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keyset.ex
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keyset.ex
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defmodule Ash.Page.Keyset do
@moduledoc """
A page of results from `keyset` based pagination.
The results are generated with a `keyset` metadata,
which can be used to fetch the next/previous pages.
"""
defstruct [:results, :count, :before, :after, :limit, :rerun, :more?]
@type t :: %__MODULE__{}
def new(results, count, sort, original_query, more?, opts) do
%__MODULE__{
results: data_with_keyset(results, sort),
count: count,
before: opts[:page][:before],
after: opts[:page][:after],
limit: opts[:page][:limit],
more?: more?,
rerun: {original_query, opts}
}
end
def data_with_keyset(results, sort) do
fields_in_keyset =
sort
|> Keyword.keys()
|> Enum.sort()
Enum.map(results, fn result ->
Map.update!(
result,
:__metadata__,
&Map.put(&1, :keyset, keyset(result, fields_in_keyset))
)
end)
end
def filter(values, sort, after_or_before) when after_or_before in [:after, :before] do
sort_fields =
sort
|> Keyword.keys()
|> Enum.sort()
with {:ok, decoded} <- decode_values(values),
{:ok, zipped} <- zip_fields(sort_fields, decoded) do
field_values =
Enum.map(sort, fn {field, direction} ->
{field, direction, Keyword.get(zipped, field)}
end)
{:ok, filters(field_values, after_or_before)}
end
end
defp decode_values(values) do
{:ok,
values
|> URI.decode_www_form()
|> Base.decode64!()
|> non_executable_binary_to_term([:safe])}
rescue
e ->
{:error, e}
end
defp filters(keyset, after_or_before) do
[or: do_filters(keyset, after_or_before)]
end
defp do_filters([], _), do: []
defp do_filters([{field, direction, value} | rest], after_or_before) do
operator = operator(after_or_before, direction)
# keyset pagination is done like so
# (x > a) OR
# (x = a AND y > b) OR
# (x = a AND y = b AND z > c) OR
[[{field, [{operator, value}]}]] ++
Enum.map(do_filters(rest, after_or_before), fn nested ->
[[{field, [eq: value]}]] ++ nested
end)
end
defp operator(:after, :asc), do: :gt
defp operator(:after, :asc_nils_first), do: :gt
defp operator(:after, :asc_nils_last), do: :gt
defp operator(:after, :desc), do: :lt
defp operator(:after, :desc_nulls_first), do: :lt
defp operator(:after, :desc_nulls_last), do: :lt
defp operator(:before, :asc), do: :lt
defp operator(:before, :asc_nils_first), do: :lt
defp operator(:before, :asc_nils_last), do: :lt
defp operator(:before, :desc), do: :gt
defp operator(:before, :desc_nulls_first), do: :gt
defp operator(:before, :desc_nulls_last), do: :gt
defp zip_fields(pkey, values, acc \\ [])
defp zip_fields([], [], acc), do: {:ok, Enum.reverse(acc)}
defp zip_fields([pkey | rest_pkey], [value | rest_values], acc) do
zip_fields(rest_pkey, rest_values, [{pkey, value} | acc])
end
defp zip_fields(_, _, _), do: {:error, "Invalid keyset"}
defp keyset(record, fields) do
record
|> field_values(fields)
|> :erlang.term_to_binary()
|> Base.encode64()
|> URI.encode_www_form()
end
defp field_values(record, fields) do
Enum.map(fields, &Map.get(record, &1))
end
@doc """
A restricted version of `:erlang.binary_to_term/2` that forbids
*executable* terms, such as anonymous functions.
The `opts` are given to the underlying `:erlang.binary_to_term/2`
call, with an empty list as a default.
By default this function does not restrict atoms, as an atom
interned in one node may not yet have been interned on another
(except for releases, which preload all code).
If you want to avoid atoms from being created, then you can pass
`[:safe]` as options, as that will also enable the safety mechanisms
from `:erlang.binary_to_term/2` itself.
Ripped from https://github.com/elixir-plug/plug_crypto/blob/v1.2.0/lib/plug/crypto.ex
"""
defdelegate non_executable_binary_to_term(binary, opts), to: Ash.Helpers
end