Say I have a User model in django and I want to add some achievements to users. So I've created an Achieve model:
class Achive:
type = ....
value = ....
status = BooleanField(default=False)
I want all those achieves be a static set of models for every user (20 instances, for example) with ability to delete old and create new achieves. The problem is how to do it. Expected flow is:
1) user granted to use achievement system;
2) user got all those achieves (in admin panel shows like a table);
3) in admin panel per user I can change status of every achieve (affects only on edited user);
4) if new Achieve instance is created — add to all users who have achievements;
5) if existed Achieve instance has been deleted — remove from all users;
Solutions with I came up:
1) use Achieve model with jsonfield. store achieves in json like dictionary, use custom widget for admin panel to show checkboxes to change status). But where to store global set of achievements to create new/delete old ones? how to manage it?
2) use many to many field to Achieve and Achieve model without status. Why: if relation between User ← → Achieve exists, that means that user earn an achieve.
Both solutions I don't really like so hope for your advice.
P.S. sqlite is used as db and not allowed to use another (like mongo, etc.)
Thanks in advance!
What you want is a ManyToMany relationship between Achieve and User, but with the ability to store extra data on the relationship (the status for example).
With a normal ManyToManyField on a Model, Django actually creates an intermediate model to store the relationships in the database. By adding a through argument to your ManyToManyField, you can specify the intermediate model used for the relationship and store extra data with the relationship, as documented here:
class Goal(models.Model):
type = ...
value = ...
achievers = models.ManyToManyField(to=User, through='Achievement', related_name='goals')
class Achievement(models.Model):
status = models.BooleanField()
date_reached = models.DateField(null=True)
goal = models.ForeignKey(to=Goal, on_delete=models.CASCADE)
achiever = models.ForeignKey(to=User, on_delete=models.CASCADE)
then you can create and query the relationships like this, assuming you have a user and a goal:
achievement = Achievement.objects.create(status=True, date_reached=date(2018, 10, 12), achiever=user, goal=goal)
user.goals.filter(achievement__status=True) # gives the achieved goals of a user
goal.achievers.filter(achievement__status=True) # gives the users that achieved a goal
I have a model named Exam. each Exam has a set of users called participants. The only way I found to keep such set in Django is to add a field in User model. But I'd prefer to write this model to be as independent as possible so if later I want to use it again I can do it without changing my User model. So How can I handle having such set without manually modifying the User model fields?
Regarding your comment here is what you could do something like this:
class Exam(models.Model):
participants = models.ManyToMany(settings.AUTH_USER_MODEL, through='Participation')
class Participation(models.Model)
user = models.OneToOneField(settings.AUTH_USER_MODEL)
exam = models.ForeignKey('Exam')
active = models.BooleanField(default=False)
Another option would be to use Django's limit_coices_to. It's not transaction-save, but might do the job. You would just limit to choices to all non-related objects.
I would like to have a model in Django that has multiple pictures associated with it. I'm evaluating possible options.
One picture for one model is easily done with the models.ImageField(...).
However, I would like a array (or set) of pictures. It can be just paths, not necessarily ImageField objects.
The problem is, how do I create that field in a Django model? I am assuming I will need to create a field that is not part of models.WhateverField. Is that possible? Can I define a non-model field, such as:
class MyModel:
name = models.CharField(max_length=10)
picture_list = []
and then do:
def sample_add_picture_view(request):
picture = "sample.jpg"
model = MyModel.objects.get(id=sample_id)
model.picture_list.append(picture)
model.save()
return HttpResponseRedirect('index.html')
Could this be done? If not, what could be a better solution? Thank you !
You need to create two separate models and link them with a ForeignKey field, like so:
class Item(models.Model):
name = models.CharField(max_length=255)
class ItemImage(models.Model):
image = models.ImageField(upload_to="item_images")
item = models.ForeignKey('Item', related_name="images")
It is possible to make a custom field to store multiple items, but it's a really bad idea. You would have to serialise an array into the database, making maintenance very difficult. Using a separate model means you can store extra information such as upload times, image captions etc with little extra effort.
