Collection Types

Collections group multiple objects together.

Type Hierarchy

┌─────────────────────────────────────────┐
│              Collection                 │
├───────────────────┬─────────────────────┤
│  OrderedCollection │  CollectionPage    │
│                   │  OrderedCollectionPage│
└───────────────────┴─────────────────────┘

Collection

Unordered set of items.

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Collection",
  "id": "https://example.com/collection",
  "totalItems": 3,
  "items": [
    "https://example.com/item/1",
    "https://example.com/item/2",
    "https://example.com/item/3"
  ]
}

OrderedCollection

Items in specific order (newest first typically).

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "OrderedCollection",
  "id": "https://example.com/users/alice/outbox",
  "totalItems": 150,
  "first": "https://example.com/users/alice/outbox?page=true",
  "last": "https://example.com/users/alice/outbox?page=true&min_id=0"
}

CollectionPage

A page within a collection.

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "CollectionPage",
  "partOf": "https://example.com/collection",
  "items": ["..."],
  "next": "https://example.com/collection?page=2"
}

OrderedCollectionPage

A page with ordered items.

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "OrderedCollectionPage",
  "id": "https://example.com/users/alice/outbox?page=true",
  "partOf": "https://example.com/users/alice/outbox",
  "orderedItems": [
    { "type": "Create", "object": { "type": "Note" } }
  ],
  "next": "https://example.com/users/alice/outbox?page=2",
  "prev": "https://example.com/users/alice/outbox?page=0"
}

Properties

Property	Type	Description
totalItems	Integer	Total count
items	Array	Collection items
orderedItems	Array	Ordered items
first	URL	First page
last	URL	Last page
current	URL	Current page
next	URL	Next page
prev	URL	Previous page
partOf	URL	Parent collection

Common Uses

Collection	Type	Purpose
inbox	OrderedCollection	Received activities
outbox	OrderedCollection	Published activities
followers	OrderedCollection	Follower list
following	OrderedCollection	Following list
liked	OrderedCollection	Liked objects
shares	Collection	Boost/announce list
replies	Collection	Comment thread

Pagination Pattern

┌─────────────────────────────────────────────────────┐
│ OrderedCollection (root)                            │
│ totalItems: 500                                     │
│ first: /outbox?page=true ──────┐                    │
└────────────────────────────────│────────────────────┘
                                 ▼
┌─────────────────────────────────────────────────────┐
│ OrderedCollectionPage (page 1)                      │
│ orderedItems: [20 items]                            │
│ next: /outbox?page=2 ──────────┐                    │
└────────────────────────────────│────────────────────┘
                                 ▼
┌─────────────────────────────────────────────────────┐
│ OrderedCollectionPage (page 2)                      │
│ orderedItems: [20 items]                            │
│ next: /outbox?page=3                                │
└─────────────────────────────────────────────────────┘

Implementation

app.get('/users/:user/outbox', async (req, res) => {
  const page = req.query.page;
  const user = req.params.user;

  if (!page) {
    // Return collection summary
    const count = await getActivityCount(user);
    return res.json({
      "@context": "https://www.w3.org/ns/activitystreams",
      "type": "OrderedCollection",
      "id": `https://example.com/users/${user}/outbox`,
      "totalItems": count,
      "first": `https://example.com/users/${user}/outbox?page=true`
    });
  }

  // Return paginated items
  const activities = await getActivities(user, page);
  res.json({
    "@context": "https://www.w3.org/ns/activitystreams",
    "type": "OrderedCollectionPage",
    "partOf": `https://example.com/users/${user}/outbox`,
    "orderedItems": activities,
    "next": `https://example.com/users/${user}/outbox?page=${page + 1}`
  });
});

See Also

• Followers & Following
• Outbox Endpoint