Django ModelForm not storing foreignkey in modeladmin - django

Question

I have the following code which is supposed to create a MyConfig object. However, it doesn't as the app_model is always returned as None.
The idea is to choose from a select few contenttypes and then add a key, and the resulting config will trigger a bunch of services. However whenever I save the form, the contenttype stored in the app_model is always None, which is clearly undesirable.
This is in Django1.8
Here is the admin:
class ContentTypeModelChoiceField(ModelChoiceField):
def label_from_instance(self, obj):
return "{}-{}".format(obj.app_label, obj.model)
class MyConfigForm(ModelForm):
class Meta:
model = models.MyConfig
fields = '__all__'
def __init__(self, *args, **kwargs):
super(MyConfigForm, self).__init__(*args, **kwargs)
self.fields['app_model'].label = "App Name"
app_model = ContentTypeModelChoiceField(
ContentType.objects.filter(
app_label__startswith='myApp',
model="myModel",
),
empty_label="Choose a model",
)
class MyConfigAdmin(admin.ModelAdmin):
model = models.MyConfig
form = MyConfigForm
list_display = (<display fields>
)
search_fields = (<search fields>
)
excluded_fields = ('app_model')
And here is the model itself:
class MyConfig(models.Model):
app_model = models.ForeignKey(ContentType, null=True)
ref_key = models.CharField(max_length=32, null=True)

Answer 1

To unfortunately somewhat have my tail between my legs. The missing code was the excluded_fields which contained app_model. I thought this removed it from the displayed fields, but it actually removes it from the data you save into the model upon save.
Thanks to everyone who looked into this. Many apologies.