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bcquality/custom/knowledge/patterns/cmfrt-interface-injection.md
BeytullahCengiz88 c72c0ad685 Add CMFRT coding standards documentation and examples 
- Introduced guidelines for "one codeunit one global function" architecture to enforce single responsibility in AL code.
- Added best practices and anti-patterns for adding parameters via overloads to maintain backward compatibility.
- Documented the importance of never deleting members in AL and always marking them as obsolete.
- Established the requirement for OnBefore and OnAfter integration events for global procedures to enhance extensibility.
- Defined naming conventions for CMFRT objects, including prefixes and object ID ranges to avoid conflicts.
- Implemented patterns for case statements to ensure all cases are handled, including the necessity of an else clause.
- Introduced the interface injection pattern to allow pluggable operations in table-level code.
- Recommended using Confirm Management for user confirmations to improve testability.
- Established a three-permission set pattern for security to ensure proper access control.
- Created a review skill for CMFRT AL standards to automate compliance checks against established guidelines.
2026-07-02 13:12:09 +00:00

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CMFRT interface injection pattern

Description

The CMFRT interface injection pattern makes any table-level operation pluggable by dependent extensions using a four-step structure. Step 1: define an AL interface with a single procedure matching the operation's signature. Step 2: add a parameterless entry-point procedure on the base table that instantiates the default implementation codeunit, fires an OnBefore integration event with var Handled: Boolean, exits early if Handled is true, and otherwise calls the overloaded form in Step 3. Step 3: add an overloaded procedure on the same table that accepts the interface as a parameter and delegates to it. Step 4: declare the [IntegrationEvent(false, false)] OnBefore event as a local procedure passing var Handled: Boolean. Dependent extensions subscribe to OnBefore, set Handled := true, and call the overloaded procedure with their own implementation codeunit.

Best Practice

Apply this pattern whenever a calculation or operation might need different behaviour in different customer deployments. The separation between the parameterless entry-point and the interface-accepting overload means a subscriber can inject an alternative implementation without modifying the base table. The default implementation remains the fallback for all extensions that do not subscribe.

See sample: cmfrt-interface-injection.good.al.

Anti Pattern

Placing the entire implementation directly inside the entry-point procedure with no interface and no OnBefore event. Monolithic entry points cannot be overridden by a subscriber without an AL override pattern, which is a breaking change for the overriding extension every time the base procedure is updated.

See sample: cmfrt-interface-injection.bad.al.