Setting Djando field default value based on another field - django

I am creating a Django model where:
expirationTimeStamp field's default value is based on creationTimeStamp
isLive boolean field value is based on expirationTimeStamp
I have written the following functions expirationTimeCalculation and postLiveStatus and assigned them as default values to the fields but I am getting error. I have also tried to assign to respective fields through property(function) yet I am still getting error.
One of the functionality that I need to implement is that user can send custom expirationTimeStamp as well that would override default value, therefore, I believe property(function) assignment is not ideal for expirationTimeStamp field.
Is there any other way that I can go about to set the expirationTimeStamp field value based on creationTimeStamp field?
Any feedback is appreciated!
class Posts(models.Model):
def expirationTimeCalculation(self):
EXPIRATION_DURATION = 86400 #time in seconds
expirationTime = self.creationTimestamp + timedelta(seconds = EXPIRATION_DURATION)
return expirationTime
def postLiveStatus(self):
return (self.expirationTimestamp > timezone.now)
message = models.TextField()
creationTimestamp = models.DateTimeField(default=timezone.now)
expirationTimestamp = models.DateTimeField(default=expirationTimeCalculation)
isLive = models.BooleanField(default=postLiveStatus)

Similar answered question. I am attaching the official documentation as well as the link to the answered question.
Models certainly do have a "self"! It's just that you're trying to define an attribute of a model class as being dependent upon a model instance; that's not possible, as the instance does not (and cannot) exist before your define the class and its attributes.
To get the effect you want, override the save() method of the model class. Make any changes you want to the instance necessary, then call the superclass's method to do the actual saving. Here's a quick example.
def save(self, *args, **kwargs):
if not self.subject_init:
self.subject_init = self.subject_initials()
super(Subject, self).save(*args, **kwargs)
Model Overriding Documentation
Django Model Field Default Based Off Another Field

I needed field end_day to default to the last day of month in serializer. So I did this:
class MySerializer(serializers.Serializer):
year = serializers.IntegerField()
month = serializers.IntegerField()
end_day = serializers.IntegerField(required=False, default=None)
def end_day_value(self):
return self.validated_data['end_day'] or \
(datetime(year=self.validated_data['year'], month=self.validated_data['month'])+relativedelta(months=1)-relativedelta(days=1)).day
So when I need end_day or its default value I just call end_day_value method.

Related

Can I override default CharField to ChoiceField in a ModelForm?

I have a (horrible) database table that will be imported from a huge spreadsheet. The data in the fields is for human consumption and is full of "special cases" so its all stored as text. Going forwards, I'd like to impose a bit of discipline on what users are allowed to put into some of the fields. It's easy enough with custom form validators in most cases.
However, there are a couple of fields for which the human interface ought to be a ChoiceField. Can I override the default form field type (CharField)? (To clarify, the model field is not and cannot be constrained by choices, because the historical data must be stored. I only want to constrain future additions to the table through the create view).
class HorribleTable( models.Model):
...
foo = models.CharField( max_length=16, blank=True, ... )
...
class AddHorribleTableEntryForm( models.Model)
class Meta:
model = HorribleTable
fields = '__all__' # or a list if it helps
FOO_CHOICES = (('square', 'Square'), ('rect', 'Rectangular'), ('circle', 'Circular') )
...?
Perhaps you could render the forms manually, passing the options through the context and make the fields in html.
Take a look at here:https://docs.djangoproject.com/en/4.0/topics/forms/#rendering-fields-manually
I think you can easily set your custom form field as long it will match the data type with the one set in your model (e.g. do not set choices longer than max_length of CharField etc.). Do the following where foo is the same name of the field in your model:
class AddHorribleTableEntryForm(forms.ModelForm):
foo = forms.ChoiceField(choices=FOO_CHOICES)
class Meta:
model = HorribleTable
...
I think this is perfectly fine for a creation form. It's will not work for updates as the values in the DB will most probably not match your choices. For that, I suggest adding a second form handling data updates (maybe with custom permission to restrict it).
UPDATE
Another approach will be to override the forms init method. That way you can handle both actions (create and update) within the same form. Let the user select from a choice field when creating an object. And display as a normal model field for existing objects:
class AddHorribleTableEntryForm(forms.ModelForm):
foo = forms.ChoiceField(choices=FOO_CHOICES)
class Meta:
model = HorribleTable
fields = '__all__' # or a list if it helps
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
instance = kwargs.get("instance", None)
if instance is None:
self.fields["foo"].widget = forms.widgets.Select(choices=self.FOO_CHOICES)

