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

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!

For the record, your Person class has properties in Sentence case. Pascal case would be FirstName and LastName — user1007074
– user1007074, Commented May 17, 2022 at 14:00
I got this behavior by default in .net 6. Trying to get rid of it :D — Anil P Babu
– Anil P Babu, Commented Feb 9, 2023 at 18:54

Kahbazi · Accepted Answer · 2019-10-20 19:55:21Z

158

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);

answered Oct 20, 2019 at 19:55

Kahbazi

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7 Comments

Alexander Staroselsky Over a year ago

There is no way to specify serialization options for the entire project/application with System.Text.Json? This was trivial before System.Text.Json

Kahbazi Over a year ago

I don't think so. You need to pass the settings

dbc Over a year ago

@AlexanderStaroselsky - no, see Is There A Way To Globally Set Default Options For System.Text.Json.JsonSerializer?.

Liam Over a year ago

This is possible with Json.Net

Sujoy Over a year ago

JsonSerializer does not contain property called Parse ???

|

Piotr Kula · Accepted Answer · 2020-05-12 20:20:13Z

69

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;
        );

edited May 12, 2020 at 20:20

Piotr Kula

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answered Jan 24, 2020 at 7:31

Ramil Aliyev 007

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1 Comment

Ted Over a year ago

Setting PropertyNamingPolicy to null resolved it. I first tried removing the line altogether (it was camelCase before), but that does not work - you need to set it to null =)

sutherlandahoy · Accepted Answer · 2021-03-09 10:49:38Z

57

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.

edited Mar 9, 2021 at 10:49

answered Dec 3, 2019 at 18:37

sutherlandahoy

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1 Comment

Mark Lazarides Over a year ago

This worked for me. FTR, I didn't have .AddMvc() in my services before this, only adding it so AddJsonOptions could be added. All my server-client serialisation issues went away.....

haldo · Accepted Answer · 2021-03-05 10:38:01Z

24

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.

The below will configure System.Text.Json for Json passed through a controller endpoint:

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

edited Mar 5, 2021 at 10:38

answered Oct 20, 2019 at 19:56

haldo

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2 Comments

Piotr Kula Over a year ago

FYI: PropertyNameCaseInsensitive is only for incoming JSON. ` options.JsonSerializerOptions.PropertyNamingPolicy= null;` will serialise outgoing JSON PascalCase

PillowMetal Over a year ago

What @PiotrKula says is true... PropertyNameCaseInsensitive is only used on incoming JSON payloads, but in addition to PropertyNamingPolicy dictating the rules on outgoing JSON payload creation during serialization, it ALSO expects that incoming payloads will mach the policy on deserialization; if it does not, your deserialization class members will have default values - this where PropertyNameCaseInsensitive fills the gap, it will allow deserialization to succeed regardless the incoming payload casing.

Dave · Accepted Answer · 2022-11-17 01:49:38Z

14

.NET Core 7 Minimal API solution

To prevent pascal case properties from being renamed to camel case during serialization, use the ConfigureHttpJsonOptions method of the builder's service property.

builder.Services.ConfigureHttpJsonOptions(options => options.SerializerOptions.PropertyNamingPolicy = null);

To force conversion to camel case (default behavior), use:

builder.Services.ConfigureHttpJsonOptions(options => options.SerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase);

answered Nov 17, 2022 at 1:49

Dave

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1 Comment

Sam Over a year ago

Thanks for your answer. I could not get a TrimStringConverter to fire when using builder.AddRazorPages().AddJsonOptions(options => options...). Custom converters added to that method do not fire during model binding in minimal apis. However, it does appear that converters specified in ConfigureHttpJsonOptions do run.

Ramil Aliyev 007 · Accepted Answer · 2021-07-22 06:45:32Z

13

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?

edited Jul 22, 2021 at 6:45

Ramil Aliyev 007

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answered Nov 18, 2019 at 16:39

Pierre-Paul St-Pierre

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Comments

Mazz Ebra · Accepted Answer · 2021-08-24 17:49:03Z

3

Try this!

In StartUp.cs inside the ConfigureServices method write:

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

You need namespaces such as Newtonsoft.Json.Serialization & System.Text.Json

edited Aug 24, 2021 at 17:49

answered Aug 19, 2021 at 19:34

Mazz Ebra

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2 Comments

Mark Schultheiss Over a year ago

This would be better if you document where this should go AND how this differs from similar answers, how would we know you did not just copy those?

Mazz Ebra Over a year ago

@MarkSchultheiss I have done that now. Thanks for feed back.

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