https://github.com/freckle/yesod-page-cursor
Cursor based pagination for yesod
https://github.com/freckle/yesod-page-cursor
Last synced: 8 months ago
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Cursor based pagination for yesod
- Host: GitHub
- URL: https://github.com/freckle/yesod-page-cursor
- Owner: freckle
- License: mit
- Created: 2019-04-14T19:16:02.000Z (about 7 years ago)
- Default Branch: main
- Last Pushed: 2023-06-27T15:45:37.000Z (almost 3 years ago)
- Last Synced: 2024-04-25T23:31:23.269Z (about 2 years ago)
- Language: Haskell
- Size: 91.8 KB
- Stars: 1
- Watchers: 22
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.lhs
- Changelog: ChangeLog.md
- License: LICENSE
Awesome Lists containing this project
README
# yesod-page-cursor
[](https://hackage.haskell.org/package/yesod-page-cursor)
[](http://stackage.org/nightly/package/yesod-page-cursor)
[](http://stackage.org/lts/package/yesod-page-cursor)
[](https://github.com/freckle/yesod-page-cursor/actions/workflows/ci.yml)
Cursor based pagination for `yesod` using index friendly keyset cursors.
Primer: [No Offset](https://use-the-index-luke.com/no-offset)
```haskell
mkPersist sqlSettings [persistLowerCase|
SomeAssignment json
createdAt UTCTime
teacherId Int
courseId Int
|]
getSomeR :: Handler Value
getSomeR = do
teacherId <- requiredParam "teacherId"
mCourseId <- optionalParam "courseId"
page <- withPageAbsolute 100 entityKey $ \Cursor {..} -> do
fmap (sort cursorPosition) . runDB $ selectList
(catMaybes
[ Just $ SomeAssignmentTeacherId ==. teacherId
, (SomeAssignmentCourseId ==.) <$> mCourseId
, whereClause cursorPosition
]
)
[LimitTo $ unLimit cursorLimit, orderBy cursorPosition]
returnJson $ keyValueEntityToJSON <$> page
where
whereClause = \case
First -> Nothing
Previous p -> Just $ persistIdField <. p
Next p -> Just $ persistIdField >. p
Last -> Nothing
orderBy = \case
First -> Asc persistIdField
Previous _ -> Desc persistIdField
Next _ -> Asc persistIdField
Last -> Desc persistIdField
sort = \case
First -> id
Previous _ -> reverse
Next _ -> id
Last -> reverse
```
`cursorLastPosition` is configurable. A page sorted by `created_at` may look
like:
```haskell
getSortedSomeR :: Handler Value
getSortedSomeR = do
page <- withPageAbsolute 100 (someAssignmentCreatedAt . entityVal)
$ \Cursor {..} -> do
fmap (sort cursorPosition) . runDB $ selectList
(whereClause cursorPosition)
[ LimitTo $ unLimit cursorLimit
, orderBy cursorPosition
]
returnJson $ keyValueEntityToJSON <$> page
where
whereClause = \case
First -> []
Previous createdAt ->
[ SomeAssignmentCreatedAt <=. createdAt
]
Next createdAt ->
[ SomeAssignmentCreatedAt >=. createdAt
]
Last -> []
orderBy = \case
First -> Asc SomeAssignmentCreatedAt
Previous _ -> Desc SomeAssignmentCreatedAt
Next _ -> Asc SomeAssignmentCreatedAt
Last -> Desc SomeAssignmentCreatedAt
sort = \case
First -> id
Previous _ -> reverse
Next _ -> id
Last -> reverse
```
## Usage
Paginated requests return a single page and a link with a cursor token to
retrieve the next page.
```console
% curl 'some-rest.com/endpoint?limit=3'
{
"first": : "https://some-rest.com/endpoint?next=eyJsYXN0UG9zaXRpb24iOjMsInBhcmFtcyI6WzEsbnVsbF0sImxpbWl0IjozfQ==",
"previous": null,
"next": "https://some-rest.com/endpoint?next=eyJsYXN0UG9zaXRpb24iOjMsInBhcmFtcyI6WzEsbnVsbF0sImxpbWl0IjozfQ==",
"data": [...]
}
```
The link can be used to retrieve the next page.
```console
% curl 'some-rest.com/endpoint?next=eyJsYXN0UG9zaXRpb24iOjMsInBhcmFtcyI6WzEsbnVsbF0sImxpbWl0IjozfQ=='
{
"first": : "https://some-rest.com/endpoint?next=eyJsYXN0UG9zaXRpb24iOjMsInBhcmFtcyI6WzEsbnVsbF0sImxpbWl0IjozfQ==",
"previous": "https://some-rest.com/endpoint?next=eyJsYXN0UG9zaXRpb24iOjMsInBhcmFtcyI6WzEsbnVsbF0sImxpbWl0IjozfQ==",
"next": "https://some-rest.com/endpoint?next=eyJsYXN0UG9zaXRpb24iOjMsInBhcmFtcyI6WzEsbnVsbF0sImxpbWl0IjozfQ==",
"data": [...]
}
```
If no pages remain then no link is returned
```console
% curl 'some-rest.com/endpoint?next=eyJsYXN0UG9zaXRpb24iOjMsInBhcmFtcyI6WzEsbnVsbF0sImxpbWl0IjozfQ=='
{
"first": : "https://some-rest.com/endpoint?next=eyJsYXN0UG9zaXRpb24iOjMsInBhcmFtcyI6WzEsbnVsbF0sImxpbWl0IjozfQ==",
"previous": "https://some-rest.com/endpoint?next=eyJsYXN0UG9zaXRpb24iOjMsInBhcmFtcyI6WzEsbnVsbF0sImxpbWl0IjozfQ==",
"next": null,
"data": [...]
}
```