ReferenceHandler.Preserve Property

Definition

Namespace:

System.Text.Json.Serialization

Assembly:

System.Text.Json.dll

Source:

ReferenceHandler.cs

Gets an object that indicates whether metadata properties are honored when JSON objects and arrays are deserialized into reference types, and written when reference types are serialized. This is necessary to create round-trippable JSON from objects that contain cycles or duplicate references.

public:
 static property System::Text::Json::Serialization::ReferenceHandler ^ Preserve { System::Text::Json::Serialization::ReferenceHandler ^ get(); };

public static System.Text.Json.Serialization.ReferenceHandler Preserve { get; }

static member Preserve : System.Text.Json.Serialization.ReferenceHandler

Public Shared ReadOnly Property Preserve As ReferenceHandler

Property Value

ReferenceHandler

Remarks

• On Serialize:

  • When writing complex reference types, the serializer also writes metadata properties ($id, $values, and $ref) within them.
  • The output JSON will contain an extra $id property for every object, and for every enumerable type the JSON array emitted will be nested within a JSON object containing an $id and $values property.
  • ReferenceEquals(Object, Object) is used to determine whether objects are identical.
  • When an object is identical to a previously serialized one, a pointer ($ref) to the identifier ($id) of such object is written instead.
  • No metadata properties are written for value types.

• On Deserialize:

  • The metadata properties within the JSON that are used to preserve duplicated references and cycles will be honored as long as they are well-formed.*
  • For JSON objects that don't contain any metadata properties, the deserialization behavior is identical to not using Preserve.
  • For value types, the $id metadata property is ignored. A JsonException is thrown if a $ref metadata property is found within the JSON object.
  • For enumerable value types, the $values metadata property is ignored.

• For the metadata properties within the JSON to be considered well-formed, they must follow these rules:

  • Unless AllowOutOfOrderMetadataProperties is set to true, the $id metadata property must be the first property in the JSON object.
  • A JSON object that contains a $ref metadata property must not contain any other properties.
  • The value of the $ref metadata property must refer to an $id that has appeared earlier in the JSON.
  • The value of the $id and $ref metadata properties must be a JSON string.
  • For enumerable types, such as List<T>, the JSON array must be nested within a JSON object containing an $id and $values metadata property, in that order. (However, the order is not important if AllowOutOfOrderMetadataProperties is set to true.)
  • For enumerable types, the $values metadata property must be a JSON array.
  • The $values metadata property is only valid when referring to enumerable types.

If the JSON is not well-formed, a JsonException is thrown.