/skill-api

name: skill-api
description: "AL API development patterns for Business Central. Use when creating OData/REST API pages, HttpClient integrations, webhook implementations, or any external system integration via API."

Skill: AL API Development

Purpose

Design and implement RESTful API pages for Business Central: API page v2.0 patterns, OData conventions, versioning, bound/unbound actions, webhooks, header-lines navigation, and performance-optimized endpoints.

When to Load

This skill should be loaded when:

• A new API page (PageType = API) needs to be designed or implemented
• Existing BC data must be exposed to external consumers (Power Platform, mobile apps, 3rd-party)
• Custom bound or unbound actions are needed on API endpoints
• An API versioning strategy or deprecation plan is required
• Webhook subscriptions need to be configured for change notifications
• API performance or filtering needs optimization

Core Patterns

Pattern 1: API Page v2.0 (Standard CRUD Endpoint)

page 50100 "Contoso Sales Orders API"
{
    APIVersion = 'v2.0';
    APIPublisher = 'contoso';
    APIGroup = 'sales';

    EntityCaption = 'Sales Order';
    EntitySetCaption = 'Sales Orders';
    EntityName = 'salesOrder';               // singular — used in URL for single entity
    EntitySetName = 'salesOrders';           // plural — used in URL for collection

    PageType = API;
    SourceTable = "Sales Header";
    SourceTableView = where("Document Type" = const(Order));
    DelayedInsert = true;                    // required — defers insert until all fields set
    ODataKeyFields = SystemId;               // required — use SystemId for stable GUIDs

    layout
    {
        area(Content)
        {
            repeater(Group)
            {
                field(id; Rec.SystemId)
                {
                    Caption = 'Id';
                    Editable = false;
                }
                field(number; Rec."No.")
                {
                    Caption = 'Number';
                    Editable = false;
                }
                field(orderDate; Rec."Order Date")
                {
                    Caption = 'Order Date';
                }
                field(customerNumber; Rec."Sell-to Customer No.")
                {
                    Caption = 'Customer Number';
                }
                field(customerName; Rec."Sell-to Customer Name")
                {
                    Caption = 'Customer Name';
                    Editable = false;
                }
                field(totalAmountIncludingVAT; Rec."Amount Including VAT")
                {
                    Caption = 'Total Amount Including VAT';
                    Editable = false;
                }
                field(status; Rec.Status)
                {
                    Caption = 'Status';
                    Editable = false;
                }
                field(lastModifiedDateTime; Rec.SystemModifiedAt)
                {
                    Caption = 'Last Modified Date Time';
                    Editable = false;
                }
            }
        }
    }
}

**Resulting endpoint:**

GET  /api/contoso/sales/v2.0/companies({companyId})/salesOrders
GET  /api/contoso/sales/v2.0/companies({companyId})/salesOrders({id})
POST /api/contoso/sales/v2.0/companies({companyId})/salesOrders
PATCH /api/contoso/sales/v2.0/companies({companyId})/salesOrders({id})
DELETE /api/contoso/sales/v2.0/companies({companyId})/salesOrders({id})

**Property rules:**

• `ODataKeyFields = SystemId` — always use `SystemId` for stable, immutable keys
• `DelayedInsert = true` — mandatory on API pages (lets BC set defaults before committing)
• `SourceTableView` — pre-filter the source if the table serves multiple document types
• Field names use **camelCase** (OData convention): `customerNumber`, not `Customer_Number`
• `Editable = false` on computed/system fields to prevent consumer confusion

Pattern 2: Header-Lines with Navigation Property

Expose parent-child relationships via `part` subpages:

// Add inside the header API page's repeater:
part(salesOrderLines; "Contoso Sales Order Lines API")
{
    Caption = 'Lines';
    EntityName = 'salesOrderLine';
    EntitySetName = 'salesOrderLines';
    SubPageLink = "Document Type" = field("Document Type"),
                  "Document No." = field("No.");
}

// Lines API page (subpage)
page 50101 "Contoso Sales Order Lines API"
{
    APIVersion = 'v2.0';
    APIPublisher = 'contoso';
    APIGroup = 'sales';

    EntityCaption = 'Sales Order Line';
    EntitySetCaption = 'Sales Order Lines';
    EntityName = 'salesOrderLine';
    EntitySetName = 'salesOrderLines';

    PageType = API;
    SourceTable = "Sales Line";
    DelayedInsert = true;
    ODataKeyFields = SystemId;

    layout
    {
        area(Content)
        {
            repeater(Group)
            {
                field(id; Rec.SystemId) { Editable = false; }
                field(lineNumber; Rec."Line No.") { Editable = false; }
                field(lineType; Rec.Type) { Caption = 'Type'; }
                field(itemNumber; Rec."No.") { Caption = 'Item Number'; }
                field(description; Rec.Description) { Caption = 'Description'; }
                field(quantity; Rec.Quantity) { Caption = 'Quantity'; }
                field(unitPrice; Rec."Unit Price") { Caption = 'Unit Price'; }
                field(lineAmount; Rec."Line Amount") { Caption = 'Line Amount'; Editable = false; }
            }
        }
    }
}

**Consumer usage:**

# Get order with lines expanded
GET /salesOrders({id})?$expand=salesOrderLines

# Get lines for a specific order
GET /salesOrders({id})/salesOrderLines

# Add a line to an order
POST /salesOrders({id})/salesOrderLines
{ "lineType": "Item", "itemNumber": "ITEM-001", "quantity": 10 }

Pattern 3: Bound Actions (Operate on Entity)

Bound actions trigger business logic on a specific entity:

//