Supported types in System.Text.Json

This article gives an overview of which types are supported for serialization and deserialization.

Types that serialize as JSON objects

The following types serialize as JSON objects:

• Classes^*
• Structs
• Interfaces
• Records and struct records

* Non-dictionary types that implement IEnumerable<T> serialize as JSON arrays. Dictionary types, which do implement IEnumerable<T>, serialize as JSON objects.

The following code snippet shows the serialization of a simple struct.

public static void Main()
{
    var coordinates = new Coords(1.0, 2.0);
    string json = JsonSerializer.Serialize(coordinates);
    Console.WriteLine(json);

    // Output:
    // {"X":1,"Y":2}
}

public readonly struct Coords
{
    public Coords(double x, double y)
    {
        X = x;
        Y = y;
    }

    public double X { get; }
    public double Y { get; }
}

Types that serialize as JSON arrays

.NET collection types serialize as JSON arrays. System.Text.Json.JsonSerializer supports a collection type for serialization if it:

• Derives from IEnumerable or IAsyncEnumerable<T>.
• Contains elements that are serializable.

The serializer calls the GetEnumerator() method and writes the elements.

Deserialization is more complicated and is not supported for some collection types.

The following sections are organized by namespace and show which types are supported for serialization and deserialization.

• System.Array namespace
• System.Collections namespace
• System.Collections.Generic namespace
• System.Collections.Immutable namespace
• System.Collections.Specialized namespace
• System.Collections.Concurrent namespace
• System.Collections.ObjectModel namespace
• Custom collections

System.Array namespace

System.Collections namespace

* See Support round trip for Stack types.

System.Collections.Generic namespace

* See Supported key types.

† See the following section on IAsyncEnumerable<T>.

‡ See Support round trip for Stack types.

IAsyncEnumerable<T>

The following examples use streams as a representation of any async source of data. The source could be files on a local machine, or results from a database query or web service API call.

Stream serialization

System.Text.Json supports serializing IAsyncEnumerable<T> values as JSON arrays, as shown in the following example:

using System.Text.Json;

namespace IAsyncEnumerableSerialize;

public class Program
{
    public static async Task Main()
    {
        using Stream stream = Console.OpenStandardOutput();
        var data = new { Data = PrintNumbers(3) };
        await JsonSerializer.SerializeAsync(stream, data);
    }

    static async IAsyncEnumerable<int> PrintNumbers(int n)
    {
        for (int i = 0; i < n; i++)
        {
            await Task.Delay(1000);
            yield return i;
        }
    }
}
// output:
//  {"Data":[0,1,2]}

IAsyncEnumerable<T> values are only supported by the asynchronous serialization methods, such as JsonSerializer.SerializeAsync.

Stream deserialization

The DeserializeAsyncEnumerable method supports streaming deserialization, as shown in the following example:

using System.Text;
using System.Text.Json;

namespace IAsyncEnumerableDeserialize;

public class Program
{
    public static async Task Main()
    {
        using var stream = new MemoryStream(Encoding.UTF8.GetBytes("[0,1,2,3,4]"));
        await foreach (int item in JsonSerializer.DeserializeAsyncEnumerable<int>(stream))
        {
            Console.WriteLine(item);
        }
    }
}
// output:
//0
//1
//2
//3
//4

The DeserializeAsyncEnumerable method only supports reading from root-level JSON arrays.

The DeserializeAsync method supports IAsyncEnumerable<T>, but its signature doesn't allow streaming. It returns the final result as a single value, as shown in the following example.

using System.Text;
using System.Text.Json;

namespace IAsyncEnumerableDeserializeNonStreaming;

public class MyPoco
{
    public IAsyncEnumerable<int>? Data { get; set; }
}

public class Program
{
    public static async Task Main()
    {
        using var stream = new MemoryStream(Encoding.UTF8.GetBytes(@"{""Data"":[0,1,2,3,4]}"));
        MyPoco? result = await JsonSerializer.DeserializeAsync<MyPoco>(stream)!;
        await foreach (int item in result!.Data!)
        {
            Console.WriteLine(item);
        }
    }
}
// output:
//0
//1
//2
//3
//4

In this example, the deserializer buffers all IAsyncEnumerable<T> contents in memory before returning the deserialized object. This behavior is necessary because the deserializer needs to read the entire JSON payload before returning a result.

System.Collections.Immutable namespace

* See Support round trip for Stack types.

† See Supported key types.

System.Collections.Specialized namespace

* When BitVector32 is deserialized, the Data property is skipped because it doesn't have a public setter. No exception is thrown.

System.Collections.Concurrent namespace

* See Support round trip for Stack types.

† See Supported key types.

System.Collections.ObjectModel namespace

* Non-string keys are not supported.

Custom collections

Any collection type that isn't in one of the preceding namespaces is considered a custom collection. Such types include user-defined types and types defined by ASP.NET Core. For example, Microsoft.Extensions.Primitives is in this group.

All custom collections (everything that derives from IEnumerable) are supported for serialization, as long as their element types are supported.

Deserialization support

A custom collection is supported for deserialization if it:

• Isn't an interface or abstract.

• Has a parameterless constructor.

• Contains element types that are supported by JsonSerializer.

• Implements or inherits one or more of the following interfaces or classes:

  • ConcurrentQueue<T>
  • ConcurrentStack<T> *
  • ICollection<T>
  • IDictionary
  • IDictionary<TKey,TValue> †
  • IList
  • IList<T>
  • Queue
  • Queue<T>
  • Stack *
  • Stack<T> *

  * See Support round trip for Stack types.

  † See Supported key types.

Known issues

There are known issues with the following custom collections:

• ExpandoObject: See dotnet/runtime#29690.
• DynamicObject: See dotnet/runtime#1808.
• DataTable: See dotnet/docs#21366.
• Microsoft.AspNetCore.Http.FormFile: See dotnet/runtime#1559.
• Microsoft.AspNetCore.Http.IFormCollection: See dotnet/runtime#1559.

For more information about known issues, see the open issues in System.Text.Json.

Supported key types

When used as the keys of Dictionary and SortedList types, the following types have built-in support:

• Boolean
• Byte
• DateTime
• DateTimeOffset
• Decimal
• Double
• Enum
• Guid
• Int16
• Int32
• Int64
• Object (Only on serialization and if the runtime type is one of the supported types in this list.)
• SByte
• Single
• String
• TimeSpan
• UInt16
• UInt32
• UInt64
• Uri
• Version

In addition, the JsonConverter<T>.WriteAsPropertyName(Utf8JsonWriter, T, JsonSerializerOptions) and JsonConverter<T>.ReadAsPropertyName(Utf8JsonReader, Type, JsonSerializerOptions) methods let you add dictionary key support for any type of your choosing.

Unsupported types

The following types aren't supported for serialization:

• System.Type and System.Reflection.MemberInfo
• ReadOnlySpan<T>, Span<T>, and ref structs in general
• Delegate types
• IntPtr and UIntPtr

System.Data namespace

There are no built-in converters for DataSet, DataTable, and related types in the System.Data namespace. Deserializing these types from untrusted input is not safe, as explained in the security guidance. However, you can write a custom converter to support these types. For sample custom converter code that serializes and deserializes a DataTable, see RoundtripDataTable.cs.

See also

• Populate initialized properties
• System.Text.Json overview
• System.Text.Json API reference
• System.Text.Json.Serialization API reference