Model Method from rest_framework modelSerializer

this is a simple question but I'm very new to django-rest-framework.
I was wondering if there is any way to access a method defined on the model from the serializer.?
Say I have a model
class Listing(models.Model):
listingid = models.BigIntegerField(primary_key=True)
mappingid = models.BigIntegerField()
projectlevelid = models.IntegerField()
subsellerid = models.IntegerField()
iscreatedbyadmin = models.BooleanField(default=None, null=True)
createdon = models.DateTimeField(auto_now_add=True, editable=False)
validationstatus = models.SmallIntegerField(default=0)
def is_project(self):
""" Returns True if listing is of Project Type (projectlevelid=6) else False"""
if self.projectlevelid == 6:
return True
else:
return False
def get_project_info(self):
"""Returns False if listing is not mapped to a project, else returns the project info"""
if self.is_project() == False:
return False
return models.Project.objects.get(projectid=self.mappingid)
Is it possible for the serializer
class ListingSerializer(serializers.ModelSerializer):
class Meta:
model = models.MasterListing
to have access to Listing.is_project i.e. for an object of the Listing model, can the serializer call its is_project method?
If so, can I set a field in the serializer such that if is_project returns true, the field is populated?
I am trying for something like this,
class ListingSerializer(serializers.ModelSerializer):
project = serializers.SomeRELATEDFieldTYPE() # this field if populated if the `is_project` is true
class Meta:
model = models.MasterListing
I understand I can do this using some combination of required=False and SerializerMethodField, but maybe there is a simpler way?.
Note: It is not possible for me to set a foreign key to the mappingid, since it depends on the projectlevelid. I also can't affect this relationship so no further normalization is possible. I know that there might be some way using content-types, but we are trying to avoid that if it is possible..
EDIT: I solved the problem, but not as the question specified.
I used this:
class ListingSerializer(serializers.ModelSerializer):
project = serializers.SerializerMethodField()
def get_project(self, obj):
"""Returns False if listing is not mapped to a project, else returns the project info"""
if str(obj.projectlevelid) == str(6):
projectObj = models.Project(projectid=obj.mappingid)
projectObjSerialized = ProjectSerializer(projectObj)
return projectObjSerialized.data
return False
class Meta:
model = models.MasterListing
So, the original question still stands: "Is it possible for the modelSerializer to access its models methods?"
Also, another problem that now appears is, can I make the serializer exclude fields on demand, i.e. can it exclude mappingid and projectlevelid if it is indeed a project?
For your first question source attribute is the answer, citing:
May be a method that only takes a self argument, such as
URLField('get_absolute_url')
For your second answer, yes it is also possible. Check the example it provides in their docs: http://www.django-rest-framework.org/api-guide/serializers/#dynamically-modifying-fields
PS: I really love drf for its very complete documentation =).
EDIT
To use the source attribute you can just declare a new explicit field like so:
is_project = serializers.BooleanField(source='is_project')
With this, is_project field has the value of the is_project method of your instance. Having this, when creating the dynamic serializer (by modifying its init method) you can add the 'project' field if it's True.
#argaen is absolutely right, source is a DRF core argument, and would most definitely solve your problem. However, it's redundant to use source, if the field name is the same as the source. So the above answer won't require you specify source, since field name is_project is the same as source name is_project.
So in your case:
is_project = serializers.BooleanField()

