Trying to Learn X++ for Dynamics 365? Don’t Waste Time — Master These Core Concepts First

If you’re diving into Microsoft Dynamics 365 Finance and Operations (D365FO) development, you’ve probably already heard the warning:

You’ll need to know X++.

But what no one tells you is that X++ isn’t just another language — it’s a weird hybrid that lives inside a massive ERP system and has its own way of thinking.

So instead of throwing yourself at a thousand-page manual or watching 8 hours of confusing tutorials, let’s cut straight to what actually matters.

First: What Even Is X++?

Think of X++ as:

• A C-style, object-oriented language
• Purpose-built for business logic inside Dynamics 365
• Living tightly inside the Dynamics application stack (DB, UI, and business layer all bundled)

It’s not a general-purpose language. It was made to get business things done — fast, but also in a specific way. So now let’s talk about the core concepts you actually need to get productive.

1. Tables Are Everything

In X++, tables are not just data storage. They’re mini-objects.

Each table:

• Has properties (like whether it’s a temp table or has an index)
• Can include methods (yes, code inside your table)
• May automatically map to forms or classes

You’ll write logic in them. You’ll build them into forms. You’ll extend them. Learn how initValue() or validateWrite() works inside tables. That alone will save you hours.

2. Classes and Objects

Yes, X++ supports OOP (object-oriented programming) — but it’s a little quirky.

Key things to master:

• RunBaseBatch and SysOperation for background jobs
• static vs. public methods (X++ loves static.)
• Passing references between objects and forms
• Knowing what classes are kernel vs. what’s user-defined

Start simple — build a class that takes input, runs a query, and shows an InfoLog.

3. The SELECT Statement Is Your Best Friend

You will write a lot of queries. X++ uses a SQL-like syntax, but don’t get too comfy — it has its own rules.

select firstOnly custTable
    where custTable.AccountNum == "1101";

You can even do joins, exists, and nested selects — but mistakes here can nuke performance. Avoid while select loops that hit the DB on every iteration. Learn how to buffer and batch properly.

4. Forms and FormDataSources = Real-World Headaches

Working on the UI side of D365? Get used to FormDataSources, FormControls, and handling user events.

These aren’t just UI widgets. You’ll often wire them to logic inside your tables or classes. Dig into FormDataSource.init() and FormDataSource.write() — that’s where the good stuff happens.

5. Events and Delegates

You don’t modify standard Microsoft code directly anymore.

Instead, you use

• Pre/post event handlers
• Chain of Command (CoC) extensions

Want to customize a field behavior without breaking the base app? Learn how to use preValidateWrite() in a CoC extension.

6. Exception Handling: You’re Gonna Need It

Yes, try-catch works in X++. But the error messages can be vague, and logging isn’t always helpful.

Learn how to:

• Use try { … } catch (Exception::Error) { … }
• Throw meaningful messages with error(), info(), or warning().
• Roll back database transactions the right way.

Wrap your DB transactions carefully — ttsBegin/ttsCommit aren’t optional.

7. Data Entities and Integration Magic

Need to move data in and out of D365? You’ll need data entities.

They’re:

• Abstractions over tables
• Auto-generated OData endpoints (with caveats)
• Mappable to Excel, APIs, and Power Platform

Don’t underestimate how powerful — and painful — it is to build custom entities.

8. Debugging: It’s a Whole Process

No, you can’t just “set a breakpoint and go.”

To debug X++:

• Attach Visual Studio to the AOS process.
• Use infolog() for inline sanity checks.
• Sometimes just restart everything.

Turn off your breakpoints when you’re done. Leaving them on can crash other devs.

9. Batch Jobs and Scheduling Logic

If your logic takes more than a second to run, you’ll probably move it into a batch.

Use:

• RunBaseBatch for legacy jobs
• SysOperation Framework for modern scheduling

Every serious project has batch logic. Learn how to make jobs that restart safely if they crash.

10. Security Roles and Permissions

Permissions aren’t just about UI access. You’ll run into:

• Security artifacts
• Privilege mapping
• Custom entry points in X++

Make sure any new forms, reports, or services are wired into the right roles — or your users will scream.

X++ isn’t the prettiest language. Once you understand its rhythm — the table-centric design, the tightly coupled UI logic, the ERP-first architecture — you’ll realize it’s actually… kind of brilliant.

So stop chasing shiny new frameworks for a second. If you want to build real business software with real impact, learning X++ well is your unfair advantage.