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add diagram to errors page

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Deborah Barnard
2024-02-13 12:53:53 +00:00
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docs/data/data-mapping/data-item-linking/item-linking-errors.md
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@@ -50,6 +50,11 @@ Refer to [Item linking concepts](/data/data-mapping/data-item-linking/item-linki
When using expressions, you can reference data from any previous node. This doesn't have to be the node just before: it can be any previous node in the chain. When referencing nodes further back, you use the expression syntax `$(node_name).item`. Refer to [Mapping in expressions](/data/data-mapping/data-mapping-expressions/) for more information on using this expression.
<figure markdown>
![A diagram showing the threads linking multiple items back through a workflow](/_images/data/data-mapping/data-item-linking/item-linking-multiple-lines.png)
<figcaption markdown>Diagram of threads for different items. Due to the item linking, you can get the actor for each movie using `$('Get famous movie actors).item`.</figcaption>
</figure>
Since the previous node can have multiple items in it, n8n needs to know which one to use. When using `.item`, n8n figures this out for you behind the scenes. Refer to [Item linking concepts](/data/data-mapping/data-item-linking/item-linking-concepts/) for detailed information on how this works.
`.item` fails if information is missing. To figure out which item to use, n8n maintains a thread back through the workflow's nodes for each item. For a given item, this thread tells n8n which items in previous nodes generated it. To find the matching item in a given previous node, n8n follows this thread back until it reaches the node in question.