refactor: unify preload_defaults functions

Provide a global `Repo.preload_defaults` to load default preloads for a
given module, instead of using a distinct function for each one.

`Repo.preload_defaults`'s logic is to make modules define their own
`default_preloads/0` function, and use its return value as
`Repo.preload/3`'s second parameter.

`Repo.preload_defaults_in_result` is provided for ease of use after
a fetch/update/insert method.

Signed-off-by: Francesco Noacco <francesco.noacco@secomind.com>

backend/lib/edgehog/base_images.ex

@@ -38,16 +38,6 @@ defmodule Edgehog.BaseImages do
                     BucketStorage
                   )
 
-  @doc """
-  Preloads the default associations for a Base Image Collection (or a list of base image collections)
-  """
-  def preload_defaults_for_base_image_collection(collection_or_collections) do
-    Repo.preload(collection_or_collections,
-      base_images: [],
-      system_model: [:hardware_type, :part_numbers]
-    )
-  end
-
   @doc """
   Returns the list of base_image_collections.
 
@@ -59,7 +49,7 @@ defmodule Edgehog.BaseImages do
   """
   def list_base_image_collections do
     Repo.all(BaseImageCollection)
-    |> preload_defaults_for_base_image_collection()
+    |> Repo.preload_defaults()
   end
 
   @doc """
@@ -77,9 +67,8 @@ defmodule Edgehog.BaseImages do
 
   """
   def fetch_base_image_collection(id) do
-    with {:ok, base_image_collection} <- Repo.fetch(BaseImageCollection, id) do
-      {:ok, preload_defaults_for_base_image_collection(base_image_collection)}
-    end
+    Repo.fetch(BaseImageCollection, id)
+    |> Repo.preload_defaults_in_result()
   end
 
   @doc """
@@ -99,9 +88,8 @@ defmodule Edgehog.BaseImages do
       %BaseImageCollection{system_model_id: system_model.id}
       |> BaseImageCollection.changeset(attrs)
 
-    with {:ok, base_image_collection} <- Repo.insert(changeset) do
-      {:ok, preload_defaults_for_base_image_collection(base_image_collection)}
-    end
+    Repo.insert(changeset)
+    |> Repo.preload_defaults_in_result()
   end
 
   @doc """
@@ -119,9 +107,8 @@ defmodule Edgehog.BaseImages do
   def update_base_image_collection(%BaseImageCollection{} = base_image_collection, attrs) do
     changeset = BaseImageCollection.changeset(base_image_collection, attrs)
 
-    with {:ok, base_image_collection} <- Repo.update(changeset) do
-      {:ok, preload_defaults_for_base_image_collection(base_image_collection)}
-    end
+    Repo.update(changeset)
+    |> Repo.preload_defaults_in_result()
   end
 
   @doc """
@@ -137,9 +124,8 @@ defmodule Edgehog.BaseImages do
 
   """
   def delete_base_image_collection(%BaseImageCollection{} = base_image_collection) do
-    with {:ok, base_image_collection} <- Repo.delete(base_image_collection) do
-      {:ok, preload_defaults_for_base_image_collection(base_image_collection)}
-    end
+    Repo.delete(base_image_collection)
+    |> Repo.preload_defaults_in_result()
   end
 
   @doc """
@@ -155,17 +141,6 @@ defmodule Edgehog.BaseImages do
     BaseImageCollection.changeset(base_image_collection, attrs)
   end
 
-  @doc """
-  Preloads the default associations for a Base Image (or a list of base images)
-  """
-  def preload_defaults_for_base_image(image_or_images) do
-    Repo.preload(image_or_images,
-      base_image_collection: [
-        system_model: [:hardware_type, :part_numbers]
-      ]
-    )
-  end
-
   @doc """
   Returns the list of base_images.
 
@@ -177,7 +152,7 @@ defmodule Edgehog.BaseImages do
   """
   def list_base_images do
     Repo.all(BaseImage)
-    |> preload_defaults_for_base_image()
+    |> Repo.preload_defaults()
   end
 
   @doc """
@@ -192,7 +167,7 @@ defmodule Edgehog.BaseImages do
   def list_base_images_for_collection(%BaseImageCollection{} = base_image_collection) do
     Ecto.assoc(base_image_collection, :base_images)
     |> Repo.all()
-    |> preload_defaults_for_base_image()
+    |> Repo.preload_defaults()
   end
 
   @doc """
@@ -210,9 +185,8 @@ defmodule Edgehog.BaseImages do
 
   """
   def fetch_base_image(id) do
-    with {:ok, base_image} <- Repo.fetch(BaseImage, id) do
-      {:ok, preload_defaults_for_base_image(base_image)}
-    end
+    Repo.fetch(BaseImage, id)
+    |> Repo.preload_defaults_in_result()
   end
 
   @doc """
@@ -245,7 +219,7 @@ defmodule Edgehog.BaseImages do
     |> Repo.transaction()
     |> case do
       {:ok, %{base_image: base_image}} ->
-        {:ok, preload_defaults_for_base_image(base_image)}
+        {:ok, Repo.preload_defaults(base_image)}
 
       {:error, _failed_operation, failed_value, _changes_so_far} ->
         {:error, failed_value}
@@ -267,9 +241,8 @@ defmodule Edgehog.BaseImages do
   def update_base_image(%BaseImage{} = base_image, attrs) do
     changeset = BaseImage.update_changeset(base_image, attrs)
 
-    with {:ok, base_image} <- Repo.update(changeset) do
-      {:ok, preload_defaults_for_base_image(base_image)}
-    end
+    Repo.update(changeset)
+    |> Repo.preload_defaults_in_result()
   end
 
