Pagination

Mix.install([{:ash, "~> 3.0"}], consolidate_protocols: false)
Logger.configure(level: :warning)

Pagination in Ash

Ash has built-in support for two kinds of pagination: offset and keyset. You can perform pagination by passing the :page option to read actions, or using Ash.Query.page/2 on the query. The page options vary depending on which kind of pagination you want to perform.

Pagination support is configured on a per-action basis. A single action can support both kinds of pagination if desired, but typically you would use one or the other. Read actions generated with defaults [:read] support both offset and keyset pagination, for other read actions you have to configure the pagination section.

> ### Check the updated query return type! > > Pagination will modify the return type of calling the query action. > > Without pagination, Ash will return a list of records. > > But with pagination, Ash will return an Ash.Page.Offset struct (for offset pagination) or Ash.Page.Keyset struct (for keyset pagination). Both structs contain the list of records in the results key of the struct.

Offset Pagination

Offset pagination is done via providing a limit and an offset when making queries.

• The limit determines how many records should be returned in the query.
• The offset describes how many records from the beginning should be skipped.

Pros of offset pagination

• Simple to think about
• Possible to skip to a page by number. E.g the 5th page of 10 records is offset: 40
• Easy to reason about what page you are currently on (if the total number of records is requested)
• Can go to the last page (though data may have changed between calculating the last page details, and requesting it)

Cons of offset pagination

• Does not perform well on large datasets (if you have to ask if your dataset is “large”, it probably isn’t)
• When moving between pages, if data was created or deleted, individual records may be missing or appear on multiple pages

Keyset Pagination

Keyset pagination is done via providing an after or before option, as well as a limit.

• The limit determines how many records should be returned in the query.
• The after or before value should be a keyset value that has been returned from a previous request. Keyset values are returned whenever there is any read action on a resource that supports keyset pagination, and they are stored in the __metadata__ key of each record.

> ### Keysets are directly tied to the sorting applied to the query > > You can’t change the sort applied to a request being paginated, and use the same keyset. If you want to change the sort, but keep the record who’s keyset you are using in the before or after option, you must first request the individual record, with the new sort applied. Then, you can use the new keyset.

Pros of keyset pagination

• Performs very well on large datasets (assuming indices exist on the columns being sorted on)
• Behaves well as data changes. The record specified will always be the first or last item in the page

Cons of keyset paginations

• A bit more complex to use
• Can’t go to a specific page number

Counting records

When calling an action that uses pagination, the full count of records can be requested by adding the option count: true to the page options. Note that this will perform a second query to fetch the count, which can be expensive on large data sets.

Relationship pagination

In addition to paginating root data, Ash is also capable of paginating relationships when you load them. To do this, pass a custom query in the load and call Ash.Query.page/2 on it.

This can be leveraged by extensions to provide arbitrarily nested pagination, or it can be used directly in code to split data processing when dealing with relationship with a high cardinality.

Pagination example

Modify the setup block and configure the log level to :debug to see logs from the ETS data layer.

Logger.configure(level: :debug)

Define some resources for our purpose

defmodule Post do
  use Ash.Resource,
    domain: Domain,
    data_layer: Ash.DataLayer.Ets

  attributes do
    uuid_primary_key(:id)
    attribute(:title, :string, allow_nil?: false)
    attribute(:text, :string, allow_nil?: false)
  end

  actions do
    defaults(create: [:title, :text])

    read :read do
      primary?(true)
      prepare(build(sort: :title))

      pagination do
        required?(false)
        offset?(true)
        keyset?(true)
        countable(true)
      end
    end

    read :keyset do
      prepare(build(sort: :title))
      pagination(keyset?: true)
    end

    update :add_comment do
      require_atomic?(false)
      argument(:comment, :string, allow_nil?: false)
      change(manage_relationship(:comment, :comments, value_is_key: :text, type: :create))
    end
  end

  relationships do
    has_many(:comments, Comment, sort: [:created_at])
  end
end

defmodule Comment do
  use Ash.Resource,
    domain: Domain,
    data_layer: Ash.DataLayer.Ets

