feat: Enhance user update handling and introduce NullString type for optional fields

backend/internal/dtos/common.go

@@ -0,0 +1,33 @@
+package dto
+
+import "encoding/json"
+
+type NullString struct {
+	String string
+	IsNull bool
+}
+
+// Serialization
+func (ns NullString) MarshalJSON() ([]byte, error) {
+	// If Valid is true, return the JSON serialization result of String.
+	if ns.IsNull {
+		return []byte(`"` + ns.String + `"`), nil
+	}
+	// If Valid is false, return the serialization result of null.
+	return []byte("null"), nil
+}
+
+// Deserialization
+func (ns *NullString) UnmarshalJSON(data []byte) error {
+	// If data is null, set Valid to false and String to an empty string.
+	if string(data) == "null" {
+		ns.String, ns.IsNull = "", false
+		return nil
+	}
+	// Otherwise, deserialize data to String and set Valid to true.
+	if err := json.Unmarshal(data, &ns.String); err != nil {
+		return err
+	}
+	ns.IsNull = true
+	return nil
+}

backend/internal/dtos/user_dto.go

@@ -11,7 +11,7 @@ type UserDto struct {
 	LastEditorID string    `json:"lastEditorID" example:"01HGW2BBG0000000000000000"`
 	Email        string    `json:"email" example:"test@example.com"`
 	Role         string    `json:"role" example:"admin"`
-	CompanyID    string    `json:"companyId" example:"01HGW2BBG0000000000000000"`
+	CompanyID    *string   `json:"companyId" example:"01HGW2BBG0000000000000000"`
 	HourlyRate   float64   `json:"hourlyRate" example:"50.00"`
 }
 
@@ -19,7 +19,7 @@ type UserCreateDto struct {
 	Email      string  `json:"email" example:"test@example.com"`
 	Password   string  `json:"password" example:"password123"`
 	Role       string  `json:"role" example:"admin"`
-	CompanyID  string  `json:"companyId" example:"01HGW2BBG0000000000000000"`
+	CompanyID  *string `json:"companyId" example:"01HGW2BBG0000000000000000"`
 	HourlyRate float64 `json:"hourlyRate" example:"50.00"`
 }