Introduction

In Microsoft Dynamics 365 Business Central, a Codeunit is an AL object designed to store reusable business logic and process automation.

Codeunits are essential for:

• Posting routines
• Batch processing
• Scheduled automation
• API integrations
• Workflow execution
• Validation services

Unlike tables, codeunits focus on process execution rather than data storage.

What is a Codeunit?

A Codeunit acts as a processing engine where developers centralize logic for:

• Customer processing
• Sales posting
• Purchase workflows
• Financial transactions
• Notifications
• Integration logic

Benefits:

• Reusable logic
• Modular design
• Better maintenance
• Scalable architecture

Main Codeunit Triggers

1. OnRun()

Overview

OnRun() is the primary execution trigger of a codeunit.

Whenever the codeunit is executed, this trigger runs automatically.

Syntax:

trigger OnRun()
begin
    Message('Codeunit started');
end;

Example:

codeunit 50100 "Customer Processor"
{
    trigger OnRun()
    begin
        Message('Processing customer records...');
    end;
}

Common Uses:

• Batch posting
• Data processing
• Automation jobs
• Workflow management
• Scheduled reports

2. OnCheckPreconditions()

Overview

This trigger runs before OnRun() to verify whether setup and conditions are valid.

Syntax:

trigger OnCheckPreconditions()
begin
    if SetupMissing then
        Error('Setup required');
end;

Example:

trigger OnCheckPreconditions()
begin
    if not SalesSetup.Get() then
        Error('Sales setup must be completed first.');
end;

Common Uses:

• Setup validation
• Permission checks
• Configuration verification
• Security controls
• Mandatory checks

Best Practices for Codeunits

Keep Logic Modular

Separate code into:

• Validation procedures
• Posting procedures
• Utility functions
• Integration services

Avoid Heavy UI Logic

Codeunits often run in:

• Background jobs
• APIs
• Job queues

Always Validate Before Execution

Use:

• Error()
• TestField()
• Preconditions

Common Business Scenarios

Goal	Trigger
Main process execution	OnRun
Validate setup	OnCheckPreconditions
Batch automation	OnRun
Security checks	OnCheckPreconditions

Beginner Mistakes to Avoid

• Writing all logic in one codeunit
• Skipping validations
• Poor modularity
• Overusing messages
• Missing security checks

Conclusion

Codeunit triggers are the foundation of reusable business process automation in Business Central.

By mastering:

• OnRun()
• OnCheckPreconditions()

Developers can build:

• Reliable workflows
• Scalable ERP processes
• Secure business logic
• Professional AL solutions

Strong Codeunit design ensures efficient Business Central customization.