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Repair broken knowledge references and align review examples with canonical articles. Correct explicit version gates, restore a missing title, and recognize the plugin directory in the root guard. Co-authored-by: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com> Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
30 lines
1.8 KiB
Markdown
30 lines
1.8 KiB
Markdown
---
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bc-version: [21..]
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domain: upgrade
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keywords: [datatransfer, large-dataset, bulk-update, modifyall, copyfields, new-field]
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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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# Use `DataTransfer` for bulk updates on large tables
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## Description
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Tables that can contain more than 300,000 records, and any newly added field on an existing table, should be initialized with `DataTransfer` rather than a `repeat ... Modify ... until Next() = 0` loop. `DataTransfer` issues a single set-based statement to the database; the loop/modify pattern issues one round-trip per row and accumulates write locks for the duration of the upgrade. On the volumes that drive upgrade pain — ledger entries, item ledger entries, price list lines — the difference is the upgrade running for minutes instead of hours.
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## Best Practice
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For a bulk update use a `DataTransfer` variable: call `SetTables(Database::"...", Database::"...")` (source and destination may be the same table), add filters with `AddSourceFilter`, set the target value with `AddConstantValue` (or copy a source field with `AddFieldValue`), and execute with `CopyFields()`. To express multiple distinct updates against the same table, `Clear` the `DataTransfer` between executions and configure the next one.
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See sample: `datatransfer-for-bulk-init.good.al`.
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## Anti Pattern
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Iterating with `FindSet(true) ... repeat ... Modify() ... until Next() = 0` to set a single field across an entire large table. On 300k+ rows this is the canonical slow-upgrade footgun.
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See sample: `datatransfer-for-bulk-init.bad.al`.
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## See also
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- `datatransfer-skips-triggers-and-subscribers.md` — `DataTransfer` does not raise field validation triggers or event subscribers; if a row needs validation logic, `DataTransfer` is the wrong tool.
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