export const metadata = {
    title: 'Entities',
    description:
        'Entities are simple JSON objects that represent the core data structures in Lysand.',
}

# Entities

Entities are the foundation of the Lysand protocol. A similar concept to entities are the [ActivityStreams](https://www.w3.org/TR/activitystreams-core/) objects, which are used to represent activities in the [ActivityPub](https://www.w3.org/TR/activitypub/) protocol. {{ className: 'lead' }}

## Entity Definition

An entity is a simple JSON object that represents a core data structure in Lysand. Entities are used to represent various types of data, such as users, notes, and more. Each entity has a unique `id` property that is used to identify it within the instance.

Any field in an entity not marked as `required` may be omitted or set to `null`.

<Row>
  <Col>

    <Properties>
        <Property name="id" type="string" required={true}>
            Unique identifier for the entity. Must be unique within the instance. Can be any string. Max of 512 UTF-8 characters.
        </Property>
        <Property name="type" type="string" required={true}>
            Type of the entity. Only types defined in the Lysand protocol are allowed. Use an [Extension](/extensions) if you want to define custom types.
        </Property>
        <Property name="created_at" type="ISO8601" required={true} typeLink="/types#iso-8601">
            Date and time when the entity was created. Must be an [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601) formatted string.

            <Note>
            Handling of dates that are valid but obviously incorrect (e.g. in the future) is left to the Implementation's discretion.
            </Note>
        </Property>
        <Property name="uri" type="URI" required={true} typeLink="/types#uri">
            URI of the entity. Should be unique and resolve to the entity. Must be an absolute URI.

            **Some entity types may not need a URI. This will be specified in the entity's documentation.**
        </Property>
        <Property name="extensions" type="Extensions" required={false} typeLink="/types#extensions">
            Extensions to the entity. Use this to add custom properties to the entity.

            Each custom property must be namespaced with the organization's reversed domain name, followed by the property name. Extensions should be used sparingly and only when necessary.
        </Property>
    </Properties>
  </Col>
  <Col sticky>

    ```jsonc {{ 'title': 'Example Entity' }}
    {
        "id": "9a8928b6-2526-4979-aab1-ef2f88cd5700",
        "type": "Delete",
        "created_at": "2022-01-01T12:00:00Z",
        "author": "https://bongo.social/users/63a00ab3-39b1-49eb-b88e-ed65d2361f3e",
        "deleted": "https://bongo.social/notes/54059ce2-9332-46fa-bf6a-598b5493b81b",
    }
    ``` 

    ```jsonc {{ 'title': 'With Extensions' }}
    {
        "id": "f0aacf0b-df7a-4ee5-a2ba-6c4acafd8642",
        "type": "Extension",
        "extension_type": "org.space:Zlorbs/Zlorb",
        "created_at": "2023-04-13T08:00:00Z",
        "uri": "https://space.org/zlorbs/f0aacf0b-df7a-4ee5-a2ba-6c4acafd8642",
        "extensions": { // [!code focus:100]
            "org.space:zlorbs": {
                "zlorb_type": "giant",
                "zlorb_size": "huge"
            },
            "org.lysand:location": {
                "latitude": 37.7749,
                "longitude": -122.4194
            }
        }
    }
    ```
    </Col>
</Row>

## Serialization

When serialized to a string, the JSON representation of an entity should follow the following rules:
- Keys must be sorted lexicographically.
- Should use UTF-8 encoding.
- Must be **signed** using the relevant [User](/entities/user)'s private key, or the [Server Actor](/entities/server-actor)'s private key if the entity is not associated with a particular user.
