Merge pull request #36 from profiq/feature/page-size-and-offset

Add support for proper offsets and custom page sizes

Author: dhrdlicka

config/config.exs

@@ -59,10 +59,7 @@ config :logger, :console,
 config :phoenix, :json_library, Jason
 
 # Configure Flop
-config :flop,
-  repo: SWAPI.Repo,
-  pagination_types: [:page],
-  default_limit: 10
+config :flop, repo: SWAPI.Repo
 
 # Import environment specific config. This must remain at the bottom
 # of this file so it overrides the configuration defined above.

lib/swapi/films.ex

@@ -7,7 +7,7 @@ defmodule SWAPI.Films do
   alias SWAPI.Schemas.Film
 
   import Ecto.Query, warn: false
-  import SWAPI.Util
+  import SWAPI.Pagination
 
   def preload_all(film) do
     Repo.preload(film, [:species, :starships, :vehicles, :characters, :planets])

lib/swapi/pagination.ex

@@ -0,0 +1,79 @@
+defmodule SWAPI.Pagination do
+  @moduledoc """
+  Utility functions
+  """
+
+  @type pagination_method :: :page | :offset
+  @type page_info() :: %{
+          count: non_neg_integer,
+          next: {pagination_method, non_neg_integer} | nil,
+          previous: {pagination_method, non_neg_integer} | nil
+        }
+
+  @default_page_size 10
+
+  @doc """
+  Queries the given Ecto queryable with pagination.
+  """
+  @spec paginate(Ecto.Queryable.t(), map()) :: {:ok, {list, page_info}} | {:error, atom}
+  def paginate(query, params) do
+    with {:ok, params} <- check_pagination_methods(params) do
+      do_paginate(query, params)
+    end
+  end
+
+  defp check_pagination_methods(params) do
+    {methods, _} = Map.split(params, ~w(page offset))
+
+    if Enum.count(methods) <= 1 do
+      {:ok, params}
+    else
+      {:error, :bad_request}
+    end
+  end
+
+  defp do_paginate(query, %{"page" => page} = params) when is_binary(page) do
+    with {:ok, page} <- parse_integer(page),
+         {:ok, page_size} <- parse_integer(params["limit"], @default_page_size),
+         {list, meta} <- Flop.validate_and_run!(query, %Flop{page: page, page_size: page_size}) do
+      {:ok,
+       {list,
+        %{
+          count: meta.total_count,
+          next: if(meta.next_page, do: {:page, meta.next_page}),
+          previous: if(meta.previous_page, do: {:page, meta.previous_page})
+        }}}
+    end
+  end
+
+  defp do_paginate(query, %{"offset" => offset} = params) when is_binary(offset) do
+    with {:ok, offset} <- parse_integer(offset),
+         {:ok, limit} <- parse_integer(params["limit"], @default_page_size),
+         {list, meta} <- Flop.validate_and_run!(query, %Flop{offset: offset, limit: limit}) do
+      {:ok,
+       {list,
+        %{
+          count: meta.total_count,
+          next: if(meta.next_offset, do: {:offset, meta.next_offset}),
+          previous: if(meta.previous_offset, do: {:offset, meta.previous_offset})
+        }}}
+    end
+  end
+
+  defp do_paginate(query, _), do: do_paginate(query, %{"page" => "1"})
+
+  defp parse_integer(value) do
+    case Integer.parse(value) do
+      :error -> {:error, :bad_request}
+      {value, _} -> {:ok, value}
+    end
+  end
+
+  defp parse_integer(value, default_value) do
+    if value do
+      parse_integer(value)
+    else
+      {:ok, default_value}
+    end
+  end
+end

lib/swapi/people.ex

@@ -7,7 +7,7 @@ defmodule SWAPI.People do
   alias SWAPI.Schemas.Person
 
   import Ecto.Query, warn: false
-  import SWAPI.Util
+  import SWAPI.Pagination
 
   def preload_all(person) do
     Repo.preload(person, [:homeworld, :films, :species, :starships, :vehicles])

lib/swapi/planets.ex

@@ -7,7 +7,7 @@ defmodule SWAPI.Planets do
   alias SWAPI.Schemas.Planet
 
   import Ecto.Query, warn: false
-  import SWAPI.Util
+  import SWAPI.Pagination
 
   def preload_all(planet) do
     Repo.preload(planet, [:residents, :films])

lib/swapi/species.ex

@@ -7,7 +7,7 @@ defmodule SWAPI.Species do
   alias SWAPI.Schemas.Species
 
   import Ecto.Query, warn: false
-  import SWAPI.Util
+  import SWAPI.Pagination
 
   def preload_all(species) do
     Repo.preload(species, [:homeworld, :people, :films])

lib/swapi/starships.ex

@@ -8,7 +8,7 @@ defmodule SWAPI.Starships do
   alias SWAPI.Schemas.Transport
 
   import Ecto.Query, warn: false
-  import SWAPI.Util
+  import SWAPI.Pagination
 
   def preload_all(starship) do
     Repo.preload(starship, [:transport, :films, :pilots])

lib/swapi/util.ex

@@ -8,7 +8,7 @@ defmodule SWAPI.Vehicles do
   alias SWAPI.Schemas.Vehicle
 
   import Ecto.Query, warn: false
-  import SWAPI.Util
+  import SWAPI.Pagination
 
   def preload_all(vehicle) do
     Repo.preload(vehicle, [:transport, :films, :pilots])

lib/swapi/vehicles.ex

@@ -2,6 +2,7 @@ defmodule SWAPIWeb.FilmController do
   use SWAPIWeb, :controller
   use OpenApiSpex.ControllerSpecs
 
+  alias OpenApiSpex.Schema
   alias SWAPI.Films
 
   import SWAPIWeb.Util
@@ -19,7 +20,32 @@ defmodule SWAPIWeb.FilmController do
           "One or more search terms, which should be whitespace and/or comma separated. If multiple search terms are used then objects will be returned in the list only if all the provided terms are matched. Searches may contain quoted phrases with spaces, each phrase is considered as a single search term.",
         type: :string
       ],
-      page: [in: :query, description: "Page number", type: :integer]
+      page: [
+        in: :query,
+        description: "Page number. Cannot be used together with `offset`.",
+        schema: %Schema{
+          type: :integer,
+          minimum: 1,
+          default: 1
+        }
+      ],
+      offset: [
+        in: :query,
+        description: "Offset of the first item. Cannot be used together with `page`.",
+        schema: %Schema{
+          type: :integer,
+          minimum: 0
+        }
+      ],
+      limit: [
+        in: :query,
+        description: "Maximum number of items to return in the response.",
+        schema: %Schema{
+          type: :integer,
+          minimum: 1,
+          default: 10
+        }
+      ]
     ],
     responses: [
       ok: {"List of films", "application/json", SWAPIWeb.Schemas.FilmList}