How to set the default value for ForeignKey

Question

I have this field

graduation_year = m.ForeignKey('GraduationYear', on_delete=m.SET_NULL, null=False,blank=False)

and GraduationYear class is.

class GraduationYear(BaseModel):
    label = m.CharField(max_length=255)
    year = m.CharField(max_length=255,unique=True)
    def __str__(self):
        return self.label

Now I want to set the GraduationYear object where year=2022 as the default value of graduation_year

So, I am guessing I should embed sql to here below.

graduation_year = m.ForeignKey('GraduationYear', on_delete=m.SET_NULL, null=False,blank=False,default='select GraduationYear where year=2022')

Is it possible?

Does this answer your question? [Setting default value for Foreign Key attribute](https://stackoverflow.com/questions/9311996/setting-default-value-for-foreign-key-attribute) — Abdul Aziz Barkat, Nov 15 '22 at 07:35

ybl · Accepted Answer · 2022-11-17T08:57:01.557

If your table is only managed using the ORM, a good approach would be to override the save method on the model to set it if not provided:

class GraduationYear(BaseModel):
    label = m.CharField(max_length=255)
    year = m.CharField(max_length=255,unique=True)
    def __str__(self):
        return self.label


class GraduationDetails(BaseModel):
    graduation_year = m.ForeignKey('GraduationYear', on_delete=m.SET_NULL, null=False, blank=False)

    def save(self, *args, **kwargs):
        if not self.graduation_year:
            self.graudation_year, _ = GraduationYear.objects.get_or_create(year=2022)
        return super().save(*args, **kwargs)

It works perfect for my purpose. – whitebear Nov 16 '22 at 05:22 — whitebear, Nov 16 '22 at 05:22

score 0 · Answer 2 · edited Nov 15 '22 at 16:04

0

default=lambda: GraduationYear.objects.get_or_create(year=2022)[0]

edited Nov 15 '22 at 16:04

Tyler2P

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answered Nov 15 '22 at 07:31

İlyas Sarı

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Please consider adding some explanation to the source code explaining how it solves the problem. – Azhar Khan Nov 15 '22 at 08:39
Thank you for your comment.I use @ybl way for this problem. I appreciate your answer. – whitebear Nov 16 '22 at 05:25

How to set the default value for ForeignKey

2 Answers2