I am defining a field in a django form in the following two ways :
class MyForm(forms.Form):
myfield = forms.ChoiceField(choices=[(u.id,u.username) for u in User.objects.filter(type="TYPE1")])
OR
class MyForm(forms.Form):
pass
def_init_(self,*args,**kwargs):
super(MyForm,self)._init_(*args,**kwargs)
self.fields['myfield'] = forms.ChoiceField(choices=[(u.id,u.username) for u in User.objects.filter(type="TYPE1")])
Is there any different between these two approaches?? I tried to find this on web but did not get any relevant answers.
First of all, there is a special field to handle such things - ModelChoiceField
In your example the difference is the moment when code is executed.
In first approach it is executed when module with form is loaded, in second - every time the form is initialized (so basically on each request to your view). So first approach has a problem - Users will be loaded on first request. If any user registers after this moment - he will not be present in the select field until you restart the server.
Also I think it is a bad practice to introduce new field in __init__ method. If you really need something like this and you can't use ModelChoiceField the better way is
class MyForm(forms.Form):
myfield = forms.ChoiceField()
def __init__(self,*args,**kwargs):
super(MyForm,self).__init__(*args,**kwargs)
self.fields['myfield'].choices = [(u.id, u.username) for u in User.objects.filter(type="TYPE1")]
Don't you get an error when you run your server using the first way?
class MyForm(forms.Form):
myfield = forms.ChoiceField(choices=[(u.id,u.username) for u in User.objects.filter(type="TYPE1")])
If you use this method That for will be executed when the file is being read. Try using the second way or a function to execute that for and set the choices.
Usually in Form.__init__ you define some dynamic fields (for example, you want to show some checkboxes, which are set/unset according to the data from some model). In all other cases first approach is better because it's more readable.
Related
Having a bit of trouble trying to bulk add a list of items to a many to many field and though having tried various things have no clue on how to approach this. I've looked at the Django documentation and cant seem to find what I'm looking for.
Here is the code for my models:
class Subject(models.Model):
noun = models.CharField(max_length=30, null=True, blank=True)
class Knowledge(models.Model):
item_text = models.TextField()
item_subjects = models.ManyToManyField(Subject, null=True, blank=True)
def add_subjects(sender, instance, *args, **kwargs):
if instance.item_info:
item_subjects = classifier.predict_subjects(instance.item_info)
if item_subjects:
....
post_save.connect(add_subjects, sender=Knowledge)
The list is being generated by the classifer.predict_subjects function.
I have tried using the m2m_changed connector and the pre_save and post_save connect. I'm not even sure the many to many field is the right option would it be better to do make a foreign key relationship.
in place of the '...' I have tried this but it doesn't create the relationship between and only saves the last one.
for sub in item_subjects:
subject = Subject(id=instance.id, noun=sub)
subject.save()
I've also tried
instance.item_subjects = item_subjects
and a load more things that I can't really remember, I don't really think I'm in the right ballpark to be honest. Any suggestions?
edit:
ok, so I have got it adding all of the list items but still haven't managed to link these items to the many to many field.
for sub in item_subjects:
subject = Subject.objects.get_or_create(noun=sub)
edit 2:
So doing pretty much exactly the same thing outside of the loop in the Django shell seems to be working and saves the entry but it doesn't inside the function.
>>> k[0].item_subjects.all()
<QuerySet []>
>>> d, b = Subject.objects.get_or_create(noun="cats")
<Subject: cats>
>>> k[0].item_subjects.add(d)
>>> k[0].item_subjects.all()
<QuerySet [<Subject: cats>]>
edit 3
So I took what Robert suggested and it works in the shell just like above just not when using it in the admin interface. The print statements in my code show the array item being updated but it just dosen't persist. I read around and this seems to be a problem to do with the admin form clearing items before saving.
def sub_related_changed(sender, instance, *args, **kwargs):
print instance.item_subjects.all()
if instance.item_info:
item_subjects = classifier.predict_subjects(instance.item_info)
if item_subjects:
for sub in item_subjects:
subject, created = Subject.objects.get_or_create(noun=sub)
instance.item_subjects.add(subject)
print instance.item_subjects.all()
post_save.connect(sub_related_changed, sender=Knowledge)
I have tried using the function as m2m_changed signal as follows:
m2m_changed.connect(model_saved, sender=Knowledge.item_subjects.through)
But this either generates a recursive loop or doesn't fire.
Once you have the subject objects (as you have in your edit), you can add them with
for sub in item_subjects:
subject, created = Subject.objects.get_or_create(noun=sub)
instance.item_subjects.add(subject)
The "item_subjects" attribute is a way of managing the related items. The through relationships are created via the "add" method.
Once you've done this, you can do things like instance.item_subjects.filter(noun='foo') or instance.item_subjects.all().delete() and so on
Documentation Reference: https://docs.djangoproject.com/en/1.11/topics/db/examples/many_to_many/
EDIT
Ahh I didn't realize that this was taking place in the Django Admin. I think you're right that that's the issue. Upon save, the admin calls two methods: The first is model_save() which calls the model's save() method (where I assume this code lives). The second method it calls is "save_related" which first clears out ManyToMany relationships and then saves them based on the submitted form data. In your case, there is no valid form data because you're creating the objeccts on save.
If you put the relevant parts of this code into the save_related() method of the admin, the changes should persist.
I can be more specific about where it should go if you'll post both your < app >/models.py and your < app >/admin.py files.
Reference from another SO question:
Issue with ManyToMany Relationships not updating inmediatly after save
I think I have a pretty common use case and am surprised at how much trouble it's giving me.
