Merge branch 'master' into fix/field-mapping

# Conflicts:
#	formly/tests/tests.py

formly/fields.py

@@ -0,0 +1,25 @@
+from django import forms
+from django.core.exceptions import ValidationError
+from django.utils.translation import gettext_lazy as _
+
+
+class LimitedMultipleChoiceField(forms.MultipleChoiceField):
+    def __init__(self, *args, **kwargs):
+        self.maximum_choices = kwargs.pop("maximum_choices")
+
+        self.default_error_messages.update({
+            'maximum_choices': _('You may select at most %(maximum)d choices (%(selected)d selected)')
+        })
+
+        super(LimitedMultipleChoiceField, self).__init__(*args, **kwargs)
+
+    def validate(self, value):
+        super(LimitedMultipleChoiceField, self).validate(value)
+
+        selected_count = len(value)
+        if self.maximum_choices and selected_count > self.maximum_choices:
+            raise ValidationError(
+                self.error_messages['maximum_choices'],
+                code='maximum_choices',
+                params={'maximum': self.maximum_choices, 'selected': selected_count},
+            )

formly/models.py

@@ -12,6 +12,7 @@
 
 from jsonfield import JSONField
 
+from .fields import LimitedMultipleChoiceField
 from .forms import MultipleTextField, MultiTextWidget
 from .forms.widgets import LikertSelect, RatingSelect
 
@@ -362,6 +363,8 @@ def _get_field_class(self, choices):
 
         if self.field_type in [Field.CHECKBOX_FIELD, Field.SELECT_FIELD, Field.RADIO_CHOICES, Field.LIKERT_FIELD, Field.RATING_FIELD]:
             kwargs.update({"choices": choices})
+            if self.field_type == Field.CHECKBOX_FIELD:
+                kwargs.update({"maximum_choices": self.maximum_choices})
         elif self.field_type == Field.MULTIPLE_TEXT:
             kwargs.update({
                 "fields_length": self.expected_answers,
@@ -406,7 +409,7 @@ def _get_field_class(self, choices):
         )
     ),
     Field.CHECKBOX_FIELD: dict(
-        field_class=forms.MultipleChoiceField,
+        field_class=LimitedMultipleChoiceField,
         kwargs=dict(
             widget=forms.CheckboxSelectMultiple()
         )

formly/tests/tests.py

@@ -1,9 +1,11 @@
+from django.core.exceptions import ValidationError
 from django.contrib.auth import get_user_model
 from django.test import TestCase
 
 from ..models import (
     Field,
     Survey,
+    FieldChoice,
 )
 
 User = get_user_model()
@@ -44,3 +46,28 @@ def test_text_field_form_field_render(self):
         )
         # Ensure no exception when field is instantiated
         self.assertTrue(field.form_field())
+
+    def test_multiplechoice_field_choice_limit(self):
+        """
+        Enforce maximum_choices on multiple choice fields that allow
+        multiple answers.
+        """
+        survey = Survey.objects.create(
+            name="multiple choice test",
+            creator=self.user,
+        )
+        field = Field.objects.create(
+            survey=survey,
+            label="multiple choice field",
+            field_type=Field.CHECKBOX_FIELD,
+            maximum_choices=1,
+            ordinal=0,
+        )
+        choice_pks = []
+        for label in ["a", "b"]:
+            choice = FieldChoice.objects.create(label=label, field=field)
+            choice_pks.append(choice.pk)
+
+        form_field = field.form_field()
+        with self.assertRaises(ValidationError):
+            form_field.clean(choice_pks)