   @doc """
@@ -296,7 +269,7 @@ defmodule Edgehog.BaseImages do
     |> Repo.transaction()
     |> case do
       {:ok, %{base_image: base_image}} ->
-        {:ok, preload_defaults_for_base_image(base_image)}
+        {:ok, Repo.preload_defaults(base_image)}
 
       {:error, _failed_operation, failed_value, _changes_so_far} ->
         {:error, failed_value}

backend/lib/edgehog/base_images/base_image.ex

@@ -80,4 +80,12 @@ defmodule Edgehog.BaseImages.BaseImage do
         [{field, "is not a valid version requirement"}]
     end
   end
+
+  def default_preloads do
+    [
+      base_image_collection: [
+        system_model: [:hardware_type, :part_numbers]
+      ]
+    ]
+  end
 end

backend/lib/edgehog/base_images/base_image_collection.ex

@@ -49,4 +49,8 @@ defmodule Edgehog.BaseImages.BaseImageCollection do
         "should start with a lower case ASCII letter and only contain lower case ASCII letters, digits and -"
     )
   end
+
+  def default_preloads do
+    [base_images: [], system_model: [:hardware_type, :part_numbers]]
+  end
 end

backend/lib/edgehog/devices.ex

@@ -51,7 +51,7 @@ defmodule Edgehog.Devices do
   """
   def get_device!(id) do
     Repo.get!(Device, id)
-    |> preload_defaults_for_device()
+    |> Repo.preload_defaults()
   end
 
   @doc """
@@ -67,18 +67,7 @@ defmodule Edgehog.Devices do
     filters
     |> Enum.reduce(Device, &filter_with/2)
     |> Repo.all()
-    |> preload_defaults_for_device()
-  end
-
-  @doc """
-  Preloads the default associations for an Edgehog Device (or a list of devices)
-  """
-  def preload_defaults_for_device(device_or_devices) do
-    Repo.preload(device_or_devices,
-      tags: [],
-      custom_attributes: [],
-      system_model: [:hardware_type, :part_numbers]
-    )
+    |> Repo.preload_defaults()
   end
 
   defp filter_with({:online, online}, query) do
@@ -220,7 +209,7 @@ defmodule Edgehog.Devices do
     |> Repo.transaction()
     |> case do
       {:ok, %{update_device: device}} ->
-        {:ok, preload_defaults_for_device(device)}
+        {:ok, Repo.preload_defaults(device)}
 
       {:error, _failed_operation, failed_value, _progress_so_far} ->
         {:error, failed_value}

backend/lib/edgehog/devices/device.ex

@@ -61,4 +61,8 @@ defmodule Edgehog.Devices.Device do
       with: &Labeling.DeviceAttribute.custom_attribute_changeset/2
     )
   end
+
+  def default_preloads do
+    [tags: [], custom_attributes: [], system_model: [:hardware_type, :part_numbers]]
+  end
 end

backend/lib/edgehog/groups.ex

@@ -1,7 +1,7 @@
 #
 # This file is part of Edgehog.
 #
-# Copyright 2022 SECO Mind Srl
+# Copyright 2022-2023 SECO Mind Srl
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -24,7 +24,6 @@ defmodule Edgehog.Groups do
   """
 
   import Ecto.Query, warn: false
-  alias Edgehog.Devices
   alias Edgehog.Groups.DeviceGroup
   alias Edgehog.Repo
   alias Edgehog.Selector
@@ -57,7 +56,7 @@ defmodule Edgehog.Groups do
     {:ok, device_query} = Selector.to_ecto_query(device_group.selector)
 
     Repo.all(device_query)
-    |> Devices.preload_defaults_for_device()
+    |> Repo.preload_defaults()
   end
 
   @doc """

backend/lib/edgehog/repo.ex

@@ -1,7 +1,7 @@
 #
 # This file is part of Edgehog.
 #
-# Copyright 2021 SECO Mind Srl
+# Copyright 2021-2023 SECO Mind Srl
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -71,4 +71,37 @@ defmodule Edgehog.Repo do
   def default_options(_operation) do
     [tenant_id: get_tenant_id()]
   end
+
+  @doc """
+  Preloads default relationships for the given struct(s), defined by a `default_preloads/0` function
+  in the struct's module.
+  """
+  def preload_defaults(struct_or_structs_or_nil, opts \\ [])
+
+  def preload_defaults(struct_or_structs_or_nil, opts)
+      when is_struct(struct_or_structs_or_nil) or is_nil(struct_or_structs_or_nil) do
+    do_preload_defaults(struct_or_structs_or_nil, struct_or_structs_or_nil, opts)
+  end
+
+  def preload_defaults(struct_or_structs_or_nil, opts)
+      when is_list(struct_or_structs_or_nil) do
+    non_nil_item = Enum.find(struct_or_structs_or_nil, & &1)
+    do_preload_defaults(non_nil_item, struct_or_structs_or_nil, opts)
+  end
+
+  defp do_preload_defaults(nil = _reference_item, struct_or_structs_or_nil, _opts) do
+    struct_or_structs_or_nil
+  end
+
+  defp do_preload_defaults(reference_item, struct_or_structs_or_nil, opts) do
+    module = reference_item.__struct__
+    preloads = module.default_preloads()
+    preload(struct_or_structs_or_nil, preloads, opts)
+  end
+
+  def preload_defaults_in_result(result, opts \\ []) do
+    with {:ok, item} <- result do
+      {:ok, preload_defaults(item, opts)}
+    end
+  end
 end