Forum Discussion
Fabric having issues importing or ingesting json files and responses
Hi smeetsh , Yeah, I think the issue is with the JSON complexity rather than the payload size too. Fabric generally handles large JSON files fine, but deeply nested and irregular schemas with optional arrays/objects can make the automatic schema import struggle or hang. The fact that even the smaller endpoint failed during schema import points more toward a schema inference limitation than a pure performance problem.
Your notebook -> Lakehouse -> ETL/Warehouse approach is probably the better fit here anyway. Spark gives you much more control over flattening arrays, handling nullable branches and managing evolving schemas compared to relying on automatic inference in the import UI.
Hi smeetsh , Thank you for reaching out to the Microsoft Community Forum.
This sounds more like a Fabric/Dataflow schema inference issue than a problem with the actual file size. A 3 MB JSON is not especially large and the fact that even the smaller 50 KB response hangs points more toward the parser struggling with the nested structure and arrays during automatic schema detection.
I do not think Microsoft intentionally changed support for nested JSON, but I did hear about of flaky behaviour around complex JSON imports and schema detection in Fabric. The generic “Failed to import source schema. undefined” error is usually thrown before the actual transformations even start, so the failure is likely happening during the import/inference step itself.
As a workaround, you can ingest the raw JSON first and then expand it manually step by step in Power Query, instead of relying on automatic schema import. If possible, testing with a simplified or partially flattened response can also help confirm whether a specific nested branch is causing the parser to choke.