop but its not able to go after form.save
So how can i program that if exception occurs it get passed to jquery like
if exception
return HttpResponse(exception)
I get this exception
MultipleObjectsReturned at
/manage/Source/create/ get() returned
more than one Account -- it returned
3! Lookup parameters were
{'account_number':
u'121121'}
What type of exception it is
MultipleObjectsReturned is the exception.
try:
#do something
except MultipleObjectsReturned:
return HttpResponse('MultipleObjectsReturned')
I wouldn't recommend using a bare try/except to catch all exceptions, as you won't know exactly what's wrong.