  attributes do
    uuid_primary_key(:id)
    attribute(:text, :string, allow_nil?: false)
    create_timestamp(:created_at)
  end

  actions do
    defaults([:read, create: [:text, :post_id], update: [:text, :post_id]])
  end

  relationships do
    belongs_to(:post, Post, sort: [:created_at])
  end
end

defmodule Domain do
  use Ash.Domain,
    validate_config_inclusion?: false

  resources do
    resource Post do
      define(:list_posts, action: :read)
      define(:list_posts_with_keyset, action: :keyset)
      define(:create_post, action: :create, args: [:title, :text])
      define(:add_comment_to_post, action: :add_comment, args: [:comment])
    end

    resource(Comment)
  end
end

{:module, Domain, <<70, 79, 82, 49, 0, 2, 31, ...>>,
 [
   Ash.Domain.Dsl.Resources.Resource,
   Ash.Domain.Dsl.Resources.Options,
   Ash.Domain.Dsl,
   %{opts: [], entities: [...]},
   Ash.Domain.Dsl,
   Ash.Domain.Dsl.Resources.Options,
   ...
 ]}

Create 5 posts with 5 comments each

for post_idx <- 1..5 do
  post = Domain.create_post!("post #{post_idx}", "text #{post_idx}")

  for comment_idx <- 1..5 do
    Domain.add_comment_to_post!(post, "comment #{comment_idx}")
  end
end

Domain.list_posts!(load: :comments)

