Business Central Custom API – Episode 1: Laying the Foundation Before You Code

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Sohail Ahmed

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Introduction:

Custom APIs in Business Central are powerful tools that allow you to securely expose data, interact with external systems, and automate processes.
However, a surprising number of API projects run into trouble — and the issue isn’t usually the AL code. The real problem often lies in how little planning was done before the first line was written.

In this first episode of our Beginner-to-Advanced Custom API Series, we’ll go beyond the basics and give you practical steps, examples, and pro tips that will set you up for successful API development in Business Central.

Define the Data Flow:

Before you even think about page objects or endpoints, ask yourself:

What business process am I supporting?
Where is the data coming from? (Table, query, calculated value)
Where will it go? (External system, data warehouse, another BC company)
What triggers it? (User action, schedule, event)

Example:

If you’re creating a Custom API to share item availability with an e-commerce site, your data source might be the Item and Item Ledger Entry tables. Your destination might be a Shopify API endpoint. The trigger could be either:

On-demand (user clicks “Sync Inventory”)
Real-time (whenever availability changes)

Review Standard APIs First:

Business Central comes with a robust library of standard APIs that Microsoft maintains.

Before you create something from scratch, always check if a standard API can serve your needs.

Saves development time
Reduces maintenance overhead
Ensures compatibility with Microsoft’s roadmap

Example:
If you need to expose customer data, the Customer API might already give you 80% of what you need. You can extend it rather than starting over.

Reference Link:

https://github.com/microsoft/ALAppExtensions/blob/main/Apps/W1/APIV2/app/src/pages/APIV2ItemLedgerEntries.Page.al

Respect Business Logic:

One of the most common mistakes in Custom API development is bypassing core BC logic.

Posting routines, validations, and workflows exist to protect data integrity and compliance. Skipping them can cause:

Data inconsistencies
Broken processes
Invalid financial entries

Example:

If your API is designed to post sales orders, don’t insert directly into Sales Header and Sales Line tables — call the posting routines so that validations and ledger updates happen automatically.

Pro Tip: Think of BC’s business logic as guardrails. Working within them ensures your API won’t create downstream problems.

Plan for Timing & Usage

APIs can be used in different ways — and your design choices will vary accordingly:

Real-time ⚡ – Ideal for instant data syncs like payment processing or live inventory.
Scheduled ⏰ – Great for bulk data transfers at off-peak times.
Event-driven 🔔 – Automatically triggered by a change in BC, perfect for notifications or updates.

Example:

If your external system can’t handle large bursts of requests, a scheduled sync at midnight might be better than a real-time push.

Pro Insight

A great Custom API in Business Central feels like it’s part of the product itself — not a hack bolted on the side.

What’s Next in the Series

Over the coming episodes, we’ll cover everything from creating your first API page object to advanced techniques like:

Securing endpoints with OAuth 2.0
Handling nested entities and complex data shapes
Optimizing performance for high-volume requests
Integrating with external systems using best practices

Next Episode Preview:

In Episode 2, we’ll create our first Custom API in Business Central and learn how to consume it through Postman. This will give you a practical, hands-on start to API development.

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