Validating dynamically created ModelForm field in Django 2 - django

Question

I am using Django 2.0 and I have a model for Articles and a model for Storylines. A storyline contains many related articles.
class Article(models.Model):
headline_text = models.CharField(max_length=255, verbose_name='Headline')
storylines = models.ManyToManyField(Storyline, verbose_name='Add to Storylines')
I have a ModelForm that will allow you to choose an article to add to the Storyline. That ModelForm class looks like this:
class StorylineAddArticleForm(forms.Form):
articleSearchBox = forms.CharField(label="Search to narrow list below:")
include_articles = [article.id for article in Article.objects.order_by('-sub_date')[:5]]
articles = forms.ModelMultipleChoiceField(queryset=Article.objects.filter(id__in=include_articles).order_by('-sub_date'))
def __init__(self, *args, **kwargs):
super(StorylineAddArticleForm, self).__init__(*args, **kwargs)
self.fields['articleSearchBox'].required = False
self.helper = FormHelper(self)
self.helper.layout = Layout(
Field('articleSearchBox'),
Field('articles'),
ButtonHolder(
Submit('submit', 'Add', css_class='button white')
)
)
So far so good, if I submit any article in the queryset, the form validates and saves as needed.
The live site will have many more articles than will be practical to display in the ModelMultipleChoice field, so I do some JQuery to allow the user to use articleSearchBox to replace the ModelMultipleChoice field. This works brilliantly and you can do a search for any article, including those not in the original queryset. Here's that:
{% block content %}
<h2>Add Article</h2>
Add an existing article to <strong>{{ storyline.headline_text }}</strong> storyline:<br>
Did you want to add a new article instead?<br>
<hr>
{% crispy form %}
{% endblock %}
{% block pagescripts %}
<script>
$(document).ready(function(){
$("#id_articleSearchBox").on('input propertychange paste', function(){
$.ajax({
url:'/webproxy/a/?q=' + $("#id_articleSearchBox").val(),
type:'get',
dataType:'html',
crossDomain:true,
success:function(data)
{
$("#id_articles").empty().append(data);
},
error: function(data) {
$("#id_articles").empty().append("<option value=\"-1\">No results</option>");
}
});
}); // end article search box
});
</script>
{% endblock %}
THE PROBLEM:
If I do a search and get an article that was not in the original queryset, the validation fails and I am told that it is not a valid choice. I need a validator that will allow any article or articles, as long as they are actually in the database.
WHAT I HAVE TRIED:
I tried creating a validator that looks like this:
def clean_article(self):
art_ID = self.cleaned_data.get('articles', False)
if(art_ID):
try:
art = Article.objects.get(pk=art_ID)
except ObjectDoesNotExist:
return None
else:
return None
# if we are here, we have an article.
return art
This produced no change in behavior. I have looked and looked for a validator that would even allow any value or just check if it exists, but I am not having a lot of luck.

Answer 1

Your custom validator doesn't have any effect as it will be called after the field's validation. For more information about the order validations are run in refer to the django docs.
What you can do instead is overriding said field validation by inheriting from Django's MultipleChoiceField:
from django import forms
class ArticleMultipleChoiceField(forms.MultipleChoiceField):
def validate(self, value):
pass # your custom validation
You will then of course have to use your custom ArticleMultipleChoiceField in your StorylineAddArticleForm for the articles field.