toJson method is throwing me an error on call - json

Question

I may need help with this. Basically im getting this exception when calling order.toJson() method. I have been checking the code but seems good for me. If you see an error please let me know.
E/flutter ( 5623): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception:
Converting object to an encodable object failed: Instance of 'OrderItem'
E/flutter ( 5623): #0 _JsonStringifier.writeObject (dart:convert/json.dart:688:7)
E/flutter ( 5623): #1 _JsonStringifier.writeList (dart:convert/json.dart:736:7)
E/flutter ( 5623): #2 _JsonStringifier.writeJsonValue (dart:convert/json.dart:718:7)
E/flutter ( 5623): #3 _JsonStringifier.writeObject (dart:convert/json.dart:679:9)
E/flutter ( 5623): #4 _JsonStringStringifier.printOn (dart:convert/json.dart:877:17)
E/flutter ( 5623): #5 _JsonStringStringifier.stringify (dart:convert/json.dart:862:5)
E/flutter ( 5623): #6 JsonEncoder.convert (dart:convert/json.dart:262:30)
E/flutter ( 5623): #7 JsonCodec.encode (dart:convert/json.dart:172:45)
When calling toJson() method. Here are my classes.
class Order{
String id;
String userId;
String deliverId;
String restaurantId;
List<OrderItem> orderItems;
double total;
String orderStatus;
Order({
required this.id,
required this.userId,
required this.deliverId,
required this.restaurantId,
required this.orderItems,
required this.total,
required this.orderStatus
});
Map<String, dynamic> toJson(){
return {
'id' : id,
'userId' : userId,
'deliverId' : deliverId,
'restaurantId' : restaurantId,
'orderItems' : jsonEncode(orderItems),
'total' : total,
'orderStatus' : orderStatus
};
}
}
OrderItem class
class OrderItem{
RestaurantModel restaurant;
List<OrderProduct> products;
String id;
OrderItem({
required this.restaurant,
required this.products,
required this.id
});
Map<String, dynamic> toJson(){
return {
'restaurant' : restaurant.toJson(),
'products' : jsonEncode(products),
'id' : id,
};
}
}
RestaurantModel class
class RestaurantModel {
String uid;
String restaurantName;
String restaurantAddress;
String restaurantUrl;
String restaurantSlogan;
int stars;
String cost;
String category;
String status;
DateTime startDate;
List<Product>? products;
RestaurantModel({
required this.uid,
required this.restaurantName,
required this.restaurantAddress,
required this.restaurantSlogan,
required this.restaurantUrl,
required this.stars,
required this.cost,
required this.category,
required this.status,
required this.startDate,
this.products,
});
Map<String, Object?> toJson(){
return{
'restaurantName' : restaurantName,
'restaurantAddress' : restaurantAddress,
'restaurantSlogan' : restaurantSlogan,
'restaurantUrl': restaurantUrl,
'stars' : stars,
'cost' : cost,
'category' : category,
'status' : status,
'startDate' : startDate,
};
}
}
OrderProduct class
class OrderProduct{
Product product;
int quantity;
OrderProduct({
required this.product,
required this.quantity,
});
Map<String, dynamic> toJson(){
return {
'product' : product.toJson(),
'quantity' : quantity,
};
}
}
Product class
class Product{
String productId;
String productName;
String productDescription;
double productPrice;
String productUrl;
int productLikes;
String productUnit;
Product({
required this.productId,
required this.productName,
required this.productDescription,
required this.productPrice,
required this.productUrl,
required this.productLikes,
required this.productUnit,
}
);
Map<String, dynamic> toJson(){
return {
'productId' : productId,
'productName' : productName,
'productDescription' : productDescription,
'productPrice' : productPrice,
'productUrl' : productUrl,
'productLikes' : productLikes,
'productUnit' : productUnit,
};
}
}
So basically I'm getting an error when trying to call toJson() method from order.
void addOrderAsync(String userId, Order order) async{
// here is where im getting the error
final jsonData = order.toJson();
final response = await http.post(Uri.parse("$apiUrl/users/$userId/cart/add"),
headers: <String, String> {
'Content-Type': 'application/json; charset=UTF-8',
},
body: jsonEncode(jsonData),
);
if(response.statusCode == 200 || response.statusCode == 201){
// do something
}
else{
throw Exception("Failed to create user");
}
}

Answer 1

try change toJson() to:
Map<String, dynamic> toJson(){
final Map<String, dynamic> data = new Map<String, dynamic>();
data['productId'] = this.productId;
data['productName'] = this.productName;
data['productDescription'] = this.productDescription;
data['productPrice'] = this.productPrice;
data['productUrl'] = this.productUrl;
data['productLikes'] = this.productLikes;
data['productUnit'] = this.productUnit;
return data;
}

Answer 2

Try this:
Map<String, dynamic> toJson(){
return {
'id' : id,
'userId' : userId,
'deliverId' : deliverId,
'restaurantId' : restaurantId,
'orderItems' : orderItems.toJson(),
'total' : total,
'orderStatus' : orderStatus
};
}
Replace jsonEncode by toJson()