Django ModelForm: How to Add ForeignKey as Field in Form?

I have Three Models StudentInfo, StdSubject, Marks

class StdSubject(StdCommon):
REGULAR='R'
OPTIONAL='O'

SUBJECT_TYPE_CHOICE=(
(REGULAR, 'REGULAR'),
(OPTIONAL, 'OPTIONAL')
)


subject_name = models.CharField('Subject Name', max_length=100)
subject_type = models.CharField(
'Subject Type', max_length=1, default=REGULAR, choices=SUBJECT_TYPE_CHOICE)
subject_full_marks = models.DecimalField(
'Full Marks', max_digits=5, decimal_places=2, default=100)
subject_pass_marks = models.DecimalField(
'Pass Marks', max_digits=5, decimal_places=2)


def __str__(self):
return self.subject_name


class StudentInfo(StdCommon):
STD_CLASS=(
('6','Six'),
('7','Seven'),
('8','Eight'),
('9','Nine'),
('10','Ten'),
)

STD_GENDER=(
('MALE','Male'),
('FEMALE','Female'),
)

STD_GROUP=(
('S', 'Science'),
('B', 'Business Studies'),
('H', 'Humatics'),
('G', 'General')
)

std_name = models.CharField('Student Name',max_length=100, help_text='Type only student Full Name like as Nazmul Islam or Nazrul Islam')
std_class = models.CharField('Student Class',max_length=2, choices=STD_CLASS, default=6, help_text='Select a class')
std_roll = models.IntegerField('Roll Number',help_text='Type Student Roll Number (Only Number)')
std_group=models.CharField('Group', choices=STD_GROUP, max_length=1, default='G')
std_gender=models.CharField('Gender', max_length=10, choices=STD_GENDER, default='MALE')
std_subjects = models.ManyToManyField(StdSubject)

def __str__(self):
return self.std_name





class Marks(StdCommon):
std_name=models.ForeignKey(StudentInfo, on_delete=models.CASCADE)
subject_name = models.ForeignKey(StdSubject, on_delete=models.CASCADE)
subject_marks=models.DecimalField(max_digits=5, decimal_places=2, help_text='Please give proper number')

subject_gradepoint=models.DecimalField('Grade Point', max_digits=3, decimal_places=1, blank=True, null=True, help_text="Please keep blank")
subject_gpa = models.CharField('Subject GPA', max_length=5, blank=True, null=True, help_text="Please keep blank")
std_result=models.FloatField(blank=True, null=True)



def __str__(self):
return self.std_name.std_name+' Class: '+str(self.std_name.std_class)+' Roll: '+str(self.std_name.std_roll) +' ' + self.subject_name.subject_name +' '+str(self.subject_marks)



def subject_grade(self):
grade = SubjectGrade(self.subject_marks,self.subject_name.subject_full_marks).subgrade()
return grade

def subject_grade_point(self):
grade = SubjectGradePoint( self.subject_marks, self.subject_name.subject_full_marks).subgrade()
return grade


def save(self, *args, **kwargs):
grade_point = SubjectGradePoint(self.subject_marks, self.subject_name.subject_full_marks).subgrade()
gpa = SubjectGrade(self.subject_marks,self.subject_name.subject_full_marks).subgrade()

if self.subject_name.subject_type=='O':
if self.subject_marks >= ((self.subject_name.subject_full_marks/100)*50) and self.subject_marks <= self.subject_name.subject_full_marks:
subject_opt_grade_point = grade_point-2

self.subject_gradepoint = subject_opt_grade_point
self.subject_gpa = gpa
elif self.subject_marks >= ((self.subject_name.subject_full_marks/100)*33) and self.subject_marks < ((self.subject_name.subject_full_marks/100)*50):
self.subject_gradepoint = 0
self.subject_gpa=gpa

elif self.subject_marks < ((self.subject_name.subject_full_marks/100)*33):
self.subject_gradepoint = 0
self.subject_gpa = gpa


elif self.subject_name.subject_type=='R':
self.subject_gradepoint = grade_point
self.subject_gpa = gpa

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


I created a Form like this

class StudentSubjectGPAFormAdd(forms.ModelForm):
class Meta:
model = Marks
exclude = ('std_name','subject_gpa',
'subject_gradepoint', 'std_result')

def __init__(self, *args, **kwargs):
super(IncomingForm, self).__init__(*args, **kwargs)
if self.instance:
self.fields['subject_marks'].queryset = StudentInfo.objects.filter(
std_name__exact=self.instance.id)


When I go to my student profile I want to add student subject marks. But It cant work. But It should be follow this lineup

Just I will select subject and input marks then save.

I want to add student marks like as this image

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