Django multiple choice and multi-select field in model and form - django

Question

I am learning Django and have hit an inssue that I don't know what to Google for. I have the standard User model and a Profile model that points into the User model via a OneToOne field. That part plus the profile's Form and the CBVs all work.
A profile holder can have one or more professional affiliations. This is not for a union but my Dad, for example, as a welder, was affiliated with: "The Iron Workers", "Steam Fitters", "Boiler Makers", "Pipe Fitters" and a couple other specific unions that used welders. So if I want the profile and form to allow multiple choices and multiple selected results for affiliations then I see that you might use
class Profile(models.Model):
GROUPS = (
('IW', 'Iron Workers'),
('PF', 'Pipe Fitters'),
...
)
affiliation = models.CharField(
max_length=3,
choices=RANK,
default='U',
blank=True,
null=True,
)
...
In the associated form it looks like you use a
GROUPS = (
('IW', 'Iron Workers'),
('PF', 'Pipe Fitters'),
...
)
affiliation = forms.MultipleChoiceField(
choices=GROUPS
)
What if I want a db table of these choice items instead of tuples? If I have to add to a list of choices then editing the code might not be the most convenient response. Maybe the list of groups should be in the Django admin area.
How do I tell the model and form to look in a separate db table for the possible values and then how do I modify the model and form to allow for zero or more group affiliations?

Answer 1

You need to create a many-to-many relationship to a new model, let's call it Skill, that represents the available skills that can be dynamically created.
class Profile(models.Model):
# ...
skills = models.ManyToManyField(
to='myapp.Skill', # use a string in the format `app_name.model_name` to reference models to avoid issues using the model before it was defined
related_name='user_profiles', # the name for that relation from the point of view of a skill
)
class Skill(models.Model):
name = models.CharField(max_length=255)
abbreviation = models.CharField(max_length=3)
Then in your form you can just add that many-to-many field skills. It will by default be a multiple choice field in the django admin.
The relation can have zero to n entries for each pair of profile and skill. In other words, every user can have zero to n skills and vice versa.
To allow for a default value you will have to write a custom migration that creates that default entity of a Skill to make sure it is in the database at runtime.

Answer 2

In my case, I solved this way with a select2 list option.
It returns in the view a list of option selected.
FORMS
class PrecoattivoForm(forms.Form):
entrate = AccertamentiEnte.objects.all().values("entrata_provvedimento").distinct()
lista = []
for i in entrate:
lista.append([i.get('entrata_provvedimento'),i.get('entrata_provvedimento')])
entrata_accertamento= forms.MultipleChoiceField(choices=lista, required=False)
TEMPLATE
<div class="col-xl-10">
<selectclass="js-example-placeholder-multiple col-sm-12"
multiple="multiple"
name="{{ form.entrata_accertamento.name }}"
id="{{ form.entrata_accertamento.id_for_label }}">
{% for entrata in form.entrata_accertamento %}
<option {% if form.name.value != None %}value="
{{form.entrata_accertamento.value|upper }}"{% endif %}>{{ entrata }}</option>
{% endfor %}
</select>
</div>