So I've got a UserProfile in Django that has certain fields that are required by the entire project - birthday, residence, etc. - and it also contains a lot of information that doesn't actually have any importance as far as logic goes - hometown, about me, etc. I'm trying to make my project a bit more flexible and applicable to more situations than my own, and I'd like to make it so that administrators of a project instance can add any fields they like to a UserProfile without having to directly modify the model. That is, I'd like an administrator of a new instance to be able to create new attributes of a user on the fly based on their specific needs. Due to the nature of the ORM, is this possible?
Well a simple solution is to create a new model called UserAttribute that has a key and a value, and link it to the UserProfile. Then you can use it as an inline in the django-admin. This would allow you to add as many new attributes to a UserProfile as you like, all through the admin:
models.py
class UserAttribute(models.Model):
key = models.CharField(max_length=100, help_text="i.e. Age, Name etc")
value = models.TextField(max_length=1000)
profile = models.ForeignKey(UserProfile)
admin.py
class UserAttributeInline(admin.StackedInline):
model = UserAttribute
class UserProfile(admin.ModelAdmin):
inlines = [UserAttibuteInline,]
This would allow an administrator to add a long list of attributes. The limitations are that you cant's do any validation on the input(outside of making sure that it's valid text), you are also limited to attributes that can be described in plain english (i.e. you won't be able to perform much login on them) and you won't really be able to compare attributes between UserProfiles (without a lot of Database hits anyway)
You can store additional data in serialized state. This can save you some DB hits and simplify your database structure a bit. May be the best option if you plan to use the data just for display purposes.
Example implementation (not tested)::
import yaml
from django.db import models
class UserProfile(models.Model):
user = models.OneToOneField('auth.User', related_name='profile')
_additional_info = models.TextField(default="", blank=True)
#property
def additional_info(self):
return yaml.load(self._additional_info)
#additional_info.setter
def additional_info(self, user_info_dict):
self._additional_info = yaml.dump(user_info_dict)
When you assign to profile.additional_info, say, a dictionary, it gets serialized and stored in _additional_info instead (don't forget to save the instance later). And then, when you access additional_info, you get that python dictionary.
I guess, you can also write a custom field to deal with this.
UPDATE (based on your comment):
So it appears that the actual problem here is how to automatically create and validate forms for user profiles. (It remains regardless on whether you go with serialized options or complex data structure.)
And since you can create dynamic forms without much trouble[1], then the main question is how to validate them.
Thinking about it... Administrator will have to specify validators (or field type) for each custom field anyway, right? So you'll need some kind of a configuration option—say,
CUSTOM_PROFILE_FIELDS = (
{
'name': 'user_ip',
'validators': ['django.core.validators.validate_ipv4_address'],
},
)
And then, when you're initializing the form, you define fields with their validators according to this setting.
[1] See also this post by Jacob Kaplan-Moss on dynamic form generation. It doesn't deal with validation, though.
This is a problem concerning django.
I have a model say "Automobiles". This will have some basic fields like "Color","Vehicle Owner Name", "Vehicle Cost".
I want to provide a form where the user can add extra fields depending on the automobile that he is adding. For example, if the user is adding a "Car", he will extra fields in the form, dynamically at run time, like "Car Milage", "Cal Manufacturer".
Suppose if the user wants to add a "Truck", he will add "Load that can be carried", "Permit" etc.
How do I achieve this in django?
There are two questions here:
How to provide a form where the user can add new fields at run time?
How to add the fields to the database so that it can be retrieved/queried later?
There are a few approaches:
key/value model (easy, well supported)
JSON data in a TextField (easy, flexible, can't search/index easily)
Dynamic model definition (not so easy, many hidden problems)
It sounds like you want the last one, but I'm not sure it's the best for you. Django is very easy to change/update, if system admins want extra fields, just add them for them and use south to migrate. I don't like generic key/value database schemas, the whole point of a powerful framework like Django is that you can easily write and rewrite custom schemas without resorting to generic approaches.
If you must allow site users/administrators to directly define their data, I'm sure others will show you how to do the first two approaches above. The third approach is what you were asking for, and a bit more crazy, I'll show you how to do. I don't recommend using it in almost all cases, but sometimes it's appropriate.
