import "github.com/farsil/null"

null is a Go package which aims to provide a reasonable way to deal with undefined values. It defines wrapper types that hold a boolean flag to specify whether the wrapped type is valid or not. The validity flag is used during marshaling (unmarshaling) to decide whether an undefined value should be marshaled (unmarshaled) in lieu of the underlying value. The undefined value varies according to the specific serialization interface:

• With JSON, the undefined value is the JSON string null
• With SQL, the undefined value is the SQL value NULL
• With flag, the undefined value is ""
• With the default text encoding, the undefined value is an empty []byte

Types in the package implement all the necessary interfaces to be used with the flag package, to handle JSON and SQL NULL values, so it can be used in place of the sql.Nullxxx types. The interfaces implemented by each type are:

• TextMarshaler from encoding
• TextUnmarshaler from encoding
• Marshaler from encoding/json
• Unmarshaler from encoding/json
• Value from flag
• Scanner from database/sql
• Valuer from database/sql/driver
• Stringer from fmt (as part of the Value interface from flag)

Installation is as simple as invoking:

$ go get github.com/farsil/null

The package defines the following data types:

• null.String which wraps a string
• null.Bool which wraps a bool
• null.Int which wraps an int
• null.Uint which wraps an uint
• null.Float64 which wraps a float64
• null.Time which wraps a time.Time

Note that JSON does not define a standard datetime representation. In this package, a null.Time object is represented as an RFC3339 string when a null.Time object is marshaled, and an RFC3339 string is parsed when unmarshaling from JSON.

package main

import "github.com/farsil/null"

var data = []byte(`{
    "title": "The foo does a bar"
}`)

type BookTitle struct {
	Title    null.String `json:"title"`
	Subtitle null.String `json:"subtitle"`
}

func main() {
	var t Title
	if err := json.Unmarshal(data, &t); err != nil {
		// process error
	}

	if !t.Title.Valid {
		fmt.Println("Book has no title")
		return
	}

	fmt.Println("Book title:", t.Title.Str)

	if t.Subtitle.Valid {
		fmt.Println("Book subtitle:", t.Subtitle.Str)
	} else {
		fmt.Println("Book has no subtitle")
	}
}

Output

Book title: 'The foo does a bar'
Book has no subtitle

The documentation is available at the address https://godoc.org/github.com/farsil/null.

This repository is heavily inspired by https://github.com/guregu/null. I originally wanted to create a fork of that repository, but since there are critical incompatibilities of interfaces and behavior, I decided to start from scratch.