CursorPagination

CursorPagination is a library for Vapor’s Fluent that allows you to paginate queries using an opaque cursor. If you are looking for offset based pagination for Fluent, check out Pagination. If you’re not sure what cursor pagination is, or whether you need cursor or offset pagination, I recommend this great writeup from the Slack team explaining the difference between the two, and the pros and cons of each.

Installation

CursorPagination is available through Swift Package Manager. To install, add the following to your Package.swift file.

let package = Package(
    name: "YourProject",
    dependencies: [
        ...
        .package(url: "https://github.com/Appsaurus/CursorPagination", from: "0.1.0"),
    ],
    targets: [
      .target(name: "YourApp", dependencies: ["CursorPagination", ... ])
    ]
)
        

Usage

Check the app included in this project for a complete example. Here are some of the basics:

1. Import the library

import CusorPagination

2. Extend your model class to adopt CusorPaginatable protocol

You can simply declare the protocol adoption and inherit the default implementations.

extension KitchenSink: CursorPaginatable{}

Or you can set some default configurations by implementing any of the following static class vars.

extension KitchenSink: CursorPaginatable{
    public static var defaultPageSorts: [CursorSort<KitchenSink>] {
        return [idKey.descendingSort]
    }
    public static var defaultPageSize: Int {
        return 20
    }

    public static var maxPageSize: Int? {
        return 50
    }
}

3. Setup your routes

Setup routes to return a Future<CursorPage<YourModel>>. When you run your query, simply call paginate(request: sorts: ) on your class or on a QueryBuilder.

router.get("modelsByDate") { request -> Future<CursorPage<KitchenSink>> in
    return try KitchenSink.paginate(database: Database,
                     sorts: .descending(\.dateField))
}

On your first request, omitting a cursor tells the method that you are starting at the first page.

curl "http://localhost:8080/modelsByDate?limit=5"

Results in:

{  
   "remaining":45,
   "data":[  
      {  
         "booleanField":false,
         "id":10,
         "stringField":"Hammes Glen",
         "doubleField":718.52944714909995,
         "dateField":"2102-06-07T12:58:40Z",
         "intField":82
      },
      {  
         "booleanField":false,
         "id":11,
         "stringField":"Stracke Green",
         "doubleField":808.52215080719998,
         "dateField":"2094-08-08T15:32:25Z",
         "intField":714
      },
      {  
         "intField":789,
         "id":30,
         "dateField":"2093-01-24T07:06:53Z",
         "doubleField":992.49123409219999,
         "booleanField":true,
         "stringField":"Schowalter Branch",
         "optionalStringField":"15"
      },
      {  
         "intField":282,
         "id":38,
         "dateField":"2092-03-01T03:59:20Z",
         "doubleField":194.4565969041,
         "booleanField":true,
         "stringField":"Ignacio Springs",
         "optionalStringField":"20"
      },
      {  
         "booleanField":true,
         "id":32,
         "stringField":"Braun Rapid",
         "doubleField":445.48755242620001,
         "dateField":"2078-05-13T15:50:20Z",
         "intField":583
      }
   ],
   "nextPageCursor":"W3sia2V5IjoiZGF0ZUZpZWxkIiwidmFsdWUiOjMzODQ2Nzc4NjgsImRpcmVjdGlvbiI6ImRlc2NlbmRpbmcifSx7ImtleSI6ImlkIiwidmFsdWUiOjQ2LCJkaXJlY3Rpb24iOiJhc2NlbmRpbmcifV0="
}

Then use the nextPageCursor in your next request:

curl "http://localhost:8080/modelsByDate?limit=5&cursor=W3sia2V5IjoiZGF0ZUZpZWxkIiwidmFsdWUiOjMzODQ2Nzc4NjgsImRpcmVjdGlvbiI6ImRlc2NlbmRpbmcifSx7ImtleSI6ImlkIiwidmFsdWUiOjQ2LCJkaXJlY3Rpb24iOiJhc2NlbmRpbmcifV0="

{  
   "remaining":40,
   "data":[  
      {  
         "booleanField":false,
         "id":46,
         "stringField":"Aditya Crossroad",
         "doubleField":226.63376066519999,
         "dateField":"2077-04-03T12:17:48Z",
         "intField":149
      },
      {  
         "booleanField":true,
         "id":18,
         "stringField":"Emmitt Ridges",
         "doubleField":90.362315319999993,
         "dateField":"2074-09-14T07:46:27Z",
         "intField":990
      },
      {  
         "booleanField":true,
         "id":27,
         "stringField":"Evelyn Rest",
         "doubleField":371.72649320490001,
         "dateField":"2072-11-21T19:26:05Z",
         "intField":77
      },
      {  
         "intField":351,
         "id":45,
         "dateField":"2071-04-18T00:59:09Z",
         "doubleField":45.889304030200002,
         "booleanField":true,
         "stringField":"Fisher Trail",
         "optionalStringField":"24"
      },
      {  
         "intField":476,
         "id":25,
         "dateField":"2070-04-10T15:16:10Z",
         "doubleField":810.14490844919999,
         "booleanField":false,
         "stringField":"Paucek Plains",
         "optionalStringField":"12"
      }
   ],
   "nextPageCursor":"W3sia2V5IjoiZGF0ZUZpZWxkIiwidmFsdWUiOjMwOTM3NTk5MzcsImRpcmVjdGlvbiI6ImRlc2NlbmRpbmcifSx7ImtleSI6ImlkIiwidmFsdWUiOjYsImRpcmVjdGlvbiI6ImFzY2VuZGluZyJ9XQ=="
}

When there are no more results, a cursor will not be returned.

Compound Sorts

Sorting on multiple properties works as well.

NOTE:

In order to break ties, the last sort must be on a unique property, otherwise a sort on a default unique property (Fluent id) will be applied.

router.get("modelsByBooleanAndString") { request -> Future<CursorPage<KitchenSink>> in
    return try KitchenSink.paginate(database: Database,
                     sorts: .descending(\.booleanField), .ascending(\.stringField))
}

Dynamic Sorting

You can allow the client to dynamically dictate how the results are sorted via query parameters.

⚠️ WARNING:

Because the dynamic sorting API has no way to resolve KeyPaths from string based parameters, it uses runtime reflection to build the cursor. You may not want to use this API in production until Swift ABI is stable.

Setup a dynamically sortable request handler like so:

router.get("dynamicModels") { request -> Future<CursorPage<KitchenSink>> in
    return try KitchenSink.paginate(dynamicdatabase: Database)
}

Then in your request, each sorts and orders via the sort[] and order[] parameters respectively (order matters): curl "http://localhost:8080/dynamicModels?limit=5&sort[]=booleanField&order[]=descending&sort[]=stringField&order[]=ascending"

TODO

• Optional support
• Compound sorts
• Dynamic sorting
• Allow for additional filters on queries
• Aggregate support (might be some use cases here)
• Nil sort order preference
• Allow for customization of CursorPage’s JSON structure
• Integrate CircleCI
• Explore database specific optimized implementations (benchmark first to see if needed)

Contributing

We would love you to contribute to CursorPagination, check the CONTRIBUTING file for more info.

License

CursorPagination is available under the MIT license. See the LICENSE file for more info.