Save a foreign key in postgreSQL using python-django - django

Question

I'm trying to a save a foreign key inside an object into my db using a form, but i get the error : 'Syntax isn't valid for integer', I discovered that postgreSQL save the foreign key as an id, how can i save it then?
Here it is my code.
Models.py :
class treballador(models.Model):
nom = models.CharField(max_length=150, null=False, unique=True)
cognom = models.CharField(max_length=150, null=False)
tipusDocID = models.CharField(max_length=3, choices=TIPUSDOC, null=False)
docId = models.CharField(max_length=9, null=False)
tlf_regex = RegexValidator(regex=r'^\d{9,9}$',message="Phone number must be entered in the format: '[phone]'. Up to 9 digits allowed.")
tlf = models.CharField(validators=[tlf_regex], blank=True, max_length=9) # validators should be a list
correu = models.EmailField(max_length=254)
ciutat = models.CharField(max_length=150)
dataDAlta = models.DateTimeField(auto_now_add=True)
def __unicode__(self):
return unicode(self.nom) or unicode(self.id)
class despesa(models.Model):
nomTreballador = models.ForeignKey(treballador, to_field='nom')
tipusDeGast = models.CharField(max_length=3, choices=GASTOS)
quantia = models.DecimalField(max_digits=5, decimal_places=2)
data = models.DateTimeField()
forms.py:
class desModelForm(forms.ModelForm):
data = forms.DateField(widget=DateInput(format='%d/%m/%Y'), label="Data de la despesa", input_formats=['%d/%m/%Y'])
class Meta:
model= despesa
fields= ["nomTreballador","tipusDeGast","quantia","data"]
def clean_despesa(self):
despeses = self.cleaned_data.get("tipusDeGast")
return despeses
def clean_date(self):
date = self.cleaned_data.get("data")
return date
def clean_quantia(self):
quantia = self.cleaned_data.get("quantia")
return quantia
def clean_nom(self):
nomTreballador = self.cleaned_data.get("nomTreballador")
return nomTreballador
def __init__(self, *args, **kwargs):
super(desModelForm, self).__init__(*args, **kwargs)
self.fields["nomTreballador"].queryset=treballador.objects.all().distinct()
views.py:
def home(request):
form = desModelForm(request.POST or None)
context = {
"gast_form": form
}
if form.is_valid():
desp = form.save(commit=False)
desp.save()
return render(request, "imputacioDespeses.html", context)

Answer 1

Your foreign key field is the problem.
Remove to_field and Django will automatically map it to ID
nomTreballador = models.ForeignKey(treballador)

Answer 2

Remove to_field='nom' from the nomTreballador ForeignKey field and it will insert the Treballador's primary key (an integer) instead of nom (which is a string).