Store struct as string in redis - json

Question

As Redis only stores strings I would like to know how I can do the equivalent of Javascript's JSON.stringify using Go to convert a Struct into a string.
I have tried typecasting:
string(the_struct)
but this results in an error.

Answer 1

The encoding/json package can be used to easily convert a struct to JSON string and vice versa (parse a JSON string into a struct).
Simple example (try it on the Go Playground):
type Person struct {
Name string
Age int
}
func main() {
p := Person{"Bob", 23}
// Struct -> JSON
data, err := json.Marshal(&p)
if err != nil {
panic(err)
}
fmt.Println(string(data))
// JSON -> JSON
var p2 Person
err = json.Unmarshal(data, &p2)
if err != nil {
panic(err)
}
fmt.Printf("%+v", p2)
}
Output:
{"Name":"Bob","Age":23}
{Name:Bob Age:23}
Notes:
The fields of the struct must be exported (start them with capital letter), else the json package (which uses reflection) will not be able to read/write them.
You can also specify tags for the struct fields to control/fine tune the json marshaling/unmarshaling process, for example to change the names in the JSON text:
type Person struct {
Name string `json:"name"`
Age int `json:"years"`
}
With this change the output of the above application is the following:
{"name":"Bob","years":23}
{Name:Bob Age:23}
The documentation of the json.Marshal() function details the possibilities provided by the tags.
And by implementing the json.Marshaler and json.Unmarshaler interfaces you can fully customize the marshaling / unmarshaling process.
Also if your struct is not pre-defined (e.g. you don't know the fields in advance), you can use a map[string]interface{}. See this answer for details and examples.