Fetching Updates Since Your Original Export

A common need is to be able to get all the updates since the last time you exported. That’s easy!

Simply pass --since=auto (to automatically detect the timestamp of your last export) or with a manual timestamp like --since=2025-02-10T10:23:54Z.

This will only export the resources that have changed since that time.

How it Works

Under the covers, SMART Fetch is just passing the server _since (in bulk mode) or _lastUpdated (in crawl mode) parameters.

If you provide a date, that is passed on directly. If you provide auto, SMART Fetch will look in the metadata it stores alongside your previous exports and pull out a date to use.

Vendors that Don’t Support Update Times

Some vendors don’t support the meta.lastUpdated field. In which case, they won’t support --since by default.

But that’s OK! If you pass in --since-mode=created, SMART Fetch will use an alternative “since” check.

Instead of using a “when was this resource last updated” check, it will use a “when was this resource created” check, for resources that have a “created” timestamp field.

Created mode is the default for servers that don’t declare support for the _lastUpdated search field (Epic is a notable example).

Limitations

This mode has severe limitations that discourage its use unless you have no other choice.

Possibility of Missed Resources

Most FHIR resource types have a “created time” field for SMART Fetch to search over.

But sometimes it’s more of a clinical date than an administrative date. For example, the only searchable date field for Observations is the effective choice field.

This means that if a newly created resource is clinically back-dated to before your since date, you will miss it.

For example, if an Observation is created today, but is marked with an effective date of three days ago, and you passed in a --since date of yesterday, that resource will not be picked up even though you would want it to be.

Resource types affected by this:

• Encounter
• Immunization
• Observation
• Procedure

Some Resources Have No Searchable Dates

Some resource types don’t even have searchable creation or clinical dates. SMART Fetch must export all of them every time. Thankfully, these resource types are not often huge. But it’s something to be aware of.

Resource types affected by this:

• Device
• Patient

Updates to Existing Resources Are Never Noticed

If an already-created resource has edits made to it, this method will not pick that up.

If this is critical, you may need to just do an entirely new export of all resources when you need to check for updates.