Drag and Drop Question You are a Dynamics 365 Finance developer for a company that sells pre-owned vehicles. When the company acquires a new vehicle, vehicle identification (VIN) numbers are added…

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Explanation

Explanation: D365 Finance VIN Validation Event Handler

Core Concept

In Dynamics 365 Finance, you never modify base objects directly. Instead, you use the event subscription model - copying event handler stubs and placing them in your own extension classes. The sequence reflects this pattern.

Why This Sequence

Step 1: Copy the validatedWrite event handler on the CustTable object

validatedWrite is the correct event because:

• It fires when a record is about to be saved to the database
• It returns a boolean - returning false blocks the save and displays an error to the user
• It is the standard D365F validation hook for table-level record validation

In the AOT, you right-click the validatedWrite method on CustTable and select "Copy event handler method" - this gives you a correctly-typed delegate stub you can subscribe to without touching the base object.

Why not the distractors:

• onWriting - fires during the write operation but is not designed to block saves with user-facing validation errors; it has no return value for validation
• onModified - fires when a field value changes in a form, not on save; this would fire on every keystroke, not at record commit

Step 2: Add the event handler method to a class

You paste the copied stub into a new X++ class (e.g., CustTableEventHandler). This class is your extension artifact - it owns the handler method and is where D365F's event subscription wiring points. You cannot register a free-floating function; it must live in a class.

Step 3: Add code to perform the validation

Only after the infrastructure exists (correct event, correct class) do you write the logic - checking strlen(custTable.VINField) >= 10, and calling checkFailed("VIN must be at least 10 characters") if it fails.

Common Mistakes

Summary

The sequence is event selection → infrastructure → logic - a pattern you'll repeat for any D365F event handler: pick the right hook, place it in an extension class, then implement the business rule.

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