ASP.NET Core 3.0 System.Text.Json Camel Case Seria

Question

In ASP.NET Core 3.0 Web API project, how do you specify System.Text.Json serialization options to serialize/deserialize Pascal Case properties to Camel Case and vice versa automatically?

Given a model with Pascal Case properties such as:

public class Person
{
    public string Firstname { get; set; }
    public string Lastname { get; set; }
}

And code to use System.Text.Json to deserialize a JSON string to type of Person class:

var json = "{\"firstname\":\"John\",\"lastname\":\"Smith\"}";
var person = JsonSerializer.Deserialize<Person>(json);

Does not successfully deserialize unless JsonPropertyName is used with each property like:

public class Person
{
    [JsonPropertyName("firstname")
    public string Firstname { get; set; }
    [JsonPropertyName("lastname")
    public string Lastname { get; set; }
}

I tried the following in startup.cs, but it did not help in terms of still needing JsonPropertyName:

services.AddMvc().AddJsonOptions(options =>
{
    options.JsonSerializerOptions.DictionaryKeyPolicy = JsonNamingPolicy.CamelCase;
    options.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
});

// also the following given it's a Web API project

services.AddControllers().AddJsonOptions(options => {
    options.JsonSerializerOptions.DictionaryKeyPolicy = JsonNamingPolicy.CamelCase;
    options.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
        });

How can you set Camel Case serialize/deserialize in ASP.NET Core 3.0 using the new System.Text.Json namespace?

Thanks!

Answer 1

In startup.cs:

// keeps the casing to that of the model when serializing to json (default is converting to camelCase)
services.AddMvc()
    .AddJsonOptions(options => options.JsonSerializerOptions.PropertyNamingPolicy = null); 

This means you don't need to import newtonsoft.json.

The only other option for options.JsonSerializerOptions.PropertyNamingPolicy is JsonNamingPolicy.CamelCase. There do not seem to be any other JsonNamingPolicy naming policy options, such as snake_case or PascalCase.

Answer 2

You can use PropertyNameCaseInsensitive. You need to pass it as a parameter to the deserializer.

var json = "{\"firstname\":\"John\",\"lastname\":\"Smith\"}";
var options = new JsonSerializerOptions() { PropertyNameCaseInsensitive = true };
var person = JsonSerializer.Deserialize<Person>(json, options);

which (from the docs):

Gets or sets a value that determines whether a property's name uses a case-insensitive comparison during deserialization. The default value is false

So, it doesn't specify camelCase or PascalCase but it will use case-insensitive comparison. Not sure if this meets your requirements.

---

Note: I wasn't able to set this application wide. The below does not work after testing:

services.AddControllers()
        .AddJsonOptions(options => {
            options.JsonSerializerOptions.PropertyNameCaseInsensitive = true;
         }); 

Answer 3

If you want CamelCase serialization use this code in Startup.cs: (for example firstName)

        services.AddControllers()
                .AddJsonOptions(options =>
                {
                    options.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
                });

If you want PascalCase serialization use this code in Startup.cs: (for example FirstName)

 services.AddControllers()
         .AddJsonOptions(options =>
         {
                    options.JsonSerializerOptions.PropertyNamingPolicy= null;
         });

Answer 4

AddJsonOptions() would config System.Text.Json only for MVC. If you want to use JsonSerializer in your own code you should pass the config to it.

var options = new JsonSerializerOptions
{
    PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
};

var json = "{\"firstname\":\"John\",\"lastname\":\"Smith\"}";
var person = JsonSerializer.Parse<Person>(json, options);

Answer 5

You can still set it application wide by installing Microsoft.AspNetCore.Mvc.NewtonsoftJson Nuget Package, which allows you to use the previous Json serializer implementation :

services.AddControllers()
        .AddNewtonsoftJson(options =>
        {
            options.SerializerSettings.ContractResolver = new DefaultContractResolver();
        });

Credits to Poke, answer found here : Where did IMvcBuilder AddJsonOptions go in .Net Core 3.0?