126 lines
4.2 KiB
Markdown
126 lines
4.2 KiB
Markdown
# Contract: Import / Export Workflows
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Version: 1.0
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## Import Workflow
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Recommended stages:
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1. `Upload`
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2. `Preview / Validate`
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3. `Confirm`
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4. `Execute`
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5. `Result summary`
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Rules:
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- Validation preview must be human-readable (table/list), not raw JSON only.
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- Warnings and errors should be shown per row and in aggregate summary.
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- Confirm step should clearly communicate scope and side effects.
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## Export Workflow
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- User must explicitly choose export scope (`selected`, `filtered`, `all`) when ambiguity exists.
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- Export format should be explicit (`csv`, `json`, etc.).
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- Download response must set:
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- `Content-Type: text/csv; charset=utf-8`
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- `Content-Disposition: attachment; filename="..."`
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## CSV Format Rules (Excel-compatible)
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These rules are **mandatory** whenever CSV is exported for spreadsheet users.
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### Encoding and BOM
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- Write UTF-8 BOM (`\xEF\xBB\xBF`) as the very first bytes of the response.
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- Without BOM, Excel on Windows opens UTF-8 CSV as ANSI and garbles Cyrillic/special characters.
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```go
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w.Write([]byte{0xEF, 0xBB, 0xBF})
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```
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### Delimiter
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- Use **semicolon** (`;`) as the field delimiter, not comma.
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- Excel in Russian/European locale uses semicolon as the list separator.
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- Comma-delimited files open as a single column in these locales.
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### Numbers
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- Write decimal numbers with a **comma** as the decimal separator: `1 234,56` — not `1234.56`.
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- Excel in Russian locale does not recognize period as a decimal separator in numeric cells.
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- Format integers and floats explicitly; do not rely on Go's default `%v` or `strconv.FormatFloat`.
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- Use a thin non-breaking space (`\u202F`) or regular space as a thousands separator when the value
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benefits from readability (e.g. prices, quantities > 9999).
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```go
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// correct
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fmt.Sprintf("%.2f", price) // then replace "." -> ","
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strings.ReplaceAll(fmt.Sprintf("%.2f", price), ".", ",")
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// wrong — produces "1234.56", Excel treats it as text in RU locale
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fmt.Sprintf("%.2f", price)
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```
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### Dates
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- Write dates as `DD.MM.YYYY` — the format Excel in Russian locale parses as a date cell automatically.
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- Do not use ISO 8601 (`2006-01-02`) for user-facing CSV; it is not auto-recognized as a date in RU locale.
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### Text quoting
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- Wrap any field that contains the delimiter (`;`), a newline, or a double-quote in double quotes.
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- Escape embedded double-quotes by doubling them: `""`.
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- Use `encoding/csv` with `csv.Writer` and set `csv.Writer.Comma = ';'`; it handles quoting automatically.
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## Streaming Export Architecture (Go)
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For exports with potentially large row counts use a 3-layer streaming pattern.
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Never load all rows into memory before writing — stream directly to the response writer.
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```
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Handler → sets HTTP headers + writes BOM → calls Service
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Service → delegates to Repository with a row callback
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Repository → queries in batches → calls callback per row
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Handler/Service → csv.Writer.Flush() after all rows
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```
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```go
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// Handler
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func ExportCSV(c *gin.Context) {
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c.Header("Content-Type", "text/csv; charset=utf-8")
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c.Header("Content-Disposition", `attachment; filename="export.csv"`)
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c.Writer.Write([]byte{0xEF, 0xBB, 0xBF}) // BOM
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w := csv.NewWriter(c.Writer)
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w.Comma = ';'
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w.Write([]string{"ID", "Name", "Price"}) // header row
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err := svc.StreamRows(ctx, filters, func(row Row) error {
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return w.Write([]string{row.ID, row.Name, formatPrice(row.Price)})
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})
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w.Flush()
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if err != nil {
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// headers already sent — log only, cannot change status
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slog.Error("csv export failed mid-stream", "err", err)
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}
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}
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// Repository — batch fetch with callback
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func (r *Repo) StreamRows(ctx, filters, fn func(Row) error) error {
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rows, err := r.db.QueryContext(ctx, query, args...)
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// ... scan and call fn(row) for each row
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}
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```
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- Use `JOIN` in the repository query to avoid N+1 per row.
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- Batch size is optional; streaming row-by-row is fine for most datasets.
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- Always call `w.Flush()` after the loop — `csv.Writer` buffers internally.
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## Error Handling
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- Import errors should map to clear user-facing messages.
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- Export errors after streaming starts must be logged server-side only — HTTP headers are already
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sent and the status code cannot be changed mid-stream.
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