I want to use a key-value pair for a ReferenceField in the Flask-Admin edit form generated by the following two classes:
class Communique(db.Document):
users = db.ListField(db.ReferenceField(User), default=[])
class User(db.Document):
email = db.StringField(max_length=255, required=True)
def __unicode__(self):
return '%s' % self.id
I want the select to be constructed out of the ObjectId and the an email field in my model.
By mapping the __unicode__
attribute to the id field I get nice things on the mongoengine side like using the entire object in queries:
UserInformation.objects(user=current_user)
This has the unfortunate effect of causing the Flask-Admin form to display the mongo ObjectId in the edit form like so:
The docs say I have to provide the label_attr to the ModelSelectMultipleField created by Flask-Admin. I've done so by overriding the get_form method on my ModelView:
def get_form(self):
form = super(ModelView, self).get_form()
form.users = ModelSelectMultipleField(model=User,
label_attr='email',
widget=form.users.__dict__['kwargs']['widget'])
return form
I'm reusing the the widget used by the original form.users (which may be wrong). It works fine when editing an existing item, BUT throws an exception when creating a new one (perhaps because I'm reusing the widget).
All of this seems like way more work than should be needed to simply provide a label_attr to my SelectField. Fixing up the listing view was a simple matter of adding an entry to the column_formatters dictionary. Is there no simple way to specify the label_attr when creating my ModelView class?
I know I could make this problem go away by returning the email property in the __unicode__ attribute, but I feel like I shouldn't have to do that! Am I missing something?
Oy, now I see how to do it, though it's not that obvious from the docs. form_args is a dictionary with items keyed to the form models. All I needed to do was...
form_args = dict(users=dict(label_attr='email'))
Which does seem about the right amount of effort (considering Flask-Admin isn't some sort of java framework).
Here is an abstract base class for many of my "Treatment" models (TreatmentA, TreatmentB, etc):
class TreatmentBase(models.Model):
URL_PREFIX = '' # child classes define this string
code = shared.models.common.RandomCharField(length=6)
class Meta:
abstract = True
Each Treatment instance has a URL, that when visited by a user, takes them to a page specific to that treatment. I want to be able to create a Treatment in Django Admin, and immediately get this URL so I can send it to users. This URL can be created with the following method on TreatmentBase:
def get_url(self):
return '{}/{}/'.format(self.URL_PREFIX, self.code)
However, I am stuck with how to get this URL to display in Django Admin. I can think of the following solutions:
(1) Customize the display of the code field so that it becomes a clickable URL. Problem: I don't know how to do this.
(2) Add the get_url method to ModelAdmin.list_display. Problem: This means I would have to define a separate list_display for each of the child models of BaseTreatment, and I would have to explicitly list all the fields of the model, meaning I have to update it every time I modify a model, violating DRY.
(3) Add an extra field like this:
url = models.URLField(default = get_url)
Problem: get_url is an instance method (since it needs to refer to the self.code field), and from my reading of the docs about the default argument, it just has to be a simple callable without arguments.
Any way to do this seemingly simple task?
You could go with option 2 (adding to the admin display) but add it to the
readonly_fields which may alleviate your DRY concerns when models changes.
Option 3 (the extra field) could also work if you override the save method setting the URL property. You'd either want to set the field as readonly in the admin or only set the value in the save method if it's currently None.
Im working on a django application and I can't seem to get this one piece of code working. I know of some hacky ways to accomplish my task, but it seems like there should be a better way. I have a model class with one field in it:
class MobileUser(models.Model):
phone_id = models.AutoField(primary_key=True)
and everything is groovy. However, when I want to create an instance of the class and save it to the database like so:
mobile = MobileUser()
mobile.save()
I get a warning saying that MobileUser has no default value arguments, which makes sense. I know I can do things like get the last inserted row/the max id + 1 and pass that in as an argument but I'd prefer not to do that. Any ideas? Oh, and side note, the operation works it just throws a warning.
Why not let django handle it then, just do this:
class MobileUser(models.Model):
pass
Whenever you create an entry it would auto increment the id field.
I have the following in my model:
class info(models.Model):
add = models.CharField(max_length=255)
name = models.CharField(max_length=255)
An in the views when i say
info_l = info.objects.filter(id=1)
logging.debug(info_l.name)
i get an error saying name doesnt exist at debug statement.
'QuerySet' object has no attribute 'name'
1.How can this be resolved.
2.Also how to query for only one field instead of selecting all like select name from info.
1. Selecting Single Items
It looks like you're trying to get a single object. Using filter will return a QuerySet object (as is happening in your code), which behaves more like a list (and, as you've noticed, lacks the name attribute).
You have two options here. First, you can just grab the first element:
info_l = info.objects.filter(id=1)[0]
You could also use the objects.get method instead, which will return a single object (and raise an exception if it doesn't exist):
info_l = info.objects.get(id=1)
Django has some pretty good documentation on QuerySets, and it may be worth taking a look at it:
Docs on using filters
QuerySet reference
2. Retrieving Specific Fields
Django provides the defer and only methods, which will let you choose specific fields from the database, rather than fetching everything at once. These don't actually prevent the fields from being read; rather, it loads them lazily. defer is an "opt-in" mode, which lets you specify what fields should be lazily loaded. only is "out-out" -- you call it, and only the fields you pass will by eagerly loaded.
So in your example, you'd want to do something like this:
info_l = info.objects.filter(id=1).only('name')[0]
Though with a model as simple as the example you give, I wouldn't worry much at all about limiting fields.