bcquality/microsoft/knowledge/performance/do-not-modify-in-onaftergetrecord.md

bc-version	domain	keywords	technologies	countries	application-area
all	performance	page-trigger onaftergetrecord modify display scroll db-write	al	w1	all

Do not Modify inside OnAfterGetRecord

Description

A list page's OnAfterGetRecord fires once per visible row, every time the user scrolls, sorts, or refreshes. A Modify inside that trigger means a database write per row displayed. Per the upstream guidance, "Modify() here means a DB write on every scroll. Use page variables for display-only state instead." OnAfterGetCurrRecord (single record on selection), OnOpenPage, and OnInit fire once or at much lower frequency and tolerate one-time setup logic.

Best Practice

When the trigger needs to compute display-only state per row, write the result into a page variable (a global on the page object) rather than back to the database. Reserve Modify for triggers that fire on an explicit user action — OnAction, validation triggers, OnQueryClosePage — where one action maps to one write.

See sample: do-not-modify-in-onaftergetrecord.good.al.

Anti Pattern

trigger OnAfterGetRecord() begin Rec."Warning Flag" := CalcWarning(); Rec.Modify(); end; — on a list page over a moderately sized table, scrolling through fifty rows produces fifty writes. The page feels slow, the table accumulates churn, and the warning flag — which is recomputed on every refresh anyway — never needed persistence.

See sample: do-not-modify-in-onaftergetrecord.bad.al.