Unmarshal CSV record into struct in Go

The problem how to automatically deserialize/unmarshal record from CSV file into Go struct.

For example, I have

type Test struct {
  Name string
  Surname string
  Age int
}

And CSV file contains records

John;Smith;42
Piter;Abel;50

Is there an easy way to unmarshal those records into struct except by using "encoding/csv" package for reading record and then doing something like

record, _ := reader.Read()
test := Test{record[0],record[1],atoi(record[2])}

There is gocarina/gocsv which handles custom struct in the same way encoding/json does.
You can also write custom marshaller and unmarshaller for specific types.

Example:

type Client struct {
	Id      string `csv:"client_id"` // .csv column headers
	Name    string `csv:"client_name"`
	Age     string `csv:"client_age"`
}

func main() {
	in, err := os.Open("clients.csv")
	if err != nil {
		panic(err)
	}
	defer in.Close()

	clients := []*Client{}

   	if err := gocsv.UnmarshalFile(in, &clients); err != nil {
		panic(err)
	}
	for _, client := range clients {
		fmt.Println("Hello, ", client.Name)
	}
}

Seems I've done with automatic marshaling of CSV records into structs (limited to string and int). Hope this would be useful.

Here is a link to playground: http://play.golang.org/p/kwc32A5mJf

func Unmarshal(reader *csv.Reader, v interface{}) error {
	record, err := reader.Read()
	if err != nil {
		return err
	}
	s := reflect.ValueOf(v).Elem()
	if s.NumField() != len(record) {
		return &FieldMismatch{s.NumField(), len(record)}
	}
	for i := 0; i < s.NumField(); i++ {
		f := s.Field(i)
		switch f.Type().String() {
		case "string":
			f.SetString(record[i])
		case "int":
			ival, err := strconv.ParseInt(record[i], 10, 0)
			if err != nil {
				return err
			}
			f.SetInt(ival)
		default:
			return &UnsupportedType{f.Type().String()}
		}
	}
	return nil
}

I'll try to create github package is someone needs this implementation.

You could bake your own. Perhaps something like this:

package main

import (
	"fmt"
	"strconv"
	"strings"
)

type Test struct {
	Name    string
	Surname string
	Age     int
}

func (t Test) String() string {
	return fmt.Sprintf("%s;%s;%d", t.Name, t.Surname, t.Age)
}

func (t *Test) Parse(in string) {
	tmp := strings.Split(in, ";")
	t.Name = tmp[0]
	t.Surname = tmp[1]
	t.Age, _ = strconv.Atoi(tmp[2])
}

func main() {

	john := Test{"John", "Smith", 42}
	fmt.Printf("john:%v\n", john)

	johnString := john.String()
	fmt.Printf("johnString:%s\n", johnString)

	var rebornJohn Test
	rebornJohn.Parse(johnString)
	fmt.Printf("rebornJohn:%v\n", rebornJohn)

}

Using csvutil it is possible to give column header see example.

In your case, this could be :

package main

import (
	"encoding/csv"
	"fmt"
	"io"
	"os"

	"github.com/jszwec/csvutil"
)

type Test struct {
	Name    string
	Surname string
	Age     int
}

func main() {
	csv_file, _ := os.Open("test.csv")
	reader := csv.NewReader(csv_file)
	reader.Comma = ';'

	userHeader, _ := csvutil.Header(Test{}, "csv")
	dec, _ := csvutil.NewDecoder(reader, userHeader...)

	var users []Test
	for {
		var u Test
		if err := dec.Decode(&u); err == io.EOF {
			break
		}
		users = append(users, u)
	}

	fmt.Println(users)
}

A simple way to solve the problem is to use JSON as an intermediate representation.

Once you've done this, you have a variety of tools at your disposal.

You can...

• Unmarshal directly to your type (if it's all strings)
• Unmarshal to a map[string]interface{} and then make any necessary type conversions
• Unmarshal -> convert types -> remarshal JSON -> unmarshal to your type

Here's a simple generic marshalling function that enables this flow...

pairToJSON := func(header, record []string) string {
	raw := ""
	for j, v := range record {
		if j != 0 {
			raw += ",\n"
		}
		raw += "\"" + header[j] + "\":\"" + v + "\""
	}
	raw = "{\n" + raw + "\n}"
	return raw
}

The above is compatible with the []string data produced by the standard csv library.