This seems like it should be dead simple, so I must be missing something. I just want to set the value of a field in my model instance by name. Say I have:
class Foo(Model):
bar = CharField()
f = Foo()
I want to set the value of bar by name, not by accessing the field. So something like:
f.fields['bar'] = 'BAR"
instead of
f.bar = 'BAR'
I've tried setattr but it doesn't persist the value in the database. I also tried going through _meta.fields but got various errors along the way.
If you modify the value via setattr, you need to remember to save the model after modifying it. I've been bitten in the past where I changed the values but forgot to save the model, and got the same result.
setattr(f, 'bar', 'BAR')
f.save()
We may have to see more code.
setattr(f, 'bar', 'BAR')
should work as this is how Django does it internally.
Make sure you are calling 'save', as well.
Related
I'm trying to get a unique value for a field (unique within the db column).
my code (other model fields omitted):
class PlatformUserChildren(models.Model):
dashboard = models.CharField('dashboard URL', max_length=64, unique=True, default=createDashboardCode(self))
def createDashboardCode(self):
stringCheck = False
while stringCheck is False:
newString = str(uuid.uuid4())[:32]
doesStringExist = newString in self.dashboard
if not doesStringExist:
stringCheck = True
return newString
I'm getting name 'self' is not defined as an error.
What should I be passing to the function so that I can check the db column to ensure the value is unique -or- is there a built-in way of doing this?
What I've already tried or looked at:
setting unique=True for the field and using default=uuid.uuid4 - that gives me duplicate values and generates a validation error (SO link)
I'm aware of Django 1.8's UUID field, however i'm on 1.7
The problem lies in the following line (indented for better readability) as you already know and mentioned before:
dashboard = models.CharField(
'dashboard URL',
max_length=64,
unique=True,
default=createDashboardCode(self)
)
In this part:
default=createDashboardCode(self)
you're calling the method createDashboardCode with the argument self. This is wrong, because you never pass self to a method as it is passed by Python. Whenever you call the method createDashboardCode you should do it this way:
createDashboardCode()
That's it, you're not passing the argument self explicitly.
You're getting an error "name 'self' is not defined" because self is not defined. There is no variable self in your code that you can pass to the method.
Now we're one step further, but your problem won't be solved if you just apply this slight change to your code.
The return value from the method createDashboardCode will be assigned to default. That's not what you really want. You have to assign a reference of the method to default:
default = createDashboardCode
Pay attention to the missing brackets. This will call the method every time a new instance of the model is created
Define a function:
def my_function():
print "hello"
and run it in the Python interpreter:
# once like this
my_function()
# and again like this
my_function
and you'll see the difference. That should help you to better comprehend this issue.
Is there a way to call cleaned_data on all fields with some function instead of individually calling it for each field?
Also, why do we even need to call cleaned_data?
I am not sure if I need it here... I am using a for loop to save a formset, but it only saves the last one. Here is the code
for instance in form:
tmp = instance.save(commit=False)
# it throws an error when I try to do tmp[foreign_key] = other_model
setattr(tmp, foreign_key, other_model)
tmp.save()
What are you hoping for? You don't ever call it. cleaned_data gets populated upon validating the form.
form.is_valid() populates form.cleaned_data, which is a dictionary storing all data "cleaned" i.e. validated and converted to their python types.
I don't think one can make data much more accessible than a dictionary of keys mapped to field names.
As for your latest update, that itself is pretty confusing.
You appear to be setting an attribute on a foreign key in your modelform instance based on a local variable named 'gen_house_form_saved' (which I don't understand as well: if it's in the locals() namespace, and you're not using a dynamic name, why use locals at all).
My Post model have list of authors id
class Post(Document):
authors_id = ListField(IntField(required=True), required=True)
But sometime I need to use default Django User class. How most rapidly I can do it?
(I'm using sqlite for users and sessions and MongoDB (mongoengine ODM) for other. Don't ask why:))
I was tried to write it:
def get_authors(self):
authors = list()
for i in self.authors_id:
authors.append(get_user(IntField.to_python(self.authors_id[i])))
return authors
...and it raises 'list index out of range' exception. (authors id not empty, really). What I'm doing wrong?
Not sure about the to_python method but since you are looping through the authors_id, there is no need to do
authors.append(get_user(IntField.to_python(self.authors_id[i])))
You should be good with
authors.append(get_user(IntField.to_python(i)))
Instead of
IntField.to_python(self.authors_id[i]))
I think you just need to do:
IntField.to_python(i)
In Python the 'for i in some_list' construction gives you elements of the list, not integer indexes.
You said that you were getting this error:
and unbound method to_python() must be called with IntField instance as first argument (got int instance instead)
I got a similar error from MongoEngine. In my case the problem was that I defined the field like this:
foo_id = IntField
The correct way to define it is:
foo_id = IntField()
When I added the parenthesis, the problem went away.
I have a database of exhibition listings related by foreign key to a database of venues where they take place. Django templates access the venue information in the query results through listing.venue.name, listing.venue.url, and so on.
However, some exhibitions take place in temporary venues, and that information is stored in the same database, in what would be listing.temp_venue_url and such. Because it seems wasteful and sad to put conditionals all over the templates, I want to move the info for temporary venues to where the templates are expecting info for regular venues. This didn't work:
def transfer_temp_values(listings):
for listing in listings:
if listing.temp_venue:
listing.venue = Venue
listing.venue.name = listing.temp_venue
listing.venue.url = listing.temp_venue_url
listing.venue.state = listing.temp_venue_state
listing.venue.location = listing.temp_venue_location
The error surprised me:
ValueError at /[...]/
Cannot assign "<class 'myproject.gsa.models.Venue'>": "Exhibition.venue" must be a "Venue" instance.
I rather thought it was. How do I go about accomplishing this?
The error message is because you have assigned the class Venue to the listing, rather than an instance of it. You need to call the class to get an instance:
listing.venue = Venue()
I have a Django model with some fields that have default values specified. I am looking to grab the default value for one of these fields for us later on in my code. Is there an easy way to grab a particular field's default value from a model?
TheModel._meta.get_field('the_field').get_default()
As of Django 1.9.x you may use:
field = TheModel._meta.get_field('field_name')
default_value = field.get_default()
You can get the field like this:
myfield = MyModel._meta.get_field_by_name('field_name')
and the default is just an attribute of the field:
myfield.default
if you don't want to write the field name explicitly, you can also do this:
MyModel._meta.get_field(MyModel.field.field_name).default
If you need the default values for more than one field (e.g. in some kind of reinitialization step) it may be worth to just instantiate a new temporary object of your model and use the field values from that object.
temp_obj = MyModel()
obj.field_1 = temp_obj.field_1 if cond_1 else 'foo'
...
obj.field_n = temp_obj.field_n if cond_n else 'bar'
Of course this is only worth it, if the temporary object can be constructed without further performance / dependency issues.