Provide download link for part attachments

- Better upload management for attachment files (separated based on part ID)

InvenTree/part/models.py

@@ -372,15 +372,8 @@ class Part(models.Model):
 
 
 def attach_file(instance, filename):
-
-    base = 'part_files'
-
-    # TODO - For a new PartAttachment object, PK is NULL!!
-
-    # Prefix the attachment ID to the filename
-    fn = "{id}_{fn}".format(id=instance.pk, fn=filename)
-
-    return os.path.join(base, fn)
+    # Construct a path to store a file attachment
+    return os.path.join('part_files', str(instance.part.id), filename)
 
 
 class PartAttachment(models.Model):
@@ -393,6 +386,10 @@ class PartAttachment(models.Model):
 
     attachment = models.FileField(upload_to=attach_file, null=True, blank=True)
 
+    @property
+    def basename(self):
+        return os.path.basename(self.attachment.name)
+
 
 class BomItem(models.Model):
     """ A BomItem links a part to its component items.

InvenTree/part/templates/part/part_base.html

@@ -66,7 +66,7 @@
     <h4>Attachments</h4>
     <ul>
     {% for attachment in part.attachments.all %}
-    <li><a href="{{ attachment.attachment }}">{{ attachment.attachment }}</a></li>
+    <li><a href="/media/{{ attachment.attachment }}">{{ attachment.basename }}</a></li>
     {% endfor %}
     </ul>
 </div>