Example custom type to JSON

internal/data/movies.go

@@ -9,7 +9,13 @@ type Movie struct {
 	CreatedAt time.Time `json:"-"` // omits always
 	Title     string    `json:"title"`
 	Year      int32     `json:"year,omitzero"`
-	Runtime   int32     `json:"runtime,omitzero"`
-	Genres    []string  `json:"genres,omitzero"`
-	Version   int32     `json:"version"`
+	// Runtime   int32     `json:"runtime,omitzero"`
+	// Use the Runtime type instead of int32. Note that the omitzero directive will
+	// still work on this: if the Runtime field has the underlying value 0, then it will
+	// be considered zero and omitted -- and the MarshalJSON() method we just made
+	// won't be called at all.
+	// VSCode will complain though about reflection issue
+	Runtime Runtime  `json:"runtime,omitzero`
+	Genres  []string `json:"genres,omitzero"`
+	Version int32    `json:"version"`
 }

internal/data/types.go

@@ -0,0 +1,27 @@
+package data
+
+import (
+	"fmt"
+	"strconv"
+)
+
+// Declare a custom Runtime type, which has the underlying int32 type
+type Runtime int32
+
+// The rule about pointers vs. values for receivers is that value methods
+//  can be invoked on pointers and values, but pointer methods can only
+// be invoked on pointers.
+
+// Implements json.Marshaler interface.
+func (r Runtime) MarshalJSON() ([]byte, error) {
+	// Generate a string containing the movie runtime
+	jsonValue := fmt.Sprintf("%d mins", r)
+
+	//Use strconv.Quote() function on the string to wrap it in double quotes
+	// necessary to be valid json
+	quotedJSONValue := strconv.Quote(jsonValue)
+
+	// convert the string to byte slice and return it
+
+	return []byte(quotedJSONValue), nil
+}