Go CSV

The GoCSV package aims to provide easy serialization and deserialization functions to use CSV in Golang

API and techniques inspired from https://godoc.org/gopkg.in/mgo.v2

Installation

go get -u github.com/gocarina/gocsv

Full example

Consider the following CSV file

client_id,client_name,client_age
1,Jose,42
2,Daniel,26
3,Vincent,32

Easy binding in Go!

package main

import (
	"fmt"
	"os"

	"github.com/gocarina/gocsv"
)

type NotUsed struct {
	Name string
}

type Client struct { // Our example struct, you can use "-" to ignore a field
	Id            string `csv:"client_id"`
	Name          string `csv:"client_name"`
	Age           string `csv:"client_age"`
	NotUsedString string `csv:"-"`
	NotUsedStruct NotUsed `csv:"-"` 
}

func main() {
	clientsFile, err := os.OpenFile("clients.csv", os.O_RDWR|os.O_CREATE, os.ModePerm)
	if err != nil {
		panic(err)
	}
	defer clientsFile.Close()

	clients := []*Client{}

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

	if _, err := clientsFile.Seek(0, 0); err != nil { // Go to the start of the file
		panic(err)
	}

	clients = append(clients, &Client{Id: "12", Name: "John", Age: "21"}) // Add clients
	clients = append(clients, &Client{Id: "13", Name: "Fred"})
	clients = append(clients, &Client{Id: "14", Name: "James", Age: "32"})
	clients = append(clients, &Client{Id: "15", Name: "Danny"})
	csvContent, err := gocsv.MarshalString(&clients) // Get all clients as CSV string
	//err = gocsv.MarshalFile(&clients, clientsFile) // Use this to save the CSV back to the file
	if err != nil {
		panic(err)
	}
	fmt.Println(csvContent) // Display all clients as CSV string

}

Customizable Converters

type DateTime struct {
	time.Time
}

// Convert the internal date as CSV string
func (date *DateTime) MarshalCSV() (string, error) {
	return date.Time.Format("20060201"), nil
}

// You could also use the standard Stringer interface 
func (date *DateTime) String() (string) {
	return date.String() // Redundant, just for example
}

// Convert the CSV string as internal date
func (date *DateTime) UnmarshalCSV(csv string) (err error) {
	date.Time, err = time.Parse("20060201", csv)
	return err
}

type Client struct { // Our example struct with a custom type (DateTime)
	Id       string   `csv:"id"`
	Name     string   `csv:"name"`
	Employed DateTime `csv:"employed"`
}

Nested structs

When decoding nested pointer structs, GoCSV allocates the pointers needed to reach each field. An omitempty field still omits an empty leaf pointer value; it does not prevent allocation of the enclosing structs.

By default, the fields of nested structs are prefixed with the parent field's name. For example:

type Foo struct {
	B Bar
	X int `csv:"x"`
}

type Bar struct {
	A int `csv:"a"`
	B int `csv:"b"`
}

produces columns B.a, B.b, x.

Use the csv:"." tag to inline the nested struct's fields without that prefix; for example:

type Foo struct {
	B Bar `csv:"."`
	X int `csv:"x"`
}

type Bar struct {
	A int `csv:"a"`
	B int `csv:"b"`
}

produces columns a, b, x.

Customizable CSV Reader / Writer

func main() {
        ...
	
        gocsv.SetCSVReader(func(in io.Reader) gocsv.CSVReader {
            r := csv.NewReader(in)
            r.Comma = '|'
            return r // Allows use pipe as delimiter
        })	
	
        ...
	
        gocsv.SetCSVReader(func(in io.Reader) gocsv.CSVReader {
            r := csv.NewReader(in)
            r.LazyQuotes = true
            r.Comma = '.'
            return r // Allows use dot as delimiter and use quotes in CSV
        })
	
        ...
	
        gocsv.SetCSVReader(func(in io.Reader) gocsv.CSVReader {
            //return csv.NewReader(in)
            return gocsv.LazyCSVReader(in) // Allows use of quotes in CSV
        })

        ...

        gocsv.UnmarshalFile(file, &clients)

        ...

        gocsv.SetCSVWriter(func(out io.Writer) *gocsv.SafeCSVWriter {
            writer := csv.NewWriter(out)
            writer.Comma = '|'
            return gocsv.NewSafeCSVWriter(writer)
        })

        ...

        gocsv.MarshalFile(&clients, file)

        ...
}