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Flow Builder Transform Element: ID Field Causes Validation Error When Selected as Join Key
Publish Date: May 22, 2026
Description
When configuring a Join transformation in the Transform element to combine two collections (e.g., Orders and Accounts) using fields such as Id -> AccountId as join keys, users may encounter the following errors if the field mapping is not properly completed:
- "No fields were selected to join. To select fields, edit the join transformation."
- "This join transformation has no mapped selected fields. Map selected fields to the target collection."
Resolution
The Transform element in Flow Builder supports joining two collections using an Inner Join. It requires three mandatory steps to be completed :
- Configure the join keys for each source collection
- Select the join fields to return into the target collection
- Map the fields from the joined source collections to the target collection
For detailed configuration steps, refer to these Help article: Join Collections in a Flow
Additional Resources
Knowledge Article Number
005385250
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