[
  #Post<
    comments: [
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "6cdea87b-cb69-4dc5-9ff3-54fb46bd70b0",
        text: "comment 1",
        created_at: ~U[2024-05-28 21:32:59.013913Z],
        post_id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "c653e92c-fe2f-4011-84c8-ace28ebbb207",
        text: "comment 2",
        created_at: ~U[2024-05-28 21:32:59.021204Z],
        post_id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "aa207735-0a02-4b51-b5f6-69564a2a6365",
        text: "comment 3",
        created_at: ~U[2024-05-28 21:32:59.022890Z],
        post_id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "09f9cdfe-5a88-4f6a-a8d9-2f8aa312efb8",
        text: "comment 4",
        created_at: ~U[2024-05-28 21:32:59.024526Z],
        post_id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "9b92edf4-e79e-4870-9dd0-9130863a9715",
        text: "comment 5",
        created_at: ~U[2024-05-28 21:32:59.026132Z],
        post_id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
        aggregates: %{},
        calculations: %{},
        ...
      >
    ],
    __meta__: #Ecto.Schema.Metadata<:loaded>,
    id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
    title: "post 1",
    text: "text 1",
    aggregates: %{},
    calculations: %{},
    ...
  >,
  #Post<
    comments: [
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "9a87a3a0-6930-4920-9345-8227b861c2ed",
        text: "comment 1",
        created_at: ~U[2024-05-28 21:32:59.028515Z],
        post_id: "78cd10f0-a509-4602-861f-24652c68d54b",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "a5107151-5519-4925-ab73-aef75274cd4a",
        text: "comment 2",
        created_at: ~U[2024-05-28 21:32:59.030176Z],
        post_id: "78cd10f0-a509-4602-861f-24652c68d54b",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "0d7e9835-25a0-4df9-bb41-06aa964dc677",
        text: "comment 3",
        created_at: ~U[2024-05-28 21:32:59.031780Z],
        post_id: "78cd10f0-a509-4602-861f-24652c68d54b",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "7c6663a8-6a36-4c9a-a947-a70436add8be",
        text: "comment 4",
        created_at: ~U[2024-05-28 21:32:59.033389Z],
        post_id: "78cd10f0-a509-4602-861f-24652c68d54b",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "4a54ee7f-18fe-401b-9a86-7c768bc52a1d",
        text: "comment 5",
        created_at: ~U[2024-05-28 21:32:59.034976Z],
        post_id: "78cd10f0-a509-4602-861f-24652c68d54b",
        aggregates: %{},
        calculations: %{},
        ...
      >
    ],
    __meta__: #Ecto.Schema.Metadata<:loaded>,
    id: "78cd10f0-a509-4602-861f-24652c68d54b",
    title: "post 2",
    text: "text 2",
    aggregates: %{},
    calculations: %{},
    ...
  >,
  #Post<
    comments: [
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "9d01f179-4220-4796-bb7d-63527385e36b",
        text: "comment 1",
        created_at: ~U[2024-05-28 21:32:59.037470Z],
        post_id: "ab8e9909-2a6c-42d7-bae9-09fad4356ea4",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "49b7a671-bc6f-4772-b8f8-73b2a4c75b34",
        text: "comment 2",
        created_at: ~U[2024-05-28 21:32:59.039117Z],
        post_id: "ab8e9909-2a6c-42d7-bae9-09fad4356ea4",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "7d2ee81c-696f-4190-8d1a-45702bfaaef2",
        text: "comment 3",
        created_at: ~U[2024-05-28 21:32:59.040795Z],
        post_id: "ab8e9909-2a6c-42d7-bae9-09fad4356ea4",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "98d80b57-b911-44f5-9a63-5db90c1a0d57",
        text: "comment 4",
        created_at: ~U[2024-05-28 21:32:59.042457Z],
        post_id: "ab8e9909-2a6c-42d7-bae9-09fad4356ea4",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "a0f08863-ec7f-4eba-b9f5-f9d7764dc934",
        text: "comment 5",
        created_at: ~U[2024-05-28 21:32:59.044061Z],
        post_id: "ab8e9909-2a6c-42d7-bae9-09fad4356ea4",
        aggregates: %{},
        calculations: %{},
        ...
      >
    ],
    __meta__: #Ecto.Schema.Metadata<:loaded>,
    id: "ab8e9909-2a6c-42d7-bae9-09fad4356ea4",
    title: "post 3",
    text: "text 3",
    aggregates: %{},
    calculations: %{},
    ...
  >,
  #Post<
    comments: [
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "2a57aa5f-0431-4d7b-a054-3bf0fc6cb2e8",
        text: "comment 1",
        created_at: ~U[2024-05-28 21:32:59.046395Z],
        post_id: "91d639c2-4a2c-4931-b446-543e118644f1",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "1604094f-864e-4df3-9365-a16a77ace0ba",
        text: "comment 2",
        created_at: ~U[2024-05-28 21:32:59.048111Z],
        post_id: "91d639c2-4a2c-4931-b446-543e118644f1",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "6153ecb4-4668-4afb-94c8-b1e57ed1a187",
        text: "comment 3",
        created_at: ~U[2024-05-28 21:32:59.049749Z],
        post_id: "91d639c2-4a2c-4931-b446-543e118644f1",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "0844db43-39f7-41c3-aa74-41238b0882c9",
        text: "comment 4",
        created_at: ~U[2024-05-28 21:32:59.051385Z],
        post_id: "91d639c2-4a2c-4931-b446-543e118644f1",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "b22db803-cad0-4d90-ada1-944f0abdd304",
        text: "comment 5",
        created_at: ~U[2024-05-28 21:32:59.053563Z],
        post_id: "91d639c2-4a2c-4931-b446-543e118644f1",
        aggregates: %{},
        calculations: %{},
        ...
      >
    ],
    __meta__: #Ecto.Schema.Metadata<:loaded>,
    id: "91d639c2-4a2c-4931-b446-543e118644f1",
    title: "post 4",
    text: "text 4",
    aggregates: %{},
    calculations: %{},
    ...
  >,
  #Post<
    comments: [
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "7b5fc51b-8e68-441e-bcd0-e52a0158e779",
        text: "comment 1",
        created_at: ~U[2024-05-28 21:32:59.056055Z],
        post_id: "b0b20225-17f0-4bd1-8bd1-681e63ee26a8",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "e3f01413-c79c-44ef-abd9-6cb27a3b31fc",
        text: "comment 2",
        created_at: ~U[2024-05-28 21:32:59.057708Z],
        post_id: "b0b20225-17f0-4bd1-8bd1-681e63ee26a8",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "a461c559-5036-4113-93be-3f531af4d2f3",
        text: "comment 3",
        created_at: ~U[2024-05-28 21:32:59.059418Z],
        post_id: "b0b20225-17f0-4bd1-8bd1-681e63ee26a8",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "a704a781-3ff2-479c-b428-d8a414223f00",
        text: "comment 4",
        created_at: ~U[2024-05-28 21:32:59.061034Z],
        post_id: "b0b20225-17f0-4bd1-8bd1-681e63ee26a8",
        aggregates: %{},
        calculations: %{},
        ...
      >,
      #Comment<
        post: #Ash.NotLoaded<:relationship, field: :post>,
        __meta__: #Ecto.Schema.Metadata<:loaded>,
        id: "2d9e9279-ef21-4dd4-bdc6-adc3597fefb2",
        text: "comment 5",
        created_at: ~U[2024-05-28 21:32:59.062631Z],
        post_id: "b0b20225-17f0-4bd1-8bd1-681e63ee26a8",
        aggregates: %{},
        calculations: %{},
        ...
      >
    ],
    __meta__: #Ecto.Schema.Metadata<:loaded>,
    id: "b0b20225-17f0-4bd1-8bd1-681e63ee26a8",
    title: "post 5",
    text: "text 5",
    aggregates: %{},
    calculations: %{},
    ...
  >
]

