REST framework includes support for customizable pagination styles. This allows you to modify how large result sets are split into individual pages of data.
The built-in styles currently all use links included as part of the content of the response. This style is more accessible when using the browsable API.
Pagination is only performed automatically if you're using the generic views or viewsets. If you're using a regular `APIView`, you'll need to call into the pagination API yourself to ensure you return a paginated response. See the source code for the `mixins.ListModelMixin` and `generics.GenericAPIView` classes for an example.
The default pagination style may be set globally, using the `DEFAULT_PAGINATION_CLASS` and `PAGE_SIZE` setting keys. For example, to use the built-in limit/offset pagination, you would do something like this:
You can also set the pagination class on an individual view by using the `pagination_class` attribute. Typically you'll want to use the same pagination style throughout your API, although you might want to vary individual aspects of the pagination, such as default or maximum page size, on a per-view basis.
If you want to modify particular aspects of the pagination style, you'll want to override one of the pagination classes, and set the attributes that you want to change.
*`page_size` - A numeric value indicating the page size. If set, this overrides the `PAGE_SIZE` setting. Defaults to the same value as the `PAGE_SIZE` settings key.
*`page_query_param` - A string value indicating the name of the query parameter to use for the pagination control.
*`page_size_query_param` - If set, this is a string value indicating the name of a query parameter that allows the client to set the page size on a per-request basis. Defaults to `None`, indicating that the client may not control the requested page size.
*`max_page_size` - If set, this is a numeric value indicating the maximum allowable requested page size. This attribute is only valid if `page_size_query_param` is also set.
*`last_page_strings` - A list or tuple of string values indicating values that may be used with the `page_query_param` to request the final page in the set. Defaults to `('last',)`
*`template` - The name of a template to use when rendering pagination controls in the browsable API. May be overridden to modify the rendering style, or set to `None` to disable HTML pagination controls completely. Defaults to `"rest_framework/pagination/numbers.html"`.
"offset" query parameter. The limit indicates the maximum number of items to return, and is equivalent to the `page_size` in other styles. The offset indicates the starting position of the query in relation to the complete set of unpaginated items.
**Request**:
GET https://api.example.org/accounts/?limit=100&offset=400
Optionally, you may also set a `PAGE_SIZE` key. If the `PAGE_SIZE` parameter is also used then the `limit` query parameter will be optional, and may be omitted by the client.
*`default_limit` - A numeric value indicating the limit to use if one is not provided by the client in a query parameter. Defaults to the same value as the `PAGE_SIZE` settings key.
*`limit_query_param` - A string value indicating the name of the "limit" query parameter. Defaults to `'limit'`.
*`offset_query_param` - A string value indicating the name of the "offset" query parameter. Defaults to `'offset'`.
*`max_limit` - If set this is a numeric value indicating the maximum allowable limit that may be requested by the client. Defaults to `None`.
*`template` - The name of a template to use when rendering pagination controls in the browsable API. May be overridden to modify the rendering style, or set to `None` to disable HTML pagination controls completely. Defaults to `"rest_framework/pagination/numbers.html"`.
The cursor-based pagination presents an opaque "cursor" indicator that the client may use to page through the result set. This pagination style only presents forward and reverse controls, and does not allow the client to navigate to arbitrary positions.
Cursor based pagination requires that there is a unique, unchanging ordering of items in the result set. This ordering might typically be a creation timestamp on the records, as this presents a consistent ordering to paginate against.
Cursor based pagination is more complex than other schemes. It also requires that the result set presents a fixed ordering, and does not allow the client to arbitrarily index into the result set. However it does provide the following benefits:
* Provides a consistent pagination view. When used properly `CursorPagination` ensures that the client will never see the same item twice when paging through records, even when new items are being inserted by other clients during the pagination process.
* Supports usage with very large datasets. With extremely large datasets pagination using offset-based pagination styles may become inefficient or unusable. Cursor based pagination schemes instead have fixed-time properties, and do not slow down as the dataset size increases.
Proper use of cursor based pagination requires a little attention to detail. You'll need to think about what ordering you want the scheme to be applied against. The default is to order by `"-created"`. This assumes that **there must be a 'created' timestamp field** on the model instances, and will present a "timeline" style paginated view, with the most recently added items first.
