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bible/rules/patterns/import-export/contract.md
2026-04-02 13:48:36 +03:00

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# Contract: Import / Export Workflows
Version: 1.0
See `README.md` for the reference export handler and locale examples.
## Import Rules
- Recommended flow: `Upload -> Preview / Validate -> Confirm -> Execute -> Result summary`.
- Validation preview must be human-readable.
- Warnings and errors should be visible per row and in aggregate.
- The confirm step must communicate scope and side effects clearly.
## Export Rules
- The user must explicitly choose export scope when ambiguity exists, such as `selected`, `filtered`, or `all`.
- Export format must be explicit.
- Download responses must set `Content-Type` and `Content-Disposition` correctly.
## CSV Rules
- For spreadsheet-facing CSV, write UTF-8 BOM as the first bytes.
- Use semicolon `;` as the CSV delimiter.
- Use comma as the decimal separator for user-facing numeric values.
- Use `DD.MM.YYYY` for user-facing dates.
- Use `encoding/csv` with `csv.Writer.Comma = ';'` so quoting and escaping stay correct.
## Streaming Rules
- Large exports must stream rows directly to the response. Do not load the full dataset into memory first.
- Use the canonical flow:
`Handler -> Service -> Repository callback -> csv.Writer`
- Repository queries should avoid N+1 by using JOINs or another batched shape.
- Always call `csv.Writer.Flush()` after writing rows.
## Error Handling
- Import errors must map to clear user-facing messages.
- Once streaming has started, export failures are logged server-side only. Do not try to change the HTTP status after headers/body bytes were already sent.