Offset pagination

When using offset pagination, a %Ash.Page.Offset{} struct is returned from read actions.

page = Domain.list_posts!(page: [limit: 2])

%Ash.Page.Offset{
  results: [
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
      title: "post 1",
      text: "text 1",
      aggregates: %{},
      calculations: %{},
      ...
    >,
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "78cd10f0-a509-4602-861f-24652c68d54b",
      title: "post 2",
      text: "text 2",
      aggregates: %{},
      calculations: %{},
      ...
    >
  ],
  limit: 2,
  offset: 0,
  count: nil,
  rerun: {#Ash.Query<
     resource: Post,
     sort: [title: :asc],
     select: [:id, :title, :text],
     page: [limit: 2]
   >, [authorize?: true, reuse_values?: false, return_query?: false]},
  more?: true
}

You can find the results in the results field of the page

page.results

[
  #Post<
    comments: #Ash.NotLoaded<:relationship, field: :comments>,
    __meta__: #Ecto.Schema.Metadata<:loaded>,
    id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
    title: "post 1",
    text: "text 1",
    aggregates: %{},
    calculations: %{},
    ...
  >,
  #Post<
    comments: #Ash.NotLoaded<:relationship, field: :comments>,
    __meta__: #Ecto.Schema.Metadata<:loaded>,
    id: "78cd10f0-a509-4602-861f-24652c68d54b",
    title: "post 2",
    text: "text 2",
    aggregates: %{},
    calculations: %{},
    ...
  >
]

The more? field contains a boolean indicating if there are more pages available

page.more?

true

Retrieving the next page

You can calculate the next offset with the information available in the page and pass it in the page options to retrieve the following page

next_offset = page.offset + page.limit
second_page = Domain.list_posts!(page: [limit: 2, offset: next_offset])

%Ash.Page.Offset{
  results: [
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "ab8e9909-2a6c-42d7-bae9-09fad4356ea4",
      title: "post 3",
      text: "text 3",
      aggregates: %{},
      calculations: %{},
      ...
    >,
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "91d639c2-4a2c-4931-b446-543e118644f1",
      title: "post 4",
      text: "text 4",
      aggregates: %{},
      calculations: %{},
      ...
    >
  ],
  limit: 2,
  offset: 2,
  count: nil,
  rerun: {#Ash.Query<
     resource: Post,
     sort: [title: :asc],
     select: [:id, :title, :text],
     page: [limit: 2, offset: 2]
   >, [authorize?: true, reuse_values?: false, return_query?: false]},
  more?: true
}

If you have the current page in memory, you can also use Ash.page!/2 to navigate between pages.

last_page = Ash.page!(second_page, :next)