You can modify the ordering by overriding the `'ordering'` attribute on the pagination class, or by using the `OrderingFilter` filter class together with `CursorPagination`. When used with `OrderingFilter` you should strongly consider restricting the fields that the user may order by.
* Should be an unchanging value, such as a timestamp, slug, or other field that is only set once, on creation.
* Should be unique, or nearly unique. Millisecond precision timestamps are a good example. This implementation of cursor pagination uses a smart "position plus offset" style that allows it to properly support not-strictly-unique values as the ordering.
* Should be a non-nullable value that can be coerced to a string.
Using an ordering field that does not satisfy these constraints will generally still work, but you'll be losing some of the benefits of cursor pagination.
For more technical details on the implementation we use for cursor pagination, the ["Building cursors for the Disqus API"][disqus-cursor-api] blog post gives a good overview of the basic approach.
*`page_size` = A numeric value indicating the page size. If set, this overrides the `PAGE_SIZE` setting. Defaults to the same value as the `PAGE_SIZE` settings key.
*`ordering` = This should be a string, or list of strings, indicating the field against which the cursor based pagination will be applied. For example: `ordering = 'slug'`. Defaults to `-created`. This value may also be overridden by using `OrderingFilter` on the view.
*`template` = The name of a template to use when rendering pagination controls in the browsable API. May be overridden to modify the rendering style, or set to `None` to disable HTML pagination controls completely. Defaults to `"rest_framework/pagination/previous_and_next.html"`.
To create a custom pagination serializer class you should subclass `pagination.BasePagination` and override the `paginate_queryset(self, queryset, request, view=None)` and `get_paginated_response(self, data)` methods:
* The `paginate_queryset` method is passed the initial queryset and should return an iterable object that contains only the data in the requested page.
* The `get_paginated_response` method is passed the serialized page data and should return a `Response` instance.
Suppose we want to replace the default pagination output style with a modified format that includes the next and previous links under in a nested 'links' key. We could specify a custom pagination class like so:
class CustomPagination(pagination.PageNumberPagination):
def get_paginated_response(self, data):
return Response({
'links': {
'next': self.get_next_link(),
'previous': self.get_previous_link()
},
'count': self.page.paginator.count,
'results': data
})
We'd then need to setup the custom class in our configuration:
Note that if you care about how the ordering of keys is displayed in responses in the browsable API you might choose to use an `OrderedDict` when constructing the body of paginated responses, but this is optional.
Let's modify the built-in `PageNumberPagination` style, so that instead of include the pagination links in the body of the response, we'll instead include a `Link` header, in a [similar style to the GitHub API][github-link-pagination].
API responses for list endpoints will now include a `Link` header, instead of including the pagination links as part of the body of the response, for example:
---
![Link Header][link-header]
*A custom pagination style, using the 'Link' header'*
By default using the pagination classes will cause HTML pagination controls to be displayed in the browsable API. There are two built-in display styles. The `PageNumberPagination` and `LimitOffsetPagination` classes display a list of page numbers with previous and next controls. The `CursorPagination` class displays a simpler style that only displays a previous and next control.
Providing a template with either of these paths in a global template directory will override the default rendering for the relevant pagination classes.
Alternatively you can disable HTML pagination controls completely by subclassing on of the existing classes, setting `template = None` as an attribute on the class. You'll then need to configure your `DEFAULT_PAGINATION_CLASS` settings key to use your custom class as the default pagination style.
#### Low-level API
The low-level API for determining if a pagination class should display the controls or not is exposed as a `display_page_controls` attribute on the pagination instance. Custom pagination classes should be set to `True` in the `paginate_queryset` method if they require the HTML pagination controls to be displayed.
The `.to_html()` and `.get_html_context()` methods may also be overridden in a custom pagination class in order to further customize how the controls are rendered.
The following third party packages are also available.
## DRF-extensions
The [`DRF-extensions` package][drf-extensions] includes a [`PaginateByMaxMixin` mixin class][paginate-by-max-mixin] that allows your API clients to specify `?page_size=max` to obtain the maximum allowed page size.
