How to Append Data to a CSV File in Fabric Copy Data Activity?

Hello bhavya5903 

NandanHegde  is absolutely right. Here are more details 

appending data directly to an existing CSV file using the Copy Data activity in Microsoft Fabric is not natively supported. The Copy Data activity in Fabric is designed to write to a destination in either overwrite or create mode, but it does not support appending data to an existing file directly.

Why Appending Is Not Supported

The Copy Data activity overwrites the file in the sink by default because it treats each execution as a new write operation. CSV files are not structured like databases, so they lack native support for incremental updates or appends within the same file.

Workarounds to Achieve Appending

If you need to append data to a CSV file, you can use one of the following approaches:
1. Use a Staging File and Merge
• Write each iteration of data into separate files (e.g., `file1.csv`, `file2.csv`).
• At the end of the loop or pipeline execution, use a script or another process (e.g., a notebook or Dataflow) to merge all these files into a single CSV file.

better approach would be to in Dataflow Gen2, ingest JSON by parsing or flattening it, then configure the Delta table as the destination with “Append” mode.

hope this helps 

if this is helpful please accept the answer and give kudos

Files can be merged using Copy activity as well:

https://www.sqlservercentral.com/articles/merge-multiple-files-in-azure-data-factory

no need of Dataflow Gen 2 or custom code specifically