# How can I track uploads for a specific user?

Transloadit does not offer an explicit means to keep track of who of your users submitted a specific
file. However, we offer something much more flexible than that.

We allow you to add custom data to your <dfn>Assemblies</dfn> in the form of fields. For example,
you can add a hidden field `user_id` to your form, populate its value attribute accordingly, and
then set [Uppy Transloadit Form's](https://uppy.io/docs/transloadit/#waitForEncoding-false) `fields`
parameter to include the field.

This field will then become available in your <dfn>Assembly</dfn> as `${fields.user_id}` and will
also be appended to a `fields` array in the JSON response for you to save in your database.

You can read more about custom fields in <dfn>Assemblies</dfn>
[here](/docs/topics/templates.md#overruling-templates-at-runtime).