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How to make more than one fields primary key and remove auto generated id in django models

Suppose in a relational database schema we have a student, a subject and a teacher which connect to each other with a relation teaches. Also, the relation has an attribute time that stores the time of the lesson. This is the most complete yet simplified example I can think to describe my case. Now, the most pythonic and django-wise way I can think of trying to reach a correct solution is, after creating a model class for student, subject and teacher, to create a new class Teaches, which has the foreign keys for the three other classes; also it has the property date field for time. This class would look something like this:
class Teaches(models.Model):
teachers = models.ForeignKey(Teacher, on_delete_models.CASCADE)
subjects = models.ForeignKey(Subject, on_delete_models.CASCADE)
students = models.ForeignKey(Student, on_delete_models.CASCADE)
time = models.DateField
class Meta:
constraints = [
fields=['teachers', 'subjects', 'students']
name='teacher_subject_student_triplet'
]
I added the Meta class because this is what this answer recommends as the correct approach.
The problem is that that in the migrations file I can still see the id field. The only way I've seen there is to remove it is to set another field as Primary Key, but in my case I cannot do that, having more than one keys. Any suggestions?

=========== model.py =============
from django.db import models
class TeacherModel(models.Model):
teacher_code = models.CharField(max_length=255)
def __str__(self):
return self.teacher_code
class SubjectModel(models.Model):
subject_code = models.CharField(max_length=255)
def __str__(self):
return self.subject_code
class StudentModel(models.Model):
student_code = models.CharField(max_length=255)
def __str__(self):
return self.student_code
class Teaches(models.Model):
custom_primary_key = models.SlugField(primary_key=True,blank=True)
teacher = models.ForeignKey(TeacherModel, on_delete=models.CASCADE)
subject = models.ForeignKey(SubjectModel, on_delete=models.CASCADE)
student = models.ForeignKey(StudentModel, on_delete=models.CASCADE)
time = models.DateField
#property
def make_key(self):
new_key = str(self.teacher.teacher_code + self.subject.subject_code + self.student.student_code)
return new_key
def save(self, *args, **kwargs):
self.custom_primary_key = self.make_key
super(Teaches, self).save(*args, **kwargs)
========= Output ==============

You can remove autogenerated id by adding primary_key=True, see below code:
class Person(models.Model):
username = CharField(primary_key=True, max_length=100)
first_name = CharField(null=True, blank=True, max_length=100)
setting a field to primary_key=True automatically makes it unique and not null.

In settings.py:
DEFAULT_AUTO_FIELD = 'django.db.models.BigAutoField'
Controls the automatic generation of primary keys of each model if defined in settings.
Read this article:
Set AutoField or BigAutoField on a per model basis

django views, getting request and using it as a parameter

I'm very confused about this right now,
so I know when there's a simple code like the below
def text_detail(request ,course_pk, step_pk):
step = get_object_or_404(Text, course_id = course_pk, pk=step_pk)
course_pk and step_pk from the url, and those requests are set equal to course_id and pk here. but what I don't understand is what is course_id and pk here? I mean, course_id is from Course model which is foreignkey to step. so it's self.Course.id so it's course_id. But then, how about the next one pk? shouldn't it be step_id = step_pk? when it's just pk how does django know which pk it is?
Sorry if the question is very confusing, I'm very confused right now.
Edit
class Step(models.Model):
title = models.CharField(max_length=200)
description = models.CharField()
order = models.IntegerField(default=0)
course = models.ForeignKey(Course)
class Meta:
abstract = True
ordering = ['order',]
def __str__(self):
self.title
class Text(Step):
content = models.TextField(blank=True, default="")

Actually the get_or_404() method doing a similar/exact job as below,
try:
return Text.object.get(pk=step_pk,course_id = course_pk)
except Text.DoesNotExist:
raise Http404
You can read the source code of the same here
What is course_id and pk ?
Both are attributes of your Text model, as the name indicates pk is your Primary Key of Text model and course_id is the id/pk of course field which is a FK.
EDIT
Text is inherited from Step model so, it will show properties of usual python class.Hence, the Text model be like this internally (not-exact)
class Text(models.Model):
content = models.TextField(blank=True, default="")
title = models.CharField(max_length=200)
description = models.CharField()
order = models.IntegerField(default=0)
course = models.ForeignKey(Course)
class Meta:
ordering = ['order', ]
def __str__(self):
return self.title
Example
text = Text.objects.get(id=1) # text instance with id=1
text.course_id # will hold the id of "course" instance which is related to the particular "text" instance
URL assignment and all those stuffs are entirely depends on your choice and logic. So If you need to get a Text instance in your view, do as below,
text = get_object_or_404(Text, pk = pk_of_TEXT_instance)

django-tables 2 M2M field not shown

I am trying to show a M2M field in a django-table2 as seen in Django-tables2: How to use accessor to bring in foreign columns? and Accessing related models with django-tables2
Using: foreigncolumn = tables.Column(accessor='foreignmodel.foreigncolumnname'), I only see a '--'...
# The models:
class Organism(models.Model):
species_name = models.CharField(max_length=200)
strain_name = models.CharField(max_length=200)
eukaryotic = models.BooleanField(default=True)
lipids = models.ManyToManyField('Lipid',blank=True)
class Lipid(models.Model):
lm_id = models.CharField(max_length=100)
common_name = models.CharField(max_length=100,blank=True)
category = models.CharField(max_length=100,blank=True)
#The tables
class OrganismTable(tables.Table):
name = tables.LinkColumn('catalog:organism-detail', text=lambda record: record.species_name, args=[A('pk')])
lp = tables.Column(accessor='Lipid.common_name')
class Meta:
model = Organism
sequence = ['name','lp']
exclude = ['id','species_name']
Any idea what I'm doing wrong?

