JSON object contains a trailing comma at the end which is not supported

When you try to deserialize JSON that includes an extra comma at the end, you may encounter the following error:

The JSON object contains a trailing comma at the end which is not supported in this mode. Change the reader options.

In JSON, properties are separated by commas, and an extra comma occurs when a property is followed by a comma but no subsequent property exists.

Here's an example showing an extra comma:

{
    "id": 101,
    "name": "The Matrix",
}

This is technically invalid JSON (based on the official JSON specification), but deserialization should ideally handle this more gracefully. You can adjust the serializer to allow extra commas.

Solution

To allow extra commas, you can set the JsonSerializerOptions.AllowTrailingCommas to true, like so:

using System.Text.Json;

var movieJson = "{\"id\":101,\"name\":\"The Matrix\",}";

var options = new JsonSerializerOptions()
{
    AllowTrailingCommas = true
};

var movie = JsonSerializer.Deserialize<Movie>(movieJson, options);

In this example:

• AllowTrailingCommas = true: This setting in the JsonSerializerOptions allows the deserialization process to handle JSON with a trailing comma without throwing an error.
• The JsonSerializer.Deserialize method then works with the movieJson string, even if it has an extra comma at the end.

If you're working within an ASP.NET Core application, you can modify the global JSON serialization settings to allow trailing commas. To do this, update the Startup.cs file or wherever you configure services for the application.

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers().AddJsonOptions(options =>
    {
        options.JsonSerializerOptions.AllowTrailingCommas = true;
    });
}

This allows all JSON deserialization in your ASP.NET Core application to accept trailing commas.