Dynamic models
Once you know what to do, this is relatively straightforward. You'll need:
1 or 2 models to store the names and types of the fields
(optional) An abstract model to define common functionality for your (subclassed) dynamic models
A function to build (or rebuild) the dynamic model when needed
Code to build or update the database tables when fields are added/removed/renamed
1. Storing the model definition
This is up to you. I imagine you'll have a model CustomCarModel and CustomField to let the user/admin define and store the names and types of the fields you want. You don't have to mirror Django fields directly, you can make your own types that the user may understand better.
Use a forms.ModelForm with inline formsets to let the user build their custom class.
2. Abstract model
Again, this is straightforward, just create a base model with the common fields/methods for all your dynamic models. Make this model abstract.
3. Build a dynamic model
Define a function that takes the required information (maybe an instance of your class from #1) and produces a model class. This is a basic example:
from django.db.models.loading import cache
from django.db import models
def get_custom_car_model(car_model_definition):
""" Create a custom (dynamic) model class based on the given definition.
"""
# What's the name of your app?
_app_label = 'myapp'
# you need to come up with a unique table name
_db_table = 'dynamic_car_%d' % car_model_definition.pk
# you need to come up with a unique model name (used in model caching)
_model_name = "DynamicCar%d" % car_model_definition.pk
# Remove any exist model definition from Django's cache
try:
del cache.app_models[_app_label][_model_name.lower()]
except KeyError:
pass
# We'll build the class attributes here
attrs = {}
# Store a link to the definition for convenience
attrs['car_model_definition'] = car_model_definition
# Create the relevant meta information
class Meta:
app_label = _app_label
db_table = _db_table
managed = False
verbose_name = 'Dynamic Car %s' % car_model_definition
verbose_name_plural = 'Dynamic Cars for %s' % car_model_definition
ordering = ('my_field',)
attrs['__module__'] = 'path.to.your.apps.module'
attrs['Meta'] = Meta
# All of that was just getting the class ready, here is the magic
# Build your model by adding django database Field subclasses to the attrs dict
# What this looks like depends on how you store the users's definitions
# For now, I'll just make them all CharFields
for field in car_model_definition.fields.all():
attrs[field.name] = models.CharField(max_length=50, db_index=True)
# Create the new model class
model_class = type(_model_name, (CustomCarModelBase,), attrs)
return model_class
4. Code to update the database tables
The code above will generate a dynamic model for you, but won't create the database tables. I recommend using South for table manipulation. Here are a couple of functions, which you can connect to pre/post-save signals:
import logging
from south.db import db
from django.db import connection
def create_db_table(model_class):
""" Takes a Django model class and create a database table, if necessary.
"""
table_name = model_class._meta.db_table
if (connection.introspection.table_name_converter(table_name)
not in connection.introspection.table_names()):
fields = [(f.name, f) for f in model_class._meta.fields]
db.create_table(table_name, fields)
logging.debug("Creating table '%s'" % table_name)
def add_necessary_db_columns(model_class):
""" Creates new table or relevant columns as necessary based on the model_class.
No columns or data are renamed or removed.
XXX: May need tweaking if db_column != field.name
"""
# Create table if missing
create_db_table(model_class)
# Add field columns if missing
table_name = model_class._meta.db_table
fields = [(f.column, f) for f in model_class._meta.fields]
db_column_names = [row[0] for row in connection.introspection.get_table_description(connection.cursor(), table_name)]
for column_name, field in fields:
if column_name not in db_column_names:
logging.debug("Adding field '%s' to table '%s'" % (column_name, table_name))
db.add_column(table_name, column_name, field)
And there you have it! You can call get_custom_car_model() to deliver a django model, which you can use to do normal django queries:
CarModel = get_custom_car_model(my_definition)
CarModel.objects.all()
Problems
Your models are hidden from Django until the code creating them is run. You can however run get_custom_car_model for every instance of your definitions in the class_prepared signal for your definition model.
ForeignKeys/ManyToManyFields may not work (I haven't tried)
You will want to use Django's model cache so you don't have to run queries and create the model every time you want to use this. I've left this out above for simplicity
You can get your dynamic models into the admin, but you'll need to dynamically create the admin class as well, and register/reregister/unregister appropriately using signals.
