README
¶
modtracker
JSON unmarshaling in Go that includes detection of the fields that were modified during unmarshaling
If you are doing a CRUD update via a REST API using JSON, you probably only want to update the database fields that were actually sent by the client. The standard Go JSON Unmarshaler doesn't provide this information.
The modtracker package provides a way to discover this information. You can use it in a few ways. First, you can call modtracker.UnmarshalJSON directly:
type Sample struct {
FirstName *string
LastName *string
Age *int
}
func main() {
var s Sample
data := `
{
"FirstName": "Homer",
"LastName": "Simpson",
"Age": 37
}
`
fmt.Println("converting", data)
modified, err := modtracker.Unmarshal([]byte(data), &s)
if err != nil {
fmt.Printf("%+v\n", err)
} else {
fmt.Println(s,modified)
}
}
You can wrap the call to modtracker.Unmarshal inside of an UnmarshalJSON method:
type Sample struct {
FirstName *string
LastName *string
Age *int
modified []string
}
func (s *Sample) UnmarshalJSON(data []byte) error {
var err error
s.modified, err = modtracker.Unmarshal(data, s)
return err
}
func (s *Sample) GetModified() []string {
return s.modified
}
func main() {
var s Sample
data := `
{
"FirstName": "Homer",
"LastName": "Simpson",
"Age": 37
}
`
fmt.Println("converting", data)
err := json.Unmarshal([]byte(data), &s)
if err != nil {
fmt.Printf("%+v\n", err)
} else {
fmt.Println(s)
}
}
You can avoid some of the cost of reflection by pre-caclulating the fields, tags, and types using the BuildJSONUnmarshaler function:
var sampleUnmarshaler modtracker.Unmarshaler
func init() {
var err error
sampleUnmarshaler, err = modtracker.BuildJSONUnmarshaler((*Sample)(nil))
if err != nil {
panic(err)
}
}
type Sample struct {
FirstName *string
LastName *string
Age *int
modified []string
}
func (s *Sample) UnmarshalJSON(data []byte) error {
var err error
s.modified, err = sampleUnmarshaler(data, s)
return err
}
func (s *Sample) GetModified() []string {
return s.modified
}
func main() {
var s Sample
data := `
{
"FirstName": "Homer",
"LastName": "Simpson",
"Age": 37
}
`
fmt.Println("converting", data)
err := json.Unmarshal([]byte(data), &s)
if err != nil {
fmt.Printf("%+v\n", err)
} else {
fmt.Println(s)
}
}
The modtracker unmarshalers respect json struct tags and work with both pointer and value fields. Fields of function type and channel type are ignored.
Contributors:
We welcome your interest in Capital One’s Open Source Projects (the “Project”). Any Contributor to the project must accept and sign a CLA indicating agreement to the license terms. Except for the license granted in this CLA to Capital One and to recipients of software distributed by Capital One, you reserve all right, title, and interest in and to your contributions; this CLA does not impact your rights to use your own contributions for any other purpose.
This project adheres to the Open Source Code of Conduct. By participating, you are expected to honor this code.
Documentation
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Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func BuildJSONUnmarshaler ¶
BuildJSONUnmarshaler generates a custom implementation of the Unmarshaler type for the type of the provided struct. The preferred way to use BuildJSONUnmarshaler is to create a package-level variable and assign it in init with a nil instance of the type:
type Sample struct {
FirstName *string
LastName *string
Age *int
Inner *struct {
Address string
}
Pet string
Company string `json:"company"`
modified []string
}
var sampleUnmarshaler modtracker.Unmarshaler
func init() {
var err error
sampleUnmarshaler, err = modtracker.BuildJSONUnmarshaler((*Sample)(nil))
if err != nil {
panic(err)
}
}
func (s *Sample) UnmarshalJSON(data []byte) error {
modified, err := sampleUnmarshaler(data, s)
if err != nil {
return err
}
s.modified = modified
return nil
}
func UnmarshalJSON ¶
UnmarshalJSON provides the default implementation of the Unmarshaler type. It will rediscover the fields in the structure each time it is called; to improve performance, use BuildJSONUnmarshaler to create an Unmarshaler instance with the struct fields pre-calculated.
Types ¶
type Modifiable ¶
type Modifiable interface {
GetModified() []string
}
Modifiable is implemented by struct types that contain a list of their fields that were populated from JSON. If a value for a field, even null, was provided in the JSON, the name of the field appears in the slice of strings.
type Unmarshaler ¶
An Unmarshaler takes in JSON in the first parameter, a pointer to a struct in the second parameter, populates the struct with the JSON and returns the modified fields as a slice of strings. In case of error, the struct might be partially populated. If there is an error, the modified field slice will be nil.
Source Files
Directories