Trying to trigger a bulkcreation of records using a reverse relationship

[DumbaClassics]

Hello Family may you help. 

I am trying to create a School Attendance Module and I have a StudentClass table, the Student table, Attendance table and the AttendanceRecord table. Here is the code

class StudentClass(models.Model):

    name  =   models.CharField(max_length=100)

    # stream   =   models.ForeignKey('Stream', on_delete=models.PROTECT) 

    creation_date =   models.DateTimeField(auto_now=False, auto_now_add=True)

    def __str__(self):

        return self.name

class Student(models.Model):

name = models.CharField(max_length=100)

klass = models.ForeignKey('StudentClass', models.PROTECT, related_name='students')

def __str__(self):

return self.name

class Attendance(models.Model):

date = models.DateTimeField(auto_now_add=True)

klass = models.ForeignKey('StudentClass', models.PROTECT, related_name='attendances')

def save(self, *args, **kwargs):

if self.records.count() <= 0:

for student in self.klass.students.all():

self.records.create(student=student, status='present')

super(Attendance, self).save(*args, **kwargs)

def __str__(self):

return f"{self.id}, {self.date}"

class AttendanceRecord(models.Model):

ATTENDANCE_STATUS = [

('present', 'PRESENT'),

('absent', 'ABSENT')

]

attendance = models.ForeignKey(

'Attendance', 

on_delete=models.SET_NULL, 

null=True, 

blank=True,

related_name='records'

)

student = models.ForeignKey('Student', on_delete=models.PROTECT)

status = models.CharField(max_length=100, choices=ATTENDANCE_STATUS)

def __str__(self):

return f"(STUDENT: {self.student}, STATUS: {self.status})"

What am I trying to achieve??

I want to have a situation whereby when I trigger the creation of a Attendance instance an Attendance Record linked to that instance is generated with the record generating default attendance records for all students enrolled in that klass with a default attendance status of present which I can get on to edit only for those students who are absent. The method I tried for ovveriding the save method didnt work as it generated this error '    "unsaved related object '%s'." % field.name

ValueError: save() prohibited to prevent data loss due to unsaved related object 'attendance'.'

I wasnt really confident of that solution anyway. 

May you assist me on how best one wld solve such a problem

Thank you in Advance 

Dumba

[Chetan Ganji]

Im not 100% sure about this :P 

Instead of this -

def save(self, *args, **kwargs):

if self.records.count() <= 0:

for student in self.klass.students.all():

self.records.create(student=student, status='present')

super(Attendance, self).save(*args, **kwargs)

Try with below code - 

def save(self, *args, **kwargs):

super(Attendance, self).save(*args, **kwargs)

if self.records.count() <= 0:

for student in self.klass.students.all():

self.records.create(student=student, status='present') # separate sql query i guess for each entry created.

There is a diff logic. 

1. create attendance object.

2. bulk create AttendanceRecord objects 

https://docs.djangoproject.com/en/3.1/ref/models/querysets/#bulk-create

P.S. both of this operations should happen inside a transaction. 

https://docs.djangoproject.com/en/3.1/topics/db/transactions/

Regards,

Chetan Ganji

+91-900-483-4183

ganji....@gmail.com

http://ryucoder.in

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[Dumba Classics]

thank you @Chetan the solution does work and I am very grateful!!!!!!

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[Chetan Ganji]

Welcome :) 

Regards,

Chetan Ganji

+91-900-483-4183

ganji....@gmail.com

http://ryucoder.in

To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/CAMLk3fynHELM5My2mkzzPGo4moAYoU0d7XR0umhzKzbSKPaLSw%40mail.gmail.com.