Table of Contents

Provide Format String for Numeric and Date Columns

  • 2026-01-09
  • Morten Lønskov

Overview

This best practice rule identifies visible columns with numeric or date data types that lack format strings. Format strings ensure consistent, professional data display across all client tools.

  • Category: Formatting

  • Severity: Medium (2)

Applies To

  • Data Columns
  • Calculated Columns
  • Calculated Table Columns

Why This Matters

Columns without format strings display inconsistently:

  • Unprofessional appearance: Raw numbers like 1234567.89 instead of $1,234,567.89
  • User confusion: Users can't tell if values are currency, percentages, or plain numbers
  • Inconsistent formatting: Different visuals may show different formats
  • Manual formatting burden: Users must format every visual individually
  • Date ambiguity: Dates show timestamps when only dates are needed

When This Rule Triggers

IsVisible
and string.IsNullOrWhitespace(FormatString)
and (DataType = "Int64" or DataType = "DateTime" or DataType = "Double" or DataType = "Decimal")

How to Fix

Manual Fix

  1. In TOM Explorer, select the column
  2. In Properties pane, locate the Format String field
  3. Choose from standard formats or enter custom format
  4. Save changes

Common Causes

Cause 1: Missing Format Definition

Columns do not have a format string when imported.

Example

Before Fix

Column: SalesAmount
Format String: (empty)

Display: 1234567.89 (hard to read, no currency symbol)

After Fix

Column: SalesAmount
Format String: "$#,0.00"

Display: $1,234,567.89 (clear, professional formatting)

Compatibility Level

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