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- 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.
26 lines
1.9 KiB
Markdown
26 lines
1.9 KiB
Markdown
---
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bc-version: [all]
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domain: patterns
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keywords: [interface, injection, extensibility, implementation, handled, on-before, pluggable, override]
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technologies: [al]
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countries: [w1]
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application-area: [all]
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---
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# CMFRT interface injection pattern
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## Description
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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.
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## Best Practice
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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.
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See sample: `cmfrt-interface-injection.good.al`.
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## Anti Pattern
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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.
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See sample: `cmfrt-interface-injection.bad.al`.
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