docs/object-serialization/csharp/basic-serialization.md

---
title: Basic Serialization
sidebar_position: 1
id: basic-serialization
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This page covers typed serialization APIs in the default xlang mode for Apache Fory™ C#.

## Object Graph Serialization

Use `[ForyStruct]` on your classes/structs and register them before use.

```csharp
using Apache.Fory;

[ForyStruct]
public sealed class Address
{
    public string Street { get; set; } = string.Empty;
    public int Zip { get; set; }
}

[ForyStruct]
public sealed class Person
{
    public long Id { get; set; }
    public string Name { get; set; } = string.Empty;
    public string? Nickname { get; set; }
    public List<int> Scores { get; set; } = [];
    public List<Address> Addresses { get; set; } = [];
}

Fory fory = Fory.Builder().Build();
fory.Register<Address>(100);
fory.Register<Person>(101);

Person person = new()
{
    Id = 42,
    Name = "Alice",
    Nickname = null,
    Scores = [10, 20, 30],
    Addresses = [new Address { Street = "Main", Zip = 94107 }],
};

byte[] payload = fory.Serialize(person);
Person decoded = fory.Deserialize<Person>(payload);
```

## Class Inheritance

An annotated class includes the supported members declared by its annotated
base classes in one flattened schema. Annotate every class in the hierarchy
directly; `[ForyStruct]` is not inherited.

```csharp
[ForyStruct]
public abstract class Entity
{
    [ForyField(1)]
    private long _id;

    public long Id => _id;
}

[ForyStruct]
public sealed class User : Entity
{
    [ForyField(2)]
    public string Name { get; set; } = string.Empty;
}
```

Public and assembly-accessible mutable members are included automatically.
Private, protected-only, and otherwise inaccessible fields or properties must
carry `[ForyField]` on the class that declares them. Abstract annotated bases
publish schema information for concrete descendants but are not registered or
serialized as roots.

The concrete derived type is still registered once:

```csharp
fory.Register<User>(102);
```

For a base class from an unmodifiable package, declare its fields explicitly as
described in [External Types](external-types.md).

## Typed API

### Serialize / Deserialize with byte arrays

```csharp
byte[] payload = fory.Serialize(value);
MyType decoded = fory.Deserialize<MyType>(payload);
```

### Deserialize from `ReadOnlySpan<byte>`

```csharp
ReadOnlySpan<byte> span = payload;
MyType decoded = fory.Deserialize<MyType>(span);
```

## Dynamic Payloads via Generic Object API

When the compile-time type is unknown or heterogeneous, use the generic API with `object?`.

```csharp
Dictionary<object, object?> value = new()
{
    ["k1"] = 7,
    [2] = "v2",
    [true] = null,
};

byte[] payload = fory.Serialize<object?>(value);
object? decoded = fory.Deserialize<object?>(payload);
```

Dynamic maps normally decode as `Dictionary<object, object?>` when they have no
null key. If the payload uses reference tracking for the dynamic map itself, C#
returns `NullableKeyDictionary<object, object?>` so nested references and null
keys point to the decoded map owner.

## Buffer Writer API

Serialize directly into `IBufferWriter<byte>` targets.

```csharp
using System.Buffers;

ArrayBufferWriter<byte> writer = new();
fory.Serialize(writer, value);

ArrayBufferWriter<byte> dynamicWriter = new();
fory.Serialize<object?>(dynamicWriter, value);
```

## Notes

- Reuse the same `Fory` or `ThreadSafeFory` instance for better performance.
- Primitive types and collections do not require user registration.
- Register user types handled by `[ForyStruct]`, `[ForyEnum]`, `[ForyUnion]`,
  external structural serializers, or custom serializers explicitly.

## Cross-Language Interoperability

The default xlang format is shared by all Fory runtimes. The following sections cover its cross-language type mapping, type identity, and interoperability requirements.

Apache Fory™ C# supports xlang serialization with other Fory implementations.

### Xlang Configuration

C# always writes and reads the xlang frame header. There is no mode switch, so interoperability code
only needs to configure the remaining settings such as compatibility mode and reference
tracking.

```csharp
Fory fory = Fory.Builder()
    .Build();
```

### Register with Stable IDs

```csharp
[ForyStruct]
public sealed class Person
{
    public string Name { get; set; } = string.Empty;
    public int Age { get; set; }
}

Fory fory = Fory.Builder()
    .Build();

fory.Register<Person>(100);
```

Use the same ID mapping on all languages.

Third-party classes, structs, and enums can use
[external-type serialization](external-types.md). Register the target type,
not its local serializer declaration, with the same ID or name used by the
other language peers.

### Register by Name

```csharp
fory.Register<Person>("com.example.Person");
```

### Xlang Example

#### C# (Serializer)

```csharp
Person person = new() { Name = "Alice", Age = 30 };
byte[] payload = fory.Serialize(person);
```

#### Java (Deserializer)

```java
Fory fory = Fory.builder()
        .withXlang(true)
        .withRefTracking(true)
    .build();

fory.register(Person.class, 100);
Person value = (Person) fory.deserialize(payloadFromCSharp);
```

#### Python (Deserializer)

```python
import pyfory

fory = pyfory.Fory(xlang=True, ref=True)
fory.register_type(Person, type_id=100)
value = fory.deserialize(payload_from_csharp)
```

### Type Mapping Reference

See [cross-language interoperability guide](../xlang.md) for complete mapping.

For reduced-precision numeric payloads, use `Half` / `Half[]` or `List<Half>` for xlang `float16`, and `BFloat16` / `BFloat16[]` or `List<BFloat16>` for xlang `bfloat16`.

### Lists and Dense Arrays

C# `List<T>` maps to Fory `list<T>`. Use the schema marker
`Apache.Fory.Schema.Types.Array<T>` when a field is dense `array<T>`.

| Fory schema       | C# schema marker sketch |
| ----------------- | ----------------------- |
| `list<int32>`     | `S.List<S.Int32>`       |
| `array<bool>`     | `S.Array<S.Bool>`       |
| `array<int8>`     | `S.Array<S.Int8>`       |
| `array<int16>`    | `S.Array<S.Int16>`      |
| `array<int32>`    | `S.Array<S.Int32>`      |
| `array<int64>`    | `S.Array<S.Int64>`      |
| `array<uint8>`    | `S.Array<S.UInt8>`      |
| `array<uint16>`   | `S.Array<S.UInt16>`     |
| `array<uint32>`   | `S.Array<S.UInt32>`     |
| `array<uint64>`   | `S.Array<S.UInt64>`     |
| `array<float16>`  | `S.Array<S.Float16>`    |
| `array<bfloat16>` | `S.Array<S.BFloat16>`   |
| `array<float32>`  | `S.Array<S.Float32>`    |
| `array<float64>`  | `S.Array<S.Float64>`    |

### Interoperability Best Practices

1. Keep type IDs stable and documented.
2. Keep compatible mode enabled for rolling upgrades.
3. Register all user types on both read/write peers.
4. Validate integration with real payload round trips.

### Related Guides

- [Type Registration](type-registration.md)
- [External Types](external-types.md)
- [Schema Evolution](schema-evolution.md)
- [Supported Types](supported-types.md)

## Related Topics

- [Type Registration](type-registration.md)
- [Supported Types](supported-types.md)
- [References](references.md)