optnull

optnull is a Go package that provides OptNull, a type that can represent optional, nullable JSON values.

OptNull is designed to be used with encoding/json Marshal. It can represent JSON values that may be empty, null, or have a value.

Example

type User struct {
    ID    string                     `json:"id"`
    Name  optnull.OptNull[string]    `json:"name,omitempty"`
    Age   optnull.OptNull[int]       `json:"age,omitempty"`
    Birth optnull.OptNull[time.Time] `json:"birth,omitempty"`
}

var u User
_ = json.Unmarshal([]byte(`{"id":"123","name":"Alice","age":null}`), &u)
fmt.Println(u.Name.HasValue(), u.Age.Null(), u.Birth.Empty()) // true true true
fmt.Println(u.Name.String()) // Alice

Motivation

The idea to create this package was to be used in PATCH HTTP requests. Imagine you have a /users/:userID endpoint which accepts the PATCH method. A user is represented with a JSON such as {"id": "123", "name": "Alice", "age": 23, "birth": "2001-06-21T00:00:00Z"}. Fields other than id are optional. A PATCH request may, for each optional field, (a) modify its value, (b) unset its value, or (c) do nothing. For example, a PATCH request to /users/123 with body {"name": "John"} sets the name to "John", a body of {"name": null} sets the name to null and {"age": 33} does not modify the name.

Using native types and the encoding/json package it is not possible to distinguish in a Go backend service between the omitted and null values. This package offers a way to do that.