Table Extensions

Extend standard Business Central tables with custom fields using table extensions.

30 minIntermediate

Learning Objectives

Create table extensions for standard BC tables
Add custom fields to Customer, Item, and Sales tables
Understand field ID ranges in extensions
Use extension events on standard tables

Why Table Extensions?

You cannot modify Microsoft's base tables directly. Table extensions let you add fields, keys, and triggers to existing tables without touching the base application.

This is the primary customization pattern for per-tenant and AppSource extensions.

Creating a Table Extension

CustomerExt.TableExt.al

tableextension 50100 CustomerExt extends Customer
{
    fields
    {
        field(50100; "Loyalty Points"; Integer)
        {
            Caption = 'Loyalty Points';
            DataClassification = CustomerContent;
            Editable = false;
        }
        field(50101; "Loyalty Tier"; Enum "Loyalty Tier")
        {
            Caption = 'Loyalty Tier';
            DataClassification = CustomerContent;
        }
        field(50102; "Last Bonus Date"; Date)
        {
            Caption = 'Last Bonus Date';
            DataClassification = CustomerContent;
        }
    }

    keys
    {
        key(Loyalty; "Loyalty Tier", "Loyalty Points")
        {
        }
    }
}

Field Numbering

Extension fields must use IDs from your allocated idRanges in app.json. Never use field IDs from the base application range.

Extending Multiple Tables

Common tables developers extend:

SalesHeaderExt.TableExt.al

tableextension 50101 SalesHeaderExt extends "Sales Header"
{
    fields
    {
        field(50100; "Approval Status"; Enum "Approval Status")
        {
            Caption = 'Approval Status';
            DataClassification = CustomerContent;
        }
        field(50101; "Approved By"; Code[50])
        {
            Caption = 'Approved By';
            DataClassification = EndUserIdentifiableInformation;
            Editable = false;
        }
    }
}

Extension Triggers

You can add triggers to extended tables:

tableextension 50102 ItemExt extends Item
{
    fields
    {
        field(50100; "Warranty Months"; Integer)
        {
            Caption = 'Warranty Months';
            DataClassification = CustomerContent;

            trigger OnValidate()
            begin
                if "Warranty Months" < 0 then
                    Error('Warranty months cannot be negative.');
            end;
        }
    }

    trigger OnBeforeInsert()
    begin
        if "Warranty Months" = 0 then
            "Warranty Months" := 12; // Default 12 months
    end;
}

Page Extensions for New Fields

Fields added via table extensions need corresponding page extensions to appear in the UI:

CustomerCardExt.PageExt.al

pageextension 50100 CustomerCardExt extends "Customer Card"
{
    layout
    {
        addafter("Credit Limit (LCY)")
        {
            field("Loyalty Points"; Rec."Loyalty Points")
            {
                ApplicationArea = All;
                ToolTip = 'Specifies the customer loyalty points balance.';
            }
            field("Loyalty Tier"; Rec."Loyalty Tier")
            {
                ApplicationArea = All;
            }
        }
    }
}

Tip

Always create page extensions alongside table extensions. Fields invisible to users provide no business value.

Best Practices

Group related fields — Use consistent field number ranges per feature
Document with ToolTip — Every field needs a ToolTip on its page extension
Plan ID ranges — Reserve ranges per module in app.json
Test upgrades — Extensions must survive BC version upgrades

Next Steps

Learn about FlowFields and CalcFields — powerful computed field patterns unique to BC/NAV.