go 69 lines · 8 steps

Parsing CSV into typed structs in Go

A header-driven CSV parser that maps columns by name and converts each field into a strongly typed Product.

Explained by highlit
Intermediate csv-parsing error-wrapping type-conversion column-mapping
1package inventory
2 
3import (
4 "encoding/csv"
5 "fmt"
6 "io"
7 "strconv"
8 "strings"
9 "time"
10)
11 
12type Product struct {
13 SKU string
14 Name string
15 Price float64
16 InStock int
17 UpdatedAt time.Time
18}
19 
20func ParseProducts(r io.Reader) ([]Product, error) {
21 reader := csv.NewReader(r)
22 reader.TrimLeadingSpace = true
23 
24 header, err := reader.Read()
25 if err != nil {
26 return nil, fmt.Errorf("read header: %w", err)
27 }
28 
29 cols := make(map[string]int, len(header))
30 for i, name := range header {
31 cols[strings.ToLower(strings.TrimSpace(name))] = i
32 }
33 
34 var products []Product
35 for line := 2; ; line++ {
36 record, err := reader.Read()
37 if err == io.EOF {
38 break
39 }
40 if err != nil {
41 return nil, fmt.Errorf("line %d: %w", line, err)
42 }
43 
44 price, err := strconv.ParseFloat(record[cols["price"]], 64)
45 if err != nil {
46 return nil, fmt.Errorf("line %d: invalid price: %w", line, err)
47 }
48 
49 stock, err := strconv.Atoi(record[cols["in_stock"]])
50 if err != nil {
51 return nil, fmt.Errorf("line %d: invalid stock: %w", line, err)
52 }
53 
54 updated, err := time.Parse(time.RFC3339, record[cols["updated_at"]])
55 if err != nil {
56 return nil, fmt.Errorf("line %d: invalid timestamp: %w", line, err)
57 }
58 
59 products = append(products, Product{
60 SKU: record[cols["sku"]],
61 Name: record[cols["name"]],
62 Price: price,
63 InStock: stock,
64 UpdatedAt: updated,
65 })
66 }
67 
68 return products, nil
69}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Mapping header names to column indexes decouples parsing from physical column order.
  2. 2Wrapping errors with %w and a line number turns a parse failure into an actionable message.
  3. 3Converting each field at read time yields a fully typed struct instead of raw strings.

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