Table of Contents

Remove Unused Data Sources

  • 2026-01-09
  • Morten Lønskov

Overview

This best practice rule identifies data sources that are not referenced by any partitions or table expressions. Removing unused data sources reduces model complexity, improves maintainability, and prevents confusion.

  • Category: Maintenance
  • Severity: Low (1)

Applies To

  • Provider Data Sources
  • Structured Data Sources

Why This Matters

Unused data sources create unnecessary overhead:

  • Maintenance burden: Credentials and connection strings must be maintained for unused connections
  • Security concerns: Unnecessary connection strings may expose sensitive information
  • Model complexity: Extra objects clutter the data source list
  • Confusion: Developers may mistakenly use obsolete data sources
  • Deployment issues: Unused data sources may reference systems that no longer exist
  • Documentation overhead: Extra objects require explanation in model documentation

Unused data sources typically result from:

  • Refactoring partitions to use different sources
  • Consolidating multiple sources into one
  • Removing tables without cleaning up their data sources
  • Testing alternative connection methods

When This Rule Triggers

The rule triggers when a data source meets all these conditions:

UsedByPartitions.Count() == 0
and not Model.Tables.Any(SourceExpression.Contains(OuterIt.Name))
and not Model.AllPartitions.Any(Query.Contains(OuterIt.Name))

In other words:

  1. No partitions directly reference the data source
  2. No table source expressions (M queries) reference the data source by name
  3. No partition queries contain the data source name

How to Fix

Automatic Fix

This rule includes an automatic fix that deletes the unused data source:

Delete()

To apply:

  1. In the Best Practice Analyzer select flagged objects
  2. Click Apply Fix

Manual Fix

  1. In TOM Explorer, expand the Data Sources node
  2. Right-click the unused data source
  3. Select Delete
  4. Confirm the deletion

Before Deleting

Verify the data source is truly unused:

  • Check all partitions in all tables
  • Search M expressions for references to the data source name
  • Review custom expressions and calculated tables
  • Ensure no documentation references the connection

Example

Before Fix

Data Sources:
  - SQLServer_Production (Provider, used by Sales partition)
  - SQLServer_Staging (Provider, NOT USED)  ← Remove
  - AzureSQL_Archive (Structured, NOT USED)  ← Remove
  - PowerQuery_Web (Structured, used by Product partition)

After Fix

Data Sources:
  - SQLServer_Production (Provider, used by Sales partition)
  - PowerQuery_Web (Structured, used by Product partition)

Result: Simpler model with only necessary data sources

False Positives

The rule may flag data sources that are:

  • Referenced through dynamic M expressions using variables
  • Used in commented-out partition queries
  • Referenced by name in annotations or descriptions

Solution: Manually verify before deleting; add comments or annotations if the data source should be kept for documentation purposes.

Compatibility Level

This rule applies to models with compatibility level 1200 and higher.