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custom/knowledge/architecture/pages-must-not-contain-business-logic.md

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+---
+bc-version: [all]
+domain: architecture
+keywords: [page, trigger, onaction, modify, codeunit, logic]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+## Description
+
+In CURABIS codebases, pages are pure presentation. Business logic, calculations,
+validations, and record modifications belong in codeunits — not in page triggers
+or actions. This is stricter than the general BC guidance and applies to all
+CURABIS PTE apps.
+
+A page procedure that calculates a value and assigns it to a field, calls
+`Rec.Modify()` directly, or implements business rules is an architecture violation
+even if it compiles.
+
+**Exceptions:**
+- Setup pages may read and write their own setup record directly.
+- The designated "Run Conversion" page may call the conversion codeunit directly.
+
+## Anti Pattern
+
+```al
+// WRONG: calculation and Modify in a page action
+trigger OnAction()
+begin
+    Rec."Total Amount" := Rec.Quantity * Rec."Unit Price";
+    Rec."VAT Amount" := Rec."Total Amount" * 0.25;
+    Rec.Modify();
+end;
+```
+
+```al
+// WRONG: validation logic in page trigger
+trigger OnValidate()
+begin
+    if Rec.Quantity < 0 then
+        Error('Quantity cannot be negative');
+    Rec."Total Amount" := Rec.Quantity * Rec."Unit Price";
+end;
+```
+
+## Best Practice
+
+```al
+// CORRECT: page delegates to codeunit
+trigger OnAction()
+begin
+    SVManagement.RecalculateLine(Rec);
+end;
+```
+
+```al
+// CORRECT: validation belongs in table or codeunit
+trigger OnValidate()
+begin
+    SVManagement.ValidateAndRecalculate(Rec);
+end;
+```
+
+The codeunit owns the logic. The page owns the presentation.