Code for step 2

lib/store_inventory.ex

@@ -1,18 +1,27 @@
 defmodule StoreInventory do
-  @moduledoc """
-  Documentation for `StoreInventory`.
-  """
+  alias StoreInventory.Item
 
-  @doc """
-  Hello world.
+  @repo Application.get_env(:store_inventory, :repo)
 
-  ## Examples
+  def insert_item(params) do
+    %Item{}
+    |> Item.changeset(params)
+    |> @repo.insert()
+  end
+
+  def all_items do
+    @repo.all(Item)
+  end
 
-      iex> StoreInventory.hello()
-      :world
+  def average_item_price do
+    {total, num_items} =
+      all_items()
+      |> Enum.reduce({0, 0}, fn %Item{} = item, {sum, count} ->
+        {sum + item.price, count + 1}
+      end)
 
-  """
-  def hello do
-    :world
+    if num_items == 0,
+      do: 0,
+      else: total / num_items
   end
 end

lib/store_inventory/item.ex

@@ -0,0 +1,26 @@
+defmodule StoreInventory.Item do
+  use Ecto.Schema
+
+  import Ecto.Changeset
+
+  alias __MODULE__
+
+  @all_fields [:name, :description, :price, :quