Alternative field for many-to-many relationship, appears as list of

checkboxes

flask_admin/contrib/sqla/fields.py

@@ -13,6 +13,7 @@ except ImportError:
 
 from .tools import get_primary_key
 from flask_admin._compat import text_type, string_types, iteritems
+from flask_admin.contrib.sqla.widgets import CheckboxListInput
 from flask_admin.form import FormOpts, BaseForm, Select2Widget
 from flask_admin.model.fields import InlineFieldList, InlineModelFormField
 from flask_admin.babel import lazy_gettext
@@ -181,6 +182,30 @@ class QuerySelectMultipleField(QuerySelectField):
                     raise ValidationError(self.gettext(u'Not a valid choice'))
 
 
+class CheckboxListField(QuerySelectMultipleField):
+    """
+    Alternative field for many-to-many relationships.
+
+    Can be used instead of `QuerySelectMultipleField`.
+    Appears as the list of checkboxes.
+    Example::
+
+        class MyView(ModelView):
+            form_columns = (
+                'languages',
+            )
+            form_args = {
+                'languages': {
+                    'query_factory': Language.query,
+                },
+            }
+            form_overrides = {
+                'languages': CheckboxListField,
+            }
+    """
+    widget = CheckboxListInput()
+
+
 class HstoreForm(BaseForm):
     """ Form used in InlineFormField/InlineHstoreList for HSTORE columns """
     key = StringField(lazy_gettext('Key'))

flask_admin/contrib/sqla/widgets.py

+from wtforms.widgets.core import HTMLString, escape_html
+
+
+class CheckboxListInput:
+    """
+    Alternative widget for many-to-many relationships.
+
+    Appears as the list of checkboxes.
+    """
+    template = (
+        '<div class="checkbox">'
+        ' <label>'
+        '  <input id="%(id)s" name="%(name)s" value="%(id)s" '
+        'type="checkbox"%(selected)s>%(label)s'
+        ' </label>'
+        '</div>'
+    )
+
+    def __call__(self, field, **kwargs):
+        items = []
+        for val, label, selected in field.iter_choices():
+            args = {
+                'id': val,
+                'name': field.name,
+                'label': escape_html(label, quote=False),
+                'selected': ' checked' if selected else '',
+            }
+            items.append(self.template % args)
+        return HTMLString(''.join(items))