How to Split a JSON Field into a String Slice During Unmarshaling in Golang?

Custom Unmarshal with String Split in Golang

Problem:

Handling JSON unmarshalling when one field requires splitting into a slice using string operations. Specifically, the "subjects" field in the provided JSON requires splitting on '-' to create a []string.

Solution:

To achieve this, we can define a custom string slice type and implement the json.Unmarshaler interface for it. Here's how:

<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>

This custom type will allow us to unmarshal the "subjects" field as a string and then automatically split it into a slice.

Revised Struct:

Now, we can update our Student struct to use the custom strslice type for the "subjects" field:

<code class="go">type Student struct {
    StudentNumber int      `json:"student_number"`
    Name          string   `json:"name"`
    Subjects      strslice `json:"subjects"`
}</code>

Usage:

With these modifications, we can now unmarshal the provided JSON and have the "subjects" field automatically split:

<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>

This approach provides a clean and customizable way to handle field transformations while unmarshalling JSON data.

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