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ash/documentation/topics/advanced/pagination.livemd
Riccardo Binetti 421905c163
docs: add pagination guide in advanced topics (#1113)
2024-05-29 07:35:34 -04:00

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<!-- livebook:{"persist_outputs":true} -->
# Pagination
```elixir
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](https://hexdocs.pm/ash/dsl-ash-resource.html#actions-read-pagination).
> ### 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.
<!-- livebook:{"force_markdown":true} -->
```elixir
Logger.configure(level: :debug)
```
### Define some resources for our purpose
```elixir
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
```
<!-- livebook:{"output":true} -->
```
{: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
```elixir
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)
```
<!-- livebook:{"output":true} -->
```
[
#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.
```elixir
page = Domain.list_posts!(page: [limit: 2])
```
<!-- livebook:{"output":true} -->
```
%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
```elixir
page.results
```
<!-- livebook:{"output":true} -->
```
[
#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
```elixir
page.more?
```
<!-- livebook:{"output":true} -->
```
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
```elixir
next_offset = page.offset + page.limit
second_page = Domain.list_posts!(page: [limit: 2, offset: next_offset])
```
<!-- livebook:{"output":true} -->
```
%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.
```elixir
last_page = Ash.page!(second_page, :next)
```
<!-- livebook:{"output":true} -->
```
%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:
```elixir
last_page.more?
```
<!-- livebook:{"output":true} -->
```
false
```
### Keyset pagination
When using keyset pagination, a `%Ash.Page.Keyset{}` struct is returned from read actions.
```elixir
page = Domain.list_posts_with_keyset!(page: [limit: 2])
```
<!-- livebook:{"output":true} -->
```
%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
```elixir
page.results
```
<!-- livebook:{"output":true} -->
```
[
#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`.
```elixir
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])
```
<!-- livebook:{"output":true} -->
```
%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
```elixir
last_page = Ash.page!(second_page, :next)
last_page.more?
```
<!-- livebook:{"output":true} -->
```
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.
```elixir
%Ash.Page.Offset{results: [_, last]} = Domain.list_posts!(page: [limit: 2])
Domain.list_posts!(page: [limit: 2, after: last.__metadata__.keyset])
```
<!-- livebook:{"output":true} -->
```
%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.
```elixir
page = Domain.list_posts!(page: [limit: 2, count: true])
page.count
```
<!-- livebook:{"output":true} -->
```
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.
```elixir
paginated_comments =
Comment
|> Ash.Query.page(limit: 2)
first_post =
Domain.list_posts!(load: [comments: paginated_comments])
|> List.first()
first_post.comments
```
<!-- livebook:{"output":true} -->
```
%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<resource: Comment, sort: [created_at: :asc], page: [limit: 2]>,
[authorize?: true, actor: nil, tracer: []]},
more?: true
}
```
You can use all the methods describe above to navigate relationship pages and retrieve their count
```elixir
second = Ash.page!(first_post.comments, :next)
```
<!-- livebook:{"output":true} -->
```
%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
}
```
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