> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cognite.com/llms.txt
> Use this file to discover all available pages before exploring further.

# About Fabric OneLake in Transformations

> Learn how Transformations read Microsoft Fabric OneLake Delta tables without staging a full copy in CDF RAW.

<Warning>
  The features described in this article are in [public preview](/cdf/product_feature_status#public-preview) and may change.
</Warning>

[Transformations](/cdf/integration/concepts/transformation/index) can query Microsoft Fabric OneLake Lakehouse Delta tables without staging a full copy in CDF RAW. You register an **external data source**, then read it in SQL with `ext_onelake`. Transformation results are still written to CDF destinations such as data models.

Fabric remains the system of record for the source tables. Each run reads the current Delta table state over ABFSS (Azure Blob File System Secure).

## What this path does

| Aspect                | Behavior                                                                                                           |
| --------------------- | ------------------------------------------------------------------------------------------------------------------ |
| No RAW staging copy   | Jobs read Fabric Lakehouse tables at query time. Data is not bulk-loaded into CDF RAW only to enable the pipeline. |
| Query-time access     | Each run reads the current Delta table state.                                                                      |
| Credentials in CDF    | Connection metadata and secrets are stored encrypted in CDF.                                                       |
| Read-only from Fabric | Transformations do not write back to OneLake.                                                                      |
| Output in CDF         | Modeled results still land in CDF destinations.                                                                    |

## How it works

1. Register a Fabric OneLake integration as an **external data source** (credentials plus workspace and lakehouse IDs).
2. Reference a Delta table in transformation SQL with `ext_onelake(...)`.
3. Shape the data with Spark SQL.
4. Write the result to a CDF destination such as a data model.

You register the external data source with the Transformations API. Runtime stays in Transformations.

## Requirements

* Fabric Lakehouse **Delta** tables under `Tables/` (optional single schema folder).
* Microsoft Entra ID service principal with at least **Contributor** on the Fabric workspace or lakehouse (**Viewer** is not enough for OneLake API access).
* CDF capabilities for external data sources and Transformations.

## Next steps

<CardGroup cols={2}>
  <Card title="Set up an external data source" icon="gear" href="/cdf/integration/guides/transformation/set_up_fabric_onelake_connection">
    Register Fabric OneLake credentials and location with the API.
  </Card>

  <Card title="Read Fabric OneLake data" icon="code" href="/cdf/integration/guides/transformation/read_fabric_onelake">
    Query with `ext_onelake` and write to a CDF destination.
  </Card>
</CardGroup>

For API schemas, see [Transformation external data sources](/api-reference/concepts/20230101-beta/transformation-external-data) and the [beta OpenAPI tag](https://api-docs.cognite.com/20230101-beta/tag/Transformation-External-Data-Sources).