Coding with AL – Overview

Why AL Is Object-Based

AL development is built entirely around objects, not free-floating code. Every piece of logic, data, or UI element must belong to a defined object type. This design enforces discipline, predictability, and upgrade safety.

Each AL object:

• Has a clear responsibility
• Participates in the ERP execution flow
• Interacts with other objects in controlled ways

Understanding object roles is essential before writing real-world AL solutions.

Core AL Object Categories

AL objects can be grouped into five core functional categories:

1. Data objects
2. User interface objects
3. Business logic objects
4. Output and processing objects
5. Extension and integration objects

Each category serves a distinct purpose.

Data Objects

Tables define how data is stored in Business Central. They represent structured ERP entities such as customers, items, documents, and ledger entries.

A table:

• Defines fields and data types
• Enforces primary keys
• Controls data integrity
• Serves as the foundation for all other objects

Tables do not contain UI logic. They represent business data, not screens.

Table extensions allow developers to add fields or logic to standard tables without modifying them.

They are used when:

• Additional data must be stored for standard entities
• Custom logic must react to standard table events

Table extensions are the primary mechanism for safe customization.

User Interface Objects

Pages define how users view and interact with data. They are the primary UI objects in Business Central.

Pages:

• Are always bound to a table or query
• Control layout, actions, and interaction
• Do not store data themselves

AL separates data storage (tables) from presentation (pages), which ensures consistency across the system.

Page extensions modify existing standard pages by:

• Adding fields
• Adding actions
• Hiding or rearranging UI elements

They allow UI customization without rewriting standard pages.

Business Logic Objects

Codeunits contain business logic and procedures. They are where calculations, validations, and automation live.

Codeunits:

• Do not store data
• Operate on records
• Are often triggered by events or actions

They act as service layers inside the ERP system.

Event subscribers allow custom logic to react to standard system events.

They are used to:

• Extend standard behavior
• Validate data
• Trigger automation
• Integrate with external systems

Event-driven design is central to upgrade-safe AL development.

Output and Processing Objects

Reports are used for:

• Document printing
• Batch processing
• Data aggregation

Reports can:

• Generate output (PDF, Excel)
• Perform background processing
• Combine data from multiple sources

They are not limited to printing.

Queries provide optimized data retrieval for:

• Reporting
• Integrations
• Performance-sensitive scenarios

They define how data is selected, not how it is stored or displayed.

Extension and Integration Objects

All AL objects live inside an extension. An extension is the deployment and versioning unit in Business Central.

Extensions:

• Package AL objects together
• Enable upgrade-safe deployments
• Support version control and lifecycle management

Developers never deploy individual objects—only extensions.

APIs expose Business Central data and logic to external systems.

They are used for:

• System integrations
• Data synchronization
• External applications

APIs are defined using AL objects but follow REST standards.

How AL Objects Work Together (Conceptual Flow)

A typical flow looks like this:

• Data is stored in tables
• Pages allow users to interact with that data
• Codeunits execute business logic
• Events trigger custom behavior
• Reports and queries process or expose data
• Extensions package everything safely

Each object plays a specific role. Misusing objects leads to unstable solutions.

Choosing the Right Object Type

One of the most important AL skills is choosing the correct object.

Examples:

• Storing data → Table
• Showing data → Page
• Calculating values → Codeunit
• Reacting to system behavior → Event Subscriber
• Printing or batch work → Report

Correct object choice keeps solutions clean and maintainable.

Summary

AL objects define the structure, behavior, and presentation of Business Central extensions. Understanding the role of each object type is essential before writing real-world AL code.

Once this object-level understanding is clear, learning syntax and advanced techniques becomes significantly easier.