Exam MB-500 topic 4 question 5 discussion

Actual exam question from Microsoft's MB-500

Question #: 5
Topic #: 4

HOTSPOT -
You have a Dynamics 365 Finance environment.
You have the following code: (Line numbers are included for reference only.)

For each of the following statements, select Yes if the statement is true. Otherwise, select No.
NOTE: Each correct selection is worth one point.
Hot Area:

Show Suggested Answer

Suggested Answer:

Box 1: Yes -
Class extension - Method wrapping and Chain of Command.
The functionality for class extension, or class augmentation, has been improved. You can now wrap logic around methods that are defined in the base class that you're augmenting. You can extend the logic of public and protected methods without having to use event handlers. When you wrap a method, you can also access public and protected methods, and variables of the base class. In this way, you can start transactions and easily manage state variables that are associated with your class.

Box 2: Yes -
In the following example, the wrapper around doSomething and the required use of the next keyword create a Chain of Command (CoC) for the method. CoC is a design pattern where a request is handled by a series of receivers. The pattern supports loose coupling of the sender and the receivers
[ExtensionOf(classStr(BusinessLogic1))]
final class BusinessLogic1_Extension
{
str doSomething(int arg)
{
// Part 1
var s = next doSomething(arg + 4);
// Part 2
return s;
}
}

Box 3: Yes -
Instance and static methods can be wrapped by extension classes. If a static method is the target that will be wrapped, the method in the extension must be qualified by using the static keyword.

Box 4: No -
Wrapper methods must always call next.
Note: Wrapper methods in an extension class must always call next, so that the next method in the chain and, finally, the original implementation are always called. This restriction helps guarantee that every method in the chain contributes to the result.
In the current implementation of this restriction, the call to next must be in the first-level statements in the method body.
Here are some important rules:
✑ Calls to next can't be done conditionally inside an if statement.
✑ Calls to next can't be done in while, do-while, or for loop statements.
✑ A next statement can't be preceded by a return statement.
✑ Because logical expressions are optimized, calls to next can't occur in logical expressions. At runtime, the execution of the complete expression isn't guaranteed.
Reference:
https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/extensibility/method-wrapping-coc

by BigFritz at Dec. 9, 2020, 7:59 p.m.

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Einestien

Highly Voted 4 years, 2 months ago

The answer of the question is correct Yes,Yes,Yes and No

upvoted 25 times

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globeearth

Most Recent 1 month ago

The given answer is correct. The 4th requirement - No. The reason is given below: --> An extension class is essentially a static augmentation of the base class. It does not exist as a standalone class that you can instantiate directly. Instead, it extends the behavior of the base class, and its methods are "merged" into the base class at runtime. --> You cannot create an instance of the extension class itself in X++ when using the ExtensionOf attribute. Instead, instantiate the base class, and the system will incorporate the extension’s methods (both CoC-wrapped methods and new methods) automatically. This is by design to maintain the extensibility model

upvoted 1 times

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Aghenon

1 year ago

Yes, Yes, No, No Static methods cannot be wrapped or extended using the Chain of Command (CoC) pattern.

upvoted 1 times

Gince40

10 months, 2 weeks ago

Instance and static methods can be wrapped by extension classes. If a static method is the target that will be wrapped, the method in the extension must be qualified by using the static keyword.

upvoted 1 times

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Prollyx

3 years, 3 months ago

Yes - Yes - Yes - No

upvoted 2 times

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jovank

3 years, 4 months ago

New version of question asks about adding conditional logic on line 18. I suppose the answer is yes, although the question is weirdly formulated.. it doesn't say if the next call will be in the conditional logic.

upvoted 2 times

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Pir

4 years, 5 months ago

Last 4th option is Yes, on following link there are multiple example of class extension instantiation: https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/extensibility/class-extensions

upvoted 1 times

Bulhy

4 years, 5 months ago

I do not agree with you. On given link I haven't been able to find any mentioned code, that would instantiate a extension class. If you extend any class (talking in X++ logic here, which is via decorator [ExtensionOf]), the (original) extended class shall recognize any new methods and members, so why would you instantiate the extension class? You just instantiate the original/extended class and you get access to the new methods and members.. In your given link there are multiple code snippets, which support my explanation: 1. Look here at the second code snippet - https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/extensibility/class-extensions#instance-methods - they instantiate the original/extended MyClass "MyClass c = new MyClass();", they DO NOT instantiate the extension class (THIS IS WRONG) "MyClass_Extension = new MyClass_Extension();" 2. Same goes for this code snippet - https://docs.microsoft.com/en-us/dynamics365/fin-ops-core/dev-itpro/extensibility/class-extensions#instance-state So the 4th option is NO, iyam

upvoted 15 times

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