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Pagination

Adds a links object to packages, to support pagination.

Links

The top-level links object in release packages and record packages has three fields:

  • next: A URL to the next sequential package
  • prev: A URL to the previous sequential package

To construct the next and/or prev URLs, it is encouraged to use query string parameters like:

  • since=TIMESTAMP, to return a page of results that are modified after the since timestamp, in chronological order
  • offset=NUMBER, to return a page of results that are positioned after the offset number, in sequential order (for example, if the results are retrieved from a SQL database)

It is discouraged to use page=NUMBER with results ordered in reverse chronology, because:

  • A given page won't return the same results over time. page=1 will return different results today, next week, and next year.
  • Users can receive duplicate results while paginating. For example, if a new release is published to page 1 while users are paginating, then the result at the bottom of each page will be moved to the top of the following page.
  • It is harder for users to synchronize with the API. With since or offset, users can retrieve new results by submitting the timestamp or offset of their last request. With page, users need to determine which results are new or old.

Reference: HTML link types, 18F API Standards, Government of Canada Standards on APIs, Government of Ontario API Guidelines, OpenActive Realtime Paged Data Exchange.

Example

A publisher has a large number of releases. Instead of gathering them into one release package, it segments them into multiple release packages, via an API with pagination. The links.next field provides the link to the next page.

{
  "uri": "https://standard.open-contracting.org/examples/releases/ocds-213czf-000-00001-05-contract.json",
  "license": "http://opendatacommons.org/licenses/pddl/1.0/",
  "publicationPolicy": "https://github.com/open-contracting/sample-data/",
  "version": "1.1",
  "releases": [
    {
      "ocid": "ocds-213czf-000-00001",
      "id": "ocds-213czf-000-00001-05-contract",
      "date": "2010-05-10T10:30:00Z",
      "language": "en",
      "tag": [
        "contract"
      ],
      "initiationType": "tender"
    }
  ],
  "links": {
    "next": "https://raw.githubusercontent.com/open-contracting/api-specification/master/multiple-file-api-next/releases-2015.json"
  }
}

Issues

Report issues for this extension in the ocds-extensions repository, putting the extension's name in the issue's title.

Changelog

2020-11-05

  • Remove links.all.
  • Remove packageMetadata.

2020-04-24

  • Add minProperties, minItems and/or minLength properties.

2020-04-15

  • Deprecate links.all.
  • Deprecate packageMetadata.