C# JSON Serialize/Deserialize - INPUT problem

Question

I have problem with serialization and deserialization in JSON I've made 2 tasks to read from JSON file which looks like this:

[
  {
    "ID": 1,
    "OIB": 123456789,
    "ime": "name",
    "prezime": "surname",
    "grad": "city"
  }
]

Now I have to add another client with ID 2, with new user informations. I can read this JSON file with no problems, but I am stuck on writing into the same file.

public struct Klijent
{
    public int ID { get; set; }
    public long OIB { get; set; }
    public string ime { get; set; }
    public string prezime { get; set; }
    public string grad { get; set; }
}

"FetchClient" from JSON

public static List<Klijent> DohvatiKlijente()
{
    List<Klijent> lKlijent = new List<Klijent>();
    StreamReader klijent = new StreamReader("x");
    string sJson = "";
    using (klijent)
    {
        sJson = klijent.ReadToEnd();
        lKlijent = JsonConvert.DeserializeObject<List<Klijent>>(sJson);
    }
    return lKlijent;
}

"AddClient" to JSON

OIB -> personal identificator
ID -> should go +1 with every entry of client
grad -> city
ime -> name
prezime -> surname

public static void DodavanjeKlijenata()
{

    Console.Write("Unesite OIB klijenta: ");
    string pOIB = Console.ReadLine();
    long nullOIB = 0;
    long.TryParse(pOIB, out nullOIB);
    int id = 0;
    Console.Write("Unesite ime klijenta: ");
    string ime1 = Console.ReadLine();
    Console.Write("Unesite prezime klijenta: ");
    string prezime1 = Console.ReadLine();
    Console.Write("Unesite grad klijenta: ");
    string grad1 = Console.ReadLine();
    List<Klijent> lKlijent = DohvatiKlijente();
    foreach (var Klijent in lKlijent)
    {
        id = Klijent.ID + 1;
    }
    Klijent dKlijent = new Klijent()
    {
        ID = id,
        OIB = nullOIB,
        ime = ime1,
        prezime = prezime1,
        grad = grad1
    };

        var serializer = new JsonSerializer();

        using (var sw = new StreamWriter("x"))
        using (JsonWriter writer = new JsonTextWriter(sw))
        {
            serializer.Serialize(writer, dKlijent);
        }
}

This code does work, but it seems to delete every time my JSON file and it's format is in one line only, I would like to have it in multiple lines.

Thank you :)

Answer 1

There are two things that you need to do here

Ensure new Client is appended to existing list

For this you can add the new client to the List

lKlijent.Add(dKlijent);

Now you need to serialize the List, instead of lKlijent

using (JsonWriter writer = new JsonTextWriter(sw))
{
    serializer.Serialize(writer, lKlijent);
}

Formatting

For formatting you can use Formatting Settings. For example,

var serializer = new JsonSerializer() { Formatting = Formatting.Indented} ;

Additional Comments

1. Calculation of ID

Instead of calculating the new ID using the following loop,

foreach (var Klijent in lKlijent)
{
        id = Klijent.ID + 1;
}

You could use Enumerable.Last() to get the last client in the list. For example,

var id = lKlijent?.Any()!=true? 0:lKlijent.Last().ID;

2. Rewriting DohvatiKlijente method

The DohvatiKlijente method could rewritten as

public static List<Klijent> DohvatiKlijente()
{
    return JsonConvert.DeserializeObject<List<Klijent>>(File.ReadAllText("C:\\Users\\Hrvoje\\Desktop\\Polica Osiguranja MAIN\\Polica Osiguranja\\klijent.json"));
}

Similarly, writing back to file can be simplified as

var jsonString = JsonConvert.SerializeObject(lKlijent,Newtonsoft.Json.Formatting.Indented);
File.WriteAllText(outputFilePath,jsonString);