Create a custom URL field, which allows the user-specified validators

- Ref: https://stackoverflow.com/questions/41756572/django-urlfield-with-custom-scheme
- Apply this to the URL field in the Part model

InvenTree/InvenTree/fields.py

@@ -0,0 +1,27 @@
+""" Custom fields used in InvenTree """
+
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from .validators import allowable_url_schemes
+
+from django.forms.fields import URLField as FormURLField
+from django.db import models as models
+from django.core import validators
+
+
+class InvenTreeURLFormField(FormURLField):
+    """ Custom URL form field with custom scheme validators """
+
+    default_validators = [validators.URLValidator(schemes=allowable_url_schemes())]
+
+
+class InvenTreeURLField(models.URLField):
+    """ Custom URL field which has custom scheme validators """
+
+    default_validators = [validators.URLValidator(schemes=allowable_url_schemes())]
+
+    def formfield(self, **kwargs):
+        return super().formfield(**{
+            'form_class': InvenTreeURLFormField
+        })

InvenTree/part/migrations/0023_auto_20190913_1401.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2.5 on 2019-09-13 14:01
+
+import InvenTree.fields
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('part', '0022_auto_20190908_0918'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='part',
+            name='URL',
+            field=InvenTree.fields.InvenTreeURLField(blank=True, help_text='Link to extenal URL'),
+        ),
+    ]

InvenTree/part/models.py

@@ -34,6 +34,7 @@ import hashlib
 from InvenTree import helpers
 from InvenTree import validators
 from InvenTree.models import InvenTreeTree
+from InvenTree.fields import InvenTreeURLField
 
 from InvenTree.status_codes import BuildStatus, StockStatus, OrderStatus
 
@@ -353,7 +354,7 @@ class Part(models.Model):
 
     revision = models.CharField(max_length=100, blank=True, help_text='Part revision or version number')
 
-    URL = models.URLField(blank=True, help_text='Link to extenal URL')
+    URL = InvenTreeURLField(blank=True, help_text='Link to extenal URL')
 
     image = models.ImageField(upload_to=rename_part_image, max_length=255, null=True, blank=True)