#22741: Migrate fails with `TypeError` when using a callable default for a
`ForeignKey`
-------------------------------------+-------------------------------------
Reporter: rednaw | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution: needsinfo
Keywords: migrations | Triage Stage:
foreignkey | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Description changed by timgraham:
Old description:
> When using a lambda function as a default value for a ForeignKey field,
> `makemigrations` will fail with the exception:
>
> ValueError: Cannot serialize function: lambda
>
> This is the code:
>
> from django.db import models
>
> class House(models.Model):
> address = models.CharField(max_length=100)
>
> class Person(models.Model):
> house = models.ForeignKey(House, default=lambda:
> House.objects.all()[0])
> name = models.CharField(max_length=100)
>
> I tried to change the lambda to a defined function like this:
>
> from django.db import models
>
> class House(models.Model):
> address = models.CharField(max_length=100)
>
> def first_house():
> House.objects.all()[0]
>
> class Person(models.Model):
> house = models.ForeignKey(House, default=first_house)
> name = models.CharField(max_length=100)
>
> In this case, `makemigrations` works, but `migrate` will now fail, with
> the exception:
>
> TypeError: int() argument must be a string or a number, not 'House'
>
> I'm testing this in Python 3 btw.
New description:
When using a lambda function as a default value for a ForeignKey field,
`makemigrations` will fail with the exception:
{{{
ValueError: Cannot serialize function: lambda
}}}
This is the code:
{{{
from django.db import models
class House(models.Model):
address = models.CharField(max_length=100)
class Person(models.Model):
house = models.ForeignKey(House, default=lambda:
House.objects.all()[0])
name = models.CharField(max_length=100)
}}}
I tried to change the lambda to a defined function like this:
{{{
from django.db import models
class House(models.Model):
address = models.CharField(max_length=100)
def first_house():
House.objects.all()[0]
class Person(models.Model):
house = models.ForeignKey(House, default=first_house)
name = models.CharField(max_length=100)
}}}
In this case, `makemigrations` works, but `migrate` will now fail, with
the exception:
{{{
TypeError: int() argument must be a string or a number, not 'House'
}}}
I'm testing this in Python 3 btw.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/22741#comment:2>
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