Overview
If you're fine with the added complication and problems, enjoy! One it's running, it works exactly as expected thanks to Django and Python's flexibility. You can feed your model into Django's ModelForm to let the user edit their instances, and perform queries using the database's fields directly. If there is anything you don't understand in the above, you're probably best off not taking this approach (I've intentionally not explained what some of the concepts are for beginners). Keep it Simple!
I really don't think many people need this, but I have used it myself, where we had lots of data in the tables and really, really needed to let the users customise the columns, which changed rarely.
Database
Consider your database design once more.
You should think in terms of how those objects that you want to represent relate to each other in the real world and then try to generalize those relations as much as you can, (so instead of saying each truck has a permit, you say each vehicle has an attribute which can be either a permit, load amount or whatever).
So lets try it:
If you say you have a vehicle and each vehicle can have many user specified attributes consider the following models:
class Attribute(models.Model):
type = models.CharField()
value = models.CharField()
class Vehicle(models.Model):
attribute = models.ManyToMany(Attribute)
As noted before, this is a general idea which enables you to add as much attributes to each vehicle as you want.
If you want specific set of attributes to be available to the user you can use choices in the Attribute.type field.
ATTRIBUTE_CHOICES = (
(1, 'Permit'),
(2, 'Manufacturer'),
)
class Attribute(models.Model):
type = models.CharField(max_length=1, choices=ATTRIBUTE_CHOICES)
value = models.CharField()
Now, perhaps you would want each vehicle sort to have it's own set of available attributes. This can be done by adding yet another model and set foreign key relations from both Vehicle and Attribute models to it.
class VehicleType(models.Model):
name = models.CharField()
class Attribute(models.Model):
vehicle_type = models.ForeigngKey(VehicleType)
type = models.CharField()
value = models.CharField()
class Vehicle(models.Model):
vehicle_type = models.ForeigngKey(VehicleType)
attribute = models.ManyToMany(Attribute)
This way you have a clear picture of how each attribute relates to some vehicle.
Forms
Basically, with this database design, you would require two forms for adding objects into the database. Specifically a model form for a vehicle and a model formset for attributes. You could use jQuery to dynamically add more items on the Attribute formset.
Note
You could also separate Attribute class to AttributeType and AttributeValue so you don't have redundant attribute types stored in your database or if you want to limit the attribute choices for the user but keep the ability to add more types with Django admin site.
To be totally cool, you could use autocomplete on your form to suggest existing attribute types to the user.
Hint: learn more about database normalization.
Other solutions
As suggested in the previous answer by Stuart Marsh
On the other hand you could hard code your models for each vehicle type so that each vehicle type is represented by the subclass of the base vehicle and each subclass can have its own specific attributes but that solutions is not very flexible (if you require flexibility).
You could also keep JSON representation of additional object attributes in one database field but I am not sure this would be helpfull when querying attributes.
Here is my simple test in django shell- I just typed in and it seems work fine-
In [25]: attributes = {
"__module__": "lekhoni.models",
"name": models.CharField(max_length=100),
"address": models.CharField(max_length=100),
}
In [26]: Person = type('Person', (models.Model,), attributes)
In [27]: Person
Out[27]: class 'lekhoni.models.Person'
In [28]: p1= Person()
In [29]: p1.name= 'manir'
In [30]: p1.save()
In [31]: Person.objects.a
Person.objects.aggregate Person.objects.all Person.objects.annotate
In [32]: Person.objects.all()
Out[33]: [Person: Person object]
It seems very simple- not sure why it should not be a considered an option- Reflection is very common is other languages like C# or Java- Anyway I am very new to django things-
Are you talking about in a front end interface, or in the Django admin?
You can't create real fields on the fly like that without a lot of work under the hood. Each model and field in Django has an associated table and column in the database. To add new fields usually requires either raw sql, or migrations using South.
From a front end interface, you could create pseudo fields, and store them in a json format in a single model field.
For example, create an other_data text field in the model. Then allow users to create fields, and store them like {'userfield':'userdata','mileage':54}
But I think if you're using a finite class like vehicles, you would create a base model with the basic vehicle characteristics, and then create models that inherits from the base model for each of the vehicle types.
class base_vehicle(models.Model):
color = models.CharField()
owner_name = models.CharField()
cost = models.DecimalField()
class car(base_vehicle):
mileage = models.IntegerField(default=0)
etc