Support User-Defined Data Types (UDTs) in SQL Server Mirroring for Microsoft Fabric

[jasonhorner]

Description

Currently, SQL Server mirroring in Microsoft Fabric does not support User-Defined Data Types (UDTs). This limitation blocks ingestion and mirroring scenarios for databases that rely on UDTs, even when those UDTs are simple aliases of fully supported native SQL Server data types.

Business Impact

We are working with a third-party vendor database where:

• The schema is not under our control
• UDTs are used extensively throughout the model
• These UDTs are aliases of standard SQL Server data types (e.g., VARCHAR, INT, etc.)

Because of this limitation, we are unable to leverage Fabric mirroring for this data source without introducing complex and potentially fragile workarounds (e.g., schema replication, type conversion layers, or ETL pipelines).

Rationale

Under the hood, SQL Server alias UDTs map directly to base system types. From a data movement and storage perspective, these should be fully compatible with existing Fabric mirroring capabilities.

Blocking on UDTs:

• Creates unnecessary friction for onboarding common enterprise systems
• Prevents adoption in scenarios involving vendor-managed schemas

Requested Enhancement

Enable support for User-Defined Data Types (UDTs) in SQL Server mirroring by:

• Automatically resolving alias UDTs to their underlying base data types during ingestion/mirroring
  or
• Providing a configuration option to map UDTs to their base types

Expected Outcome

• Seamless mirroring of SQL Server databases that use alias UDTs
• Elimination of unnecessary preprocessing or schema transformation steps
• Broader adoption of Fabric mirroring in enterprise environments with vendor-controlled schemas

Additional Notes

This request specifically targets alias UDTs, not complex CLR-based types.