flutter add data to json only if it does not already exist - flutter

Question

I have following Model
product_model.dart
class ProductModel {
String status;
String message;
List<Results> results;
ProductModel({this.status, this.message, this.results});
ProductModel.fromJson(Map<String, dynamic> json) {
status = json['status'];
message = json['message'];
if (json['data'] != null) {
results = new List<Results>();
json['data'].forEach((v) {
results.add(new Results.fromJson(v));
});
}
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = new Map<String, dynamic>();
data['status'] = this.status;
data['message'] = this.message;
if (this.results != null) {
data['data'] = this.results.map((v) => v.toJson()).toList();
}
return data;
}
}
class Results {
String id;
String productCode;
String category;
String title;
String isActive;
Results(
{this.id,
this.productCode,
this.category,
this.title,
this.isActive,
});
Results.fromJson(Map<String, dynamic> json) {
id = json['id'];
productCode = json['product_code'];
category = json['category'];
title = json['title'];
isActive = json['is_active'];
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = new Map<String, dynamic>();
data['id'] = this.id;
data['product_code'] = this.productCode;
data['title'] = this.title;
data['category'] = this.category;
data['is_active'] = this.isActive;
return data;
}
}
I have a functionality to save products to favorites. The favorites will be saved as json in a file.
import 'package:example/utils/favstorage.dart';
import 'package:example/models/product_model.dart';
class FavoriteProducts {
FavoritesStorage storage = FavoritesStorage();
List<ProductModel> favorites = [];
Future addFavorite(ProductModel products) async {
favorites.add(products);
await storage.writeFavorites(favorites);
}
}
I want to add product to favorites only if its not there. How can I update the addFavorite method so that if particular id doesnot exist then only proceed adding to favorites.
I am new to flutter. Can anybody help me on this??

Answer 1

You can use and indexWhere to search your list for an item with the same id, like this:
Future addFavorite(ProductModel products) async {
if(favorites.indexWhere((listProduct) => listProduct.id == products.id) == -1){
favorites.add(products);
await storage.writeFavorites(favorites);
}
}
-1 means there was no item, if there was the item it would have returned it from the list.

Answer 2

Understanding your model:
ProductModel has List
Results has id.
How to see if provided ProductModel can be added to favorite:
Take favorites list and look in List.
in each product model liik in List.
for each Results check if there id is same as any Results in List of provided ProductModel to the method.
If every thing is false, add ProductModel to favorite.
Following is the code for your reference:
Future addFavorite(ProductModel products) async {
bool containsId = favorites.any((ProductModel model){
return model.results.any((Results result){
return products.results.any((Results resultInProducts) => resultInProducts.id == result.id);
});
});
if(!containsId){
favorites.add(products);
await storage.writeFavorites(favorites);
}
}
I hope this helps, in case of any doubt please comment. If this answer helps you then please accept and up-vote the answer.