bcquality/microsoft/knowledge/performance/hidden-flowfields-still-calculate-before-bc26-opt-in.md
Jesper Schulz-Wedde e81632b4be Complete AL review knowledge readiness
Fill telemetry and Query coverage, strengthen thin review domains, correct audited content defects, and add deterministic cheap-model evaluation and reference-integrity safeguards.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 9825b012-e653-496a-9310-c1f4b6f8ac27
2026-07-15 07:19:15 +02:00

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---
bc-version: [all]
domain: performance
keywords: [flowfield, visible, page-control, calculate-only-visible-flowfields, feature-management, hidden-field]
technologies: [al]
countries: [w1]
application-area: [all]
---
# Hidden page FlowFields still calculate unless visible-only calculation is enabled
## Description
By default, a FlowField used directly as a page control's source is calculated when the page loads even when `Visible = false` or its visibility expression evaluates to false. The hidden control can therefore issue an aggregate query that no user sees. Business Central 26 introduced the **Calculate only visible FlowFields** feature-management option; only environments with that option enabled skip calculation for controls that are not visible.
## Best Practice
On BC 26 and later, enable and verify the visible-only FlowField feature before relying on `Visible` to suppress calculation. When the target environment does not guarantee that option, avoid binding an expensive FlowField directly to a usually-hidden control: calculate it only in the branch that displays it and bind the page control to a variable. Do not flag a hidden FlowField when the v26 feature is known to be enabled or the FlowField is cheap and intentionally preloaded.
See sample: `hidden-flowfields-still-calculate-before-bc26-opt-in.good.al`.
## Anti Pattern
Adding a costly Sum or Lookup FlowField to a page with `Visible = SomeRareMode` and assuming the hidden state prevents its query on all supported versions. The review signal is the direct FlowField source plus conditional or false visibility, not visibility alone.
See sample: `hidden-flowfields-still-calculate-before-bc26-opt-in.bad.al`.