How to Unmarshal a JSON String into a Slice Using a Delimiter in Golang?

Custom Unmarshal with String Split in Golang

Problem:

Unmarshalling JSON into a struct with a field that should be a slice of strings, while the JSON value is a single string that needs to be split using a delimiter.

<code class="json">{
  "student_number": 1234567,
  "name": "John Doe",
  "subjects": "Chemistry-Maths-History-Geography"
}</code>

<code class="go">type Student struct {
  StudentNumber int
  Name          string
  Subjects      []string
}</code>

Answer:

Define a custom string slice type and implement json.Unmarshaler to handle the split:

<code class="go">type strslice []string

func (ss *strslice) UnmarshalJSON(data []byte) error {
  var s string
  if err := json.Unmarshal(data, &s); err != nil {
    return err
  }
  *ss = strings.Split(s, "-")
  return nil
}</code>

Use this custom type in the struct:

<code class="go">type Student struct {
  StudentNumber int
  Name          string
  Subjects      strslice
}</code>

Code Example:

<code class="go">func main() {
  var s Student
  err := json.Unmarshal([]byte(src), &s)
  fmt.Println(s, err)
}

const src = `{"student_number":1234567, "name":"John Doe", "subjects":"Chemistry-Maths-History-Geography"}`</code>

Output:

{1234567 John Doe [Chemistry Maths History Geography]} <nil></nil>

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