Update only specific fields in a models.Model

I have a model
class Survey(models.Model):
created_by = models.ForeignKey(User)
question = models.CharField(max_length=150)
active = models.NullBooleanField()
def __unicode__(self):
return self.question
and now I want to update only the active field. So I do this:
survey = get_object_or_404(Survey, created_by=request.user, pk=question_id)
survey.active = True
survey.save(["active"])
Now I get an error IntegrityError: PRIMARY KEY must be unique.
Am I right with this method to update?
To update a subset of fields, you can use update_fields:
survey.save(update_fields=["active"])
The update_fields argument was added in Django 1.5. In earlier versions, you could use the update() method instead:
Survey.objects.filter(pk=survey.pk).update(active=True)
Usually, the correct way of updating certain fields in one or more model instances is to use the update() method on the respective queryset. Then you do something like this:
affected_surveys = Survey.objects.filter(
# restrict your queryset by whatever fits you
# ...
).update(active=True)
This way, you don't need to call save() on your model anymore because it gets saved automatically. Also, the update() method returns the number of survey instances that were affected by your update.

Django custom update model form - display selected field of related model rather than foreign key id.

My question is: is there a way to create custom model form that will use a specified field from a related model rather than the related model's id?
To clarify, if I have the following two models:
class ModelOne(models.Model):
id = models.AutoField(primary_key = True)
name = models.CharField(unique = True, blank = False, null = False)
class ModelTwo(models.Model):
id = models.AutoField(primary_key = True)
parent = models.ForeignKey(ModelOne, blank = False, null = False)
attribute_1 = models.CharField(blank = False, null = False)
attribute_2 = models.IntegerField(blank = False, null = False)
Now if I create an UpdateView on ModelTwo using a ModelForm then the parent field will be pre-filled with the corresponding id from ModelOne. However I want it to display the name attribute of ModelOne and then on form submission parse the unique name (of ModelOne) to the corresponding instance of ModelOne. The reason I want to do it this way, is that I believe it is far more intuitive from a users perspective to deal with the name of ModelOne (when updating a ModelTwo instance) rather than its "id".
Any suggestions of how I can do this?
Firstly, try defining the unicode method on ModelOne. It might not apply to the solution, but it's worth having - it will drive the text values in a form Select widget...
def __unicode__(self):
'''Warning: be careful not to use related objects here,
could cause unwanted DB hits when debugging/logging
'''
return self.name
If that's not sufficient, something like this might work (it is adapted from a form I have that updates the user's name attached to a profile)...
class M2Form(forms.ModelForm):
m1_name = forms.CharField()
class Meta:
model = ModelTwo
def save(self, *args, **kw):
# Update your name field here, something like
if self.cleaned_data.get('m1_name'):
self.instance.parent = ModelOne.objects.get(name=self.cleaned_data.get('m1_name'))
return super(M2Form, self).save(*args, **kw)
This is untested, and you'll likely need to adapt this to validate that the name exists and make sure the original parent field doesn't appear on the form. With any luck, the first answer covers what I think your question is.
Using Rog's answer as a starting point and delving through some of Django's internals I eventually came to a working solution. Given my level of Django knowledge, I imagine there is a better way of doing this; so if you have another method please add it.
So based on the above two models, I created the following form class:
class CustomForm(forms.ModelForm):
parent = models.CharField(label='Name')
class Meta:
model = ModelTwo
exclude = ['parent']
def __init__(self,*args,**kwargs):
# The line of code below is the one that I was looking for. It pre-populates
# the "parent" field of the form with the "name" attribute of the related
# ModelOne instance.
kwargs['initial']['parent'] = kwargs['instance'].parent.name
super(CustomForm,self).__init__(*args,**kwargs)
# The next line is for convenience and orders the form fields in our desired
# order. I got this tip from:
# http://stackoverflow.com/questions/913589/django-forms-inheritance-and-order-of-form-fields
self.fields.keyOrder = ['parent','attribute_1','attribute_2']
def save(self, *args, **kwargs):
if self.cleaned_data.get('parent'):
# This section of code is important because we need to convert back from the
# unique 'name' attribute of ModelOne to the corresponding instance so that
# ModelTwo can be saved. Thanks goes to Rog for this section of code.
self.instance.parent = ModelOne.objects.get(name=self.cleaned_data.get('parent'))
return super(CustomForm, self).save(*args, **kwargs)