%Ash.Page.Offset{
  results: [
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "b0b20225-17f0-4bd1-8bd1-681e63ee26a8",
      title: "post 5",
      text: "text 5",
      aggregates: %{},
      calculations: %{},
      ...
    >
  ],
  limit: 2,
  offset: 4,
  count: nil,
  rerun: {#Ash.Query<
     resource: Post,
     sort: [title: :asc],
     select: [:title, :id, :text],
     page: [offset: 4, limit: 2]
   >, [authorize?: true, reuse_values?: false, return_query?: false]},
  more?: false
}

And since we had 5 posts, this should be the last page:

last_page.more?

false

Keyset pagination

When using keyset pagination, a %Ash.Page.Keyset{} struct is returned from read actions.

page = Domain.list_posts_with_keyset!(page: [limit: 2])

%Ash.Page.Keyset{
  results: [
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
      title: "post 1",
      text: "text 1",
      aggregates: %{},
      calculations: %{},
      ...
    >,
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "78cd10f0-a509-4602-861f-24652c68d54b",
      title: "post 2",
      text: "text 2",
      aggregates: %{},
      calculations: %{},
      ...
    >
  ],
  count: nil,
  before: nil,
  after: nil,
  limit: 2,
  rerun: {#Ash.Query<
     resource: Post,
     sort: [title: :asc],
     select: [:id, :title, :text],
     page: [limit: 2]
   >, [authorize?: true, reuse_values?: false, return_query?: false]},
  more?: true
}

results and more? work in the same way as offset pagination

page.results

[
  #Post<
    comments: #Ash.NotLoaded<:relationship, field: :comments>,
    __meta__: #Ecto.Schema.Metadata<:loaded>,
    id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
    title: "post 1",
    text: "text 1",
    aggregates: %{},
    calculations: %{},
    ...
  >,
  #Post<
    comments: #Ash.NotLoaded<:relationship, field: :comments>,
    __meta__: #Ecto.Schema.Metadata<:loaded>,
    id: "78cd10f0-a509-4602-861f-24652c68d54b",
    title: "post 2",
    text: "text 2",
    aggregates: %{},
    calculations: %{},
    ...
  >
]

Retrieving the next page

To retrieve the next page, you have to pass the keyset of the last record in the current page. The keyset is stored in record.__metadata__.keyset.

last_keyset =
  page.results
  |> List.last()
  |> Map.get(:__metadata__)
  |> Map.get(:keyset)

second_page = Domain.list_posts_with_keyset!(page: [limit: 2, after: last_keyset])

%Ash.Page.Keyset{
  results: [
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "ab8e9909-2a6c-42d7-bae9-09fad4356ea4",
      title: "post 3",
      text: "text 3",
      aggregates: %{},
      calculations: %{},
      ...
    >,
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "91d639c2-4a2c-4931-b446-543e118644f1",
      title: "post 4",
      text: "text 4",
      aggregates: %{},
      calculations: %{},
      ...
    >
  ],
  count: nil,
  before: nil,
  after: "g2wAAAACbQAAAAZwb3N0IDJtAAAAJDc4Y2QxMGYwLWE1MDktNDYwMi04NjFmLTI0NjUyYzY4ZDU0Ymo=",
  limit: 2,
  rerun: {#Ash.Query<
     resource: Post,
     sort: [title: :asc],
     select: [:id, :title, :text],
     page: [
       limit: 2,
       after: "g2wAAAACbQAAAAZwb3N0IDJtAAAAJDc4Y2QxMGYwLWE1MDktNDYwMi04NjFmLTI0NjUyYzY4ZDU0Ymo="
     ]
   >, [authorize?: true, reuse_values?: false, return_query?: false]},
  more?: true
}

Ash.page!/2 works with keyset pagination too

last_page = Ash.page!(second_page, :next)

last_page.more?

false

Actions supporting both offset and keyset pagination

If an action supports both offset and keyset pagination (e.g. default read actions), offset pagination is used by default when page options only contain limit. However, the records will have the keyset in the metadata, so keyset pagination can be performed on next pages.