This does not work so easily for ManyToManyFields because of the simple way Accessor works. You could display the repr of the related QuerySet via 'lipids.all' but that does not seem sufficient here. You can, however, add a property (or method) to your Organism model and use it in the accessor. This way, you can display any custom information related to the instance:
class Organism(models.Model):
# ...
#property
def lipid_names(self):
return ', '.join(l.common_name for l in self.lipids.all()) # or similar
class OrganismTable(tables.Table):
# ...
lp = tables.Column(accessor='lipid_names')
I would recommend then to add a prefetch_related('lipids') to the Organism QuerySet that you pass to the table for better performance.

how to handle django many to many mapper object [duplicate]

This question already has an answer here:
Django: show list of many to many items in the admin interface
(1 answer)
Closed 9 years ago.
i have model :
class tags(models.Model):
""" This is the tag model """
tag = models.CharField(max_length=15) # Tag name
tagDescription = models.TextField() # Tag Description
tagSlug = models.CharField(max_length=400) # Extra info can be added to the existing tag using this field
createdAt = models.DateTimeField(auto_now_add=True)
updatedAt = models.DateTimeField(auto_now=True)
def __unicode__(self):
return unicode(self.tag)
class stores(models.Model):
""" This is the store model """
storeName = models.CharField(max_length=15) # Store Name
storeDescription = models.TextField() # Store Description
storeURL = models.URLField() # Store URL
storePopularityNumber = models.IntegerField(max_length=1) # Store Popularity Number
storeImage = models.ImageField(upload_to=storeImageDir) # Store Image
storeSlug = models.CharField(max_length=400) # This is the text you see in the URL
createdAt = models.DateTimeField(auto_now_add=True) # Time at which store is created
updatedAt = models.DateTimeField(auto_now=True) # Time at which store is updated
storeTags = models.ManyToManyField(tags) # All the tags associated with the store
def __unicode__(self):
return unicode(self.storeName)
def StoreTags(self):
return unicode(self.storeTags.all())
It is displaying [] under StoreTags
this is storesAdmin class:
class storesAdmin(admin.ModelAdmin):
list_display = ('storeName','storeDescription','storeURL',
'storePopularityNumber','storeImage',
'storeSlug','createdAt','createdAt','StoreTags'
)
Why it is displaying like that i even tried to convert it into unicode but it not working..

Avoid using CamelCase in Model Fields. Django Codigo Style - Model Field
"Field names should be all lowercase, using underscores instead of camelCase."
Avoid using CamelCase in functions and methods.
"Use underscores, not camelCase, for variable, function and method names (i.e. poll.get_unique_voters(), not poll.getUniqueVoters)."
Try choosing another name for storetags method. Maybe it clashes with storetags field name.django hash object

Try with code:
models
class Tags(models.Model):
#...
def __unicode__(self):
return '%s' % self.tag
class Stores(models.Model):
#...
def __unicode__(self):
return '%s' % self.storeTags.tag
admin, list_display is not supported to ManyToMany, i'm remove storetags
class storesAdmin(admin.ModelAdmin):
list_display = ('storename','storedescription','storeurl',
'storepopularitynumber','storeimage',
'storeslug','createdat','createdat'
)
Tell me if it works correctly.

How to store functions in django models

edit: I completely rewrote the question as the original one didn't clearly explain my question
I want to run a function which is specific to each particular model instance.
Ideally I want something like this:
class MyModel(models.Model):
data = models.CharField(max_length=100)
perform_unique_action = models.FunctionField() #stores a function specific to this instance
x = MyModel(data='originalx', perform_unique_action=func_for_x)
x.perform_unique_action() #will do whatever is specified for instance x
y = MyModel(data='originaly', perform_unique_action=func_for_y)
y.perform_unique_action() #will do whatever is specified for instance y
However there is no datatype FunctionField. Normally this would be solvable with inheritance, and creating subclasses of MyModel, maybe like this:
class MyModel(models.Model):
data = models.CharField(max_length=100)
perform_unique_action = default_function
class MyModelX(MyModel):
perform_unique_action = function_X
class MyModelY(MyModel):
perform_unique_action = function_Y
x = MyModelX(data='originalx')
x.perform_unique_action() #will do whatever is specified for instance x
y = MyModelY(data='originaly')
y.perform_unique_action() #will do whatever is specified for instance y
Unfortunately, I don't think I can use inheritance because I am trying to access the function this way:
class MyModel(models.Model):
data = models.CharField(max_length=100)
perform_unique_action = default_function
class SecondModel(models.Model):
other_data = models.IntegerField()
mymodel = models.ForeignKey(MyModel)
secondmodel = SecondModel.objects.get(other_data=3)
secondmodel.mymodel.perform_unique_action()
The problem seems to be that I don't know what type the foreign key is going to be in SecondModel if I override the perform_unique_action in subclasses.
Can I access MyModel from SecondModel as a foreign key and still have a unique function for each instance of MyModel?

This works for me. I haven't tested it, but you should be able to create another class and override their methods and it'll work. Check the class Meta line, it'll treat it as an abstract class. Here's an example of my actual classes that I'm working on right now.
EDIT: Added VoteComment class and tested it. It works as expected!
class Vote(models.Model):
VOTE_ENUM = (
(VoteEnum.DOWN_VOTE, VoteEnum.toString(VoteEnum.DOWN_VOTE)),
(VoteEnum.NONE, VoteEnum.toString(VoteEnum.NONE)),
(VoteEnum.UP_VOTE, VoteEnum.toString(VoteEnum.UP_VOTE)),
)
question = models.ForeignKey(Question, null=False, editable=False, blank=False)
voter = models.ForeignKey(User, blank=False, null=False, editable=False)
vote_type = models.SmallIntegerField(default=0, null=False, blank=False, choices=VOTE_ENUM)
class Meta:
abstract = True
def is_upvote(self):
return self.vote_type > 0
def is_downvote(self):
return self.vote_type < 0
class VoteAnswer(Vote):
answer = models.ForeignKey(Answer, null=False, editable=False, blank=False)
class Meta:
unique_together = (("voter", "answer"),) # to prevent user from voting on the same question/answer/comment again
def __unicode__(self):
vote_type = "UP" if vote_type > 0 else ("DOWN" if vote_type < 0 else "NONE")
return u"{0}: [{1}] {2}".format(user.username, vote_type, answer.text[:32])
def is_upvote(self):
return "FOO! "+str(super(VoteAnswer, self).is_upvote())
class VoteComment(Vote):
comment = models.ForeignKey(Comment, null=False, editable=False, blank=False)
class Meta:
unique_together = (("voter", "comment"),) # to prevent user from voting on the same question/answer/comment again
def __unicode__(self):
vote_type = "UP" if vote_type > 0 else ("DOWN" if vote_type < 0 else "NONE")
return u"{0}: [{1}] {2}".format(user.username, vote_type, comment.text[:32])
def is_upvote(self):
return "BAR!"

I came up with two ways of having a specific function defined for each object. One was using marshal to create bytecode which can be stored in the database (not a good way), and the other was by storing a reference to the function to be run, as suggested by Randall. Here is my solution using a stored reference:
class MyModel(models.Model):
data = models.CharField(max_length=100)
action_module = models.CharField(max_length=100)
action_function = models.CharField(max_length=100)
class SecondModel(models.Model):
other_data = models.IntegerField()
mymodel = models.ForeignKey(MyModel)
secondmodel_obj = SecondModel.objects.get(other_data=3)
#The goal is to run a function specific to the instance
#of MyModel referred to in secondmodel_obj
module_name = secondmodel_obj.mymodel.action_module
func_name = secondmodel_obj.mymodel.action_function
module = __import__(module_name)
func = vars(module)[func_name]
func()
Thanks to everyone who replied, I couldn't have got to this answer if it weren't for your help.

You could achive some similar behavior overriding the save method. And providing special callbacks to your instances.
Something like:
def default_function(instance):
#do something with the model instance
class ParentModel(model.Model):
data = models.CharField()
callback_function = default_function
def save(self, *args, **kwargs):
if hasattr(self, 'callback_function'):
self.callback_function(self)
super(ParentModel, self).save(*args, **kwargs)
class ChildModel():
different_data = models.CharField()
callback_function = other_fun_specific_to_this_model
instance = ChildModel()
#Specific function to this particular instance
instance.callback_function = lambda inst: print inst.different_data
instance.save()

You can write endpoints on your server and limit their access to just your self. Then store in each model instance corresponding url. For example:
views.py
def funx_x(request):
pass
def func_y(request):
pass
models.py:
class MyModel(models.Model):
data = models.CharField(max_length=100)
perform_unique_action = models.URLField()
and then:
x = MyModel(data='originalx', perform_unique_action='http://localhost/funx_x')
requests.post(x.perform_unique_action)

i dont know whether i understand u correct or not. but you can check out this example here.
Example:
A string representing an attribute on the model. This behaves almost the same as the callable, but self in this context is the model instance. Here's a full model example:
class Person(models.Model):
name = models.CharField(max_length=50)
birthday = models.DateField()
def decade_born_in(self):
return self.birthday.strftime('%Y')[:3] + "0's"
decade_born_in.short_description = 'Birth decade'
class PersonAdmin(admin.ModelAdmin):
list_display = ('name', 'decade_born_in')