How to use string.Format with curly brackets

How to use string.Format with curly brackets

Problem Description:

I want to create a json string that contains a list of long values with the following structure:

I solved the problem with the line below, but I feel like I could do it with a cleaner command(string.Format).

var json = "{"document_ids":" + JsonConvert.SerializeObject(My List<long>) + "}";

But the command I write with string.Format gives an error message.

var json = string.Format("{"document_ids":{0}}", JsonConvert.SerializeObject(My List<long>));

I get this error message.
System.FormatException: ‘Input string was not in a correct format.’

Solution – 1

Do not manually assemble json strings. There are already useful classes that make the most work for you. Just use the System.Text.Json.JsonSerializer class for example.

A full working example would be this:

internal class Program
    static void Main( string[] args )
        var myData = new MyData()
            MyListOfLongs = new List<long>() { 23461504, 20639162, 20395579 }

        var jsonString = JsonSerializer.Serialize( myData, new JsonSerializerOptions() { WriteIndented = true } );

public class MyData
    [JsonPropertyName( "document_ids" )]
    public List<long> MyListOfLongs
    { get; set; }

The variable jsonString contains your desired json string ^^

If you like to deserialize the string again, take a look at the class System.Text.Json.JsonSerializer again … it contains also a Deserialize method.

Solution – 2

You can serialize an anonymous object having such a document_ids property.

var numbers = new List<long> { 23461504, 20639162, 20395579 };

var json = JsonConvert.SerializeObject(
        document_ids = numbers
Rate this post
We use cookies in order to give you the best possible experience on our website. By continuing to use this site, you agree to our use of cookies.