Django: models last mod date and mod count

I have a django model called Blog.
I'd like to add a field to my current model that is for last_modified_date. I know how to set a default value, but I would like somehow for it to get automatically updated anytime I modify the blog entry via the admin interface.
Is there some way to force this value to the current time on each admin site save?
Also would there be some way to add a mod_count field and have it automatically calculated on each modify of the admin site blog entry?
Create a DateTimeField in your model. Have it update whenever it is saved. This requires you to use the auto_now_add option:
class DateTimeField([auto_now=False, auto_now_add=False, **options])
DateTimeField.auto_now_add¶
Automatically set the field to now every time the object is saved. Useful
for "last-modified" timestamps. Note
that the current date is always used;
it's not just a default value that you
can override.
It should look something like this:
class Message(models.Model):
message = models.TextField()
active = models.BooleanField(default=True)
created_at = models.DateTimeField(auto_now_add=True)
Model field reference
For the second part, I think you have to overload
ModelAdmin.save_model(self, request, obj, form, change)
As James Bennett describes here. It will look something like this:
class EntryAdmin(admin.ModelAdmin):
def save_model(self, request, obj, form, change):
if change:
obj.change_count += 1
obj.save()
The accepted answer is no longer correct.
For newer django versions, you will have to use the auto_now=True parameter rather than the auto_now_add=True, which will only set the field value when the object is initially created.
From the documentation:
DateField.auto_now_add¶
Automatically set the field to now when the
object is first created. Useful for creation of timestamps.
The desired functionality is now implemented by auto_now:
DateField.auto_now¶
Automatically set the field to now every time the
object is saved.
So to achieve self-updating timestamps a model should be created like this:
class Message(models.Model):
message = models.TextField()
active = models.BooleanField(default=True)
created_at = models.DateTimeField(auto_now=True)
mod_count = models.IntegerField(default=0)
To increment mod_count everytime this model is modified overload the model's save() method:
def save(self, *args, **kwargs):
self.mod_count +=1
return super(Message,self).save(*args, **kwargs)
There's a number of ways you can increase the edit count each time it's saved.
The model itself has a save() method, and the admin model has a model_save() method.
So for example, let's say you wanted it to increment when it was edited with the admin tool....
models.py:
class MyModel(models.Model):
edit_count = models.IntegerField()
# ... rest of model code here...
admin.py:
class MyModelAdmin(admin.ModelAdmin)
def save_model(self, request, obj, form, change):
if not change:
obj.edit_count = 1
else:
obj.edit_count += 1
obj.save()
You could do similar code off of the model save() event as well.
Something else you may be interested in is django-command-extensions. It adds 2 fields which may be helpful to you:
CreationDateTimeField - DateTimeField that will automatically set it's date when the object is first saved to the database.
ModificationDateTimeField - DateTimeField that will automatically set it's date when an object is saved to the database.
You can also use a middleware solution found here: https://bitbucket.org/amenasse/django-current-user/src/7c3c90c8f5e854fedcb04479d912c1b9f6f2a5b9/current_user?at=default
settings.py
....
MIDDLEWARE_CLASSES = (
....
'current_user.middleware.CurrentUserMiddleware',
'current_user.middleware.CreateUserMiddleware',
)
....
INSTALLED_APPS = (
'current_user',
....
....
)
models.py
class ExampleModel(models.Model):
foo = models.IntegerField()
last_user = CurrentUserField(related_name="+")
created_by = CreateUserField(related_name="+")