AL Method Attributes

What Are Method Attributes in AL?

Method attributes are metadata instructions applied to procedures. They are written in square brackets ([ ]) and placed directly above a procedure definition.

They do not change the internal logic of the procedure. Instead, they tell the Business Central runtime how that procedure should be treated.

In simple terms:

• Logic = what the procedure does
• Attribute = how the platform allows it to behave

Why Method Attributes Exist in Business Central

Business Central is:

• Cloud-first
• Multi-tenant
• Extension-based
• Continuously upgraded

In such an environment, unrestricted method access would be dangerous. Method attributes exist to enforce:

• Encapsulation
• Extension isolation
• Safe integrations
• Backward compatibility
• Predictable execution

They are a core part of Business Central’s upgrade-safe design philosophy.

Classification of Method Attributes

For practical understanding, method attributes can be grouped into five categories:

1. Visibility and access control
2. Extension-to-extension communication
3. Integration and service exposure
4. Event handling
5. Runtime behavior and lifecycle control

Each category is explained in detail below.

These attributes control who can call a method and from where.

The Internal attribute restricts a method so it can be called only from within the same extension.

[Internal]
procedure CalculateInternalMargin(): Decimal
begin
    exit(500.00);
end;
    

Without Internal, methods can accidentally become accessible across extensions, creating hidden dependencies.

• Helper methods
• Shared logic within the same app
• Core calculations that must not be reused externally

Best practice

Most reusable logic inside an extension should be Internal by default.

A local procedure is only accessible within the same object.

local procedure ValidateLine()
begin
end;
    

This is the strongest form of encapsulation.

• Logic is object-specific
• Reuse is not required

Restricts a method to on-premises environments only.

[Scope('OnPrem')]
procedure ReadLocalFile()
begin
    // File system access
end;
    

Cloud environments do not allow local file system or OS-level access.

• File handling
• Local hardware integration
• Legacy systems

This attribute prevents cloud publishing errors.

These attributes control how other extensions interact with your logic.

The External attribute exposes a method to other extensions.

[External]
procedure CalculateCommission(Amount: Decimal): Decimal
begin
    exit(Amount * 0.05);
end;
    

Some extensions act as shared libraries or frameworks.

• Providing reusable logic intentionally
• Building shared utilities
• Designing app ecosystems

Overuse causes:

• Tight coupling
• Breaking changes
• Difficult upgrades

Only expose what you are prepared to support long-term.

• Internal → reusable inside the extension
• External → reusable by others (public API)

If unsure, choose Internal.

These attributes expose AL methods outside Business Central.

The ServiceEnabled attribute exposes a method as a web service endpoint.

[ServiceEnabled]
procedure CreateCustomer(CustomerNo: Code[20]; Name: Text[100])
begin
    // Customer creation logic
end;
    

ERP systems must integrate with:

• Web portals
• Mobile apps
• Middleware
• External systems

• Methods must be stateless
• Input validation is mandatory
• Security permissions must be enforced

• Creating APIs
• Triggering ERP logic externally

• For internal logic
• For UI-dependent behavior

• ServiceEnabled → method-based services
• API Pages → data-centric REST APIs

Choose based on integration design.

These attributes are the foundation of upgrade-safe extensions.

The EventSubscriber attribute allows a method to react to system or application events.

[EventSubscriber(ObjectType::Table, Database::Customer, 'OnAfterInsertEvent', '', false, false)]
local procedure OnCustomerInserted(var Rec: Record Customer)
begin
    Message('Customer %1 created.', Rec."No.");
end;
    

Direct modification of standard code is not allowed.

• Method is never called directly
• Triggered by platform events
• Multiple subscribers allowed

• Extending standard behavior
• Adding validations
• Triggering automation

Event subscribers are the preferred extension mechanism in AL.

These attributes control how methods behave during execution and over time.

The TryFunction attribute allows a method to fail without throwing a runtime error.

[TryFunction]
procedure TryPostInvoice()
begin
    Error('Posting failed');
end;
    

• Errors are suppressed
• Caller checks success or failure

if TryPostInvoice() then
    Message('Success')
else
    Message('Failed');
    

• Batch processing
• Background jobs
• Integrations
• Retry logic

• To hide bad logic
• To bypass validations

Marks a method as deprecated.

[Obsolete('Use CalculateNewDiscount instead', '23.0')]
procedure CalculateOldDiscount()
begin
end;
    

Extensions evolve. Removing methods immediately breaks dependent code.

• Shows compiler warnings
• Guides developers to new logic
• Preserves backward compatibility

This is essential for long-lived extensions.

Controls severity:

• Pending
• Removed

Used in advanced versioning strategies.

Method attributes force developers to think in terms of:

• API boundaries
• Encapsulation
• Upgrade safety
• Responsibility separation

Well-designed extensions:

• Expose very few External methods
• Prefer Internal + events
• Use ServiceEnabled sparingly
• Deprecate instead of deleting

Common Developer Mistakes

• Marking everything as External
• Using ServiceEnabled without security
• Using TryFunction to mask errors
• Forgetting to deprecate old methods
• Ignoring scope differences

These mistakes lead to fragile extensions.

Summary

Method attributes in AL define how procedures are exposed, restricted, executed, and maintained. They are a cornerstone of Business Central’s extension architecture.

Understanding method attributes allows developers to:

• Build upgrade-safe solutions
• Control integration boundaries
• Avoid tight coupling
• Maintain extensions over multiple versions

Mastery of method attributes separates basic AL coders from professional Business Central developers.