Django: Display inline through direct relation

Question

I have models:

class CustomUser(AbstractUser):
    employee_number = models.CharField(max_length=255, blank=True, db_index=True)
    position = models.ForeignKey(
        'orgunits.Position',
        on_delete=models.CASCADE,
        related_name='employees'
    )


class Position(models.Model):
    orgunit = models.ForeignKey(
        OrgUnit,
        on_delete=models.CASCADE,
        verbose_name=_('orgunit'),
        related_name='positions',
    )
    name = models.CharField(_('name'), max_length=255)


class OrgUnit(models.Model):
    name = models.CharField(_('name'), max_length=255)
    type = models.CharField(_('type'), max_length=55)
    address = models.TextField(_('address'), null=True, blank=True)

I would like to display all CustomUser instances assigned to OrgUnit THROUGH Position:

class OrgUnitEmployeesInline(admin.TabularInline):
    model = CustomUser


class OrgUnitAdmin(admin.ModelAdmin):
    model = OrgUnit
    inlines = OrgUnitEmployeesInline,

But of course there is an error:

<class 'orgunits.admin.OrgUnitEmployeesInline'>: (admin.E202) 'authentication.CustomUser' has no ForeignKey to 'orgunits.OrgUnit'.

because Position has ForeignKey to 'orgunits.OrgUnit'.

Also I tried this:

class OrgUnitEmployeesInline(admin.TabularInline):
    model = CustomUser
    fk_name = 'position'

but error:

<class 'orgunits.admin.OrgUnitEmployeesInline'>: (admin.E202) fk_name 'position' is not a ForeignKey to 'orgunits.OrgUnit'.

How can I display users in orgunits inline?

Answer 1

The closest thing in simple way is this:

class OrgUnitEmployeesInline(admin.TabularInline):
    model = Position
    fk_name = 'positions'
    fields = ('employees', )

Otherwise you have to settle with custom forms.