Table of Contents

Use Compound Names for User-Defined Functions

  • 2026-03-19
  • Morten Lønskov

Overview

This best practice rule identifies User-Defined Functions (UDFs) whose names do not contain a separator character (. or _). Compound names prevent naming conflicts if Microsoft introduces a built-in DAX function with the same name.

  • Category: Error Prevention

  • Severity: Low (1)

Applies To

  • User-Defined Functions

Why This Matters

UDFs without separator characters in their names risk breaking in the future:

  • Naming conflicts: If Microsoft adds a new built-in DAX function with the same name as your UDF, the built-in function takes precedence and your UDF will stop working
  • Ambiguity: Without a namespace or prefix, it is unclear whether a function call refers to a built-in DAX function or a custom UDF
  • Maintenance burden: Renaming UDFs after a conflict occurs requires updating all references throughout the model

Using compound names (e.g., Finance.CalcProfit or My_CalcProfit) makes your UDFs distinguishable from built-in DAX functions.

When This Rule Triggers

The rule triggers when a UDF name contains neither a period nor an underscore:

not Name.Contains(".") and not Name.Contains("_")

How to Fix

Manual Fix

  1. In the TOM Explorer, locate the User-Defined Function
  2. Rename it to include a namespace separator (.) or underscore (_)
  3. Tabular Editor automatically updates all references throughout the model

Common Causes

Cause 1: Simple Naming

The function was given a plain name without considering future conflicts.

Cause 2: Imported from Query

A UDF was applied from a DAX query DEFINE section where namespace conventions were not followed.

Example

Before Fix

// Function named without separator
FUNCTION CalcProfit =
    (
        revenue: DOUBLE,
        cost: DOUBLE
    )
    => revenue - cost

After Fix

// Function named with namespace separator
FUNCTION Finance.CalcProfit =
    (
        revenue: DOUBLE,
        cost: DOUBLE
    )
    => revenue - cost

Compatibility Level

This rule applies to models with compatibility level 1702 and higher.