Find and Create-If-Necessary via REST API

Tips & Tricks
1

Simple Approach - find/get → if (missing) → create

At first it seems like the logic to branch and create a “record” should be simple and straightforward as:

  1. Find (REST GET)
  2. if exists, continue, else create then continue

Challenges in n8n

  • how to retain the input-item details (from before the REST call and/or found vs. created branches)
  • how to keep the items in the original order
  • how to wait until all items have either been found or created before continuing

Why so complex?

  • Sometimes, it can be simple, if you are using a DB node or REST API that is designed to always give you a response (output item) whether or not it finds something, but if an HTTP node returns a 404 - not found the output item count is different.
  • If the workflow then branches to the true/false outputs of an If node, timing and processing order might yield output items in a different order, making it necessary to re-correlate items on some key value.

Solution (one at least)

After struggling for a while with this task to import products and categories into Wordpress / WooCommerce, I reached a somewhat reliable approach to “conditionally create” things before continuing to create other dependent things. This workflow demonstrates the main elements, which are:

  • All original items, are forwarded to a final merge to be “enriched” by other found (existing) or created info. This preserves the original item order and retains all items.
  • Items “not found” using the GET REST call are “output anyway” from an HTTP Request node by using the “Never Error” option (and dealing with the actual non-404 errors separately).
  • Edit Fields (set) nodes are used to homogenize the output field names from GET vs. POST REST API calls, AND to forward a field/value (using item-linking) that can be used to correlate to the original input items.