Forum Discussion
Copy activity dynamically populated additional columns error when using Expression values
Hi patto_uon ,
Thanks for the clarification. To confirm, expressions such as @{formatDateTime(utcNow())} are only evaluated when they are authored directly inside the pipeline. When the same string comes from external metadata, Fabric treats it as normal text, which is why you see the expression printed instead of the evaluated value.
So when I mentioned a “pipeline-ready expression format,” it meant that your metadata should contain the information needed to build a valid expression, but the pipeline still needs to convert that metadata into an actual expression before passing it to the Copy activity. Currently, the service cannot execute expressions coming directly from metadata files.
To achieve a metadata-driven approach, a small preprocessing step in the pipeline is required to translate metadata into real expressions.
Thank you.
Hi patto_uon ,
Thank you for reaching out to the Microsoft fabric community forum.
Could you please let us know if the issue has been resolved? I wanted to check if you had the opportunity to review the information provided by nielsvdc . If you still require support, please let us know, we are happy to assist you.
Thank you.
Hey Anonymous, no unfortunately I still have the same issue.
- If I load metadata from a file that contains the "type": "Expression" terminology into a variable and then pass that into the copy activity, then I receive the original error message ("Failed to convert the value in 'value' property to 'System.String' type")
- If I write the expression directly into the set variable activity, it all works. However, that doesn't allow my engineers to write expressions in their metadata.