How can I aggregate and format compare datasets output into one email in n8n?

Based on your description, your goal is to aggregate the results of the compare datasets node into one consolidated string (or similar data structure) so that the Gmail node sends a single email with the list of animals that are out of sync.

In n8n, each node’s output is an array of items. If you simply pass that data directly to the Gmail node, n8n will usually treat each item separately. Since you can’t create a for loop directly in an expression, you’ll need a node that aggregates the multiple items into a single message.

One common solution is to insert a Code node between your compare datasets node and your Gmail node. In that Code node, you can loop through the items and build a single string that lists each animal and its value. For example:

JAVASCRIPTCopied
// Get all the items from the previous node
const items = $input.all();

// Build a string that contains each out-of-sync record
let messageBody = '';

for (const item of items) {
  // Adjust property names (like animal name and id) based on your actual data structure
  messageBody += `${item.json.animal}: ${item.json.id}\n`;
}

// Return the message so it can be referenced in the Gmail node
return [{ json: { message: messageBody } }];

Then in your Gmail node, you can reference the constructed message with an expression such as:

{{ $json.message }}

This approach aggregates the data from your compare datasets node into a single output which is then sent in one email.

Other methods include using an Aggregate node; however, the Code node often provides the flexibility needed for iterating over dynamic data and formatting the message exactly as you need it.

This solution makes it possible to send a single email with the boilerplate text and variable section listing the out-of-sync animals, rather than triggering an email for each individual item.