How to insert new object in json file

Question

Follows json file:

[{"Id":0,"Nome":"","Endereco":""}]

Follows the class:

public class JsonResult
{
    public int Id { get; set; }
    public string Nome { get; set; }
    public string Endereco { get; set; }
}

Follows code:

string jsonToOutput = string.Empty;
using (StreamReader r = new StreamReader($@"{pathname}\file.json"))
{
    string json = r.ReadToEnd();
    var array = JArray.Parse(json);
    List<JsonResult> items = JsonConvert.DeserializeObject<List<JsonResult>>(json);

    var last = items[items.Count - 1].Id + 1;

    var itemToAdd = new JObject
    {
        ["Id"] = last,
        ["Nome"] = textBox_nome.Text,
        ["Endereco"] = textBox_endereco.Text
    };
    array.Add(itemToAdd);
    jsonToOutput = JsonConvert.SerializeObject(array, Formatting.None);
}

using (StreamWriter file = File.CreateText($@"{pathname}\file.json"))
{
    JsonSerializer serializer = new JsonSerializer();
    serializer.Serialize(file, jsonToOutput);
}

Result that I want:

[{"Id":0,"Nome":"","Endereco":""},{"Id":1,"Nome":"","Endereco":""}]

Final result:

"[{\"Id\":0,\"Nome\":\"\",\"Endereco\":\"\"},{\"Id\":1,\"Nome\":\"\",\"Endereco\":\"\"}]"

Second attempt:

string jsonToOutput = string.Empty;
using (StreamReader r = new StreamReader($@"{pathname}\file.json"))
{
    string json = r.ReadToEnd();
    List<JsonResult> items = JsonConvert.DeserializeObject<List<JsonResult>>(json);
    int last = items[items.Count - 1].Id + 1;
    List<JsonResult> _data = new List<JsonResult>
    {
        new JsonResult()
        {
            Id = last,
            Nome = "",
            Endereco = ""
        }
    };
    items.AddRange(_data);

    jsonToOutput = JsonConvert.SerializeObject(items);
}

using (StreamWriter file = File.CreateText($@"{pathname}\file.json"))
{
    JsonSerializer serializer = new JsonSerializer();
    serializer.Serialize(file, jsonToOutput);
}

Some solution ?

Answer 1

From what I understand you’re getting one json, playing in a list, adding a new item, converting again to json and saving.

For this just do the SerializeObject of the list,

string json = "[{\"Id\":0,\"Nome\":\"\",\"Endereco\":\"\"},{\"Id\":1,\"Nome\":\"\",\"Endereco\":\"\"}]";
List<JsonResult> items = JsonConvert.DeserializeObject<List<JsonResult>>(json);

var last = items[items.Count - 1].Id + 1;

items.Add(new JsonResult()
{
    Id = last,
    Nome = "Leonardo",
    Endereco = "Rua de baixo"
});

string myJsonOutput = JsonConvert.SerializeObject(items);

The variable myJsonOutput will generate a string json and so you can save that you will not "catch" the escapes

I also left in the .Netfiddle for reference

Answer 2

According to the comments (with the author’s response input), the error was that the object was being serialized twice.

So much here:

jsonToOutput = JsonConvert.SerializeObject(items);

How much here:

JsonSerializer serializer = new JsonSerializer();
serializer.Serialize(file, jsonToOutput);

The problem is that in the last line, it is Serializing an already serialized object. Soon the string formed in the second serialization is the first with the correct formatting all escaped (with a \" which prevents normal interpretation of quotation marks (")).

So, it’s time to write the serialized object.

File.WriteAllText($@"{pathname}\file.json", jsonToOutput);