%Ash.Page.Offset{results: [_, last]} = Domain.list_posts!(page: [limit: 2])

Domain.list_posts!(page: [limit: 2, after: last.__metadata__.keyset])

%Ash.Page.Keyset{
  results: [
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "ab8e9909-2a6c-42d7-bae9-09fad4356ea4",
      title: "post 3",
      text: "text 3",
      aggregates: %{},
      calculations: %{},
      ...
    >,
    #Post<
      comments: #Ash.NotLoaded<:relationship, field: :comments>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "91d639c2-4a2c-4931-b446-543e118644f1",
      title: "post 4",
      text: "text 4",
      aggregates: %{},
      calculations: %{},
      ...
    >
  ],
  count: nil,
  before: nil,
  after: "g2wAAAACbQAAAAZwb3N0IDJtAAAAJDc4Y2QxMGYwLWE1MDktNDYwMi04NjFmLTI0NjUyYzY4ZDU0Ymo=",
  limit: 2,
  rerun: {#Ash.Query<
     resource: Post,
     sort: [title: :asc],
     select: [:id, :title, :text],
     page: [
       limit: 2,
       after: "g2wAAAACbQAAAAZwb3N0IDJtAAAAJDc4Y2QxMGYwLWE1MDktNDYwMi04NjFmLTI0NjUyYzY4ZDU0Ymo="
     ]
   >, [authorize?: true, reuse_values?: false, return_query?: false]},
  more?: true
}

Retrieving count

Both %Ash.Page.Offset{} and %Ash.Page.Keyset{} have a count field that contains the total count of the items that are being paginated when count: true is passed in the page options.

page = Domain.list_posts!(page: [limit: 2, count: true])

page.count

5

Relationship pagination

To paginate a relationship, pass a query customized with the page options to the load statement. This works both on paginated and unpaginated root data, and relationships can load arbitrarily nested paginated relationships.

paginated_comments =
  Comment
  |> Ash.Query.page(limit: 2)

first_post =
  Domain.list_posts!(load: [comments: paginated_comments])
  |> List.first()

first_post.comments

%Ash.Page.Offset{
  results: [
    #Comment<
      post: #Ash.NotLoaded<:relationship, field: :post>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "6cdea87b-cb69-4dc5-9ff3-54fb46bd70b0",
      text: "comment 1",
      created_at: ~U[2024-05-28 21:32:59.013913Z],
      post_id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
      aggregates: %{},
      calculations: %{},
      ...
    >,
    #Comment<
      post: #Ash.NotLoaded<:relationship, field: :post>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "c653e92c-fe2f-4011-84c8-ace28ebbb207",
      text: "comment 2",
      created_at: ~U[2024-05-28 21:32:59.021204Z],
      post_id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
      aggregates: %{},
      calculations: %{},
      ...
    >
  ],
  limit: 2,
  offset: 0,
  count: nil,
  rerun: {#Ash.Query,
   [authorize?: true, actor: nil, tracer: []]},
  more?: true
}

You can use all the methods describe above to navigate relationship pages and retrieve their count

second = Ash.page!(first_post.comments, :next)

%Ash.Page.Offset{
  results: [
    #Comment<
      post: #Ash.NotLoaded<:relationship, field: :post>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "aa207735-0a02-4b51-b5f6-69564a2a6365",
      text: "comment 3",
      created_at: ~U[2024-05-28 21:32:59.022890Z],
      post_id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
      aggregates: %{},
      calculations: %{},
      ...
    >,
    #Comment<
      post: #Ash.NotLoaded<:relationship, field: :post>,
      __meta__: #Ecto.Schema.Metadata<:loaded>,
      id: "09f9cdfe-5a88-4f6a-a8d9-2f8aa312efb8",
      text: "comment 4",
      created_at: ~U[2024-05-28 21:32:59.024526Z],
      post_id: "6eb22ea7-184c-4cae-9054-0d1a0474db61",
      aggregates: %{},
      calculations: %{},
      ...
    >
  ],
  limit: 2,
  offset: 2,
  count: nil,
  rerun: {#Ash.Query<
     resource: Comment,
     sort: [created_at: :asc],
     select: [:id, :text, :created_at, :post_id],
     page: [offset: 2, limit: 2]
   >, [reuse_values?: false, return_query?: false, authorize?: true, actor: nil, tracer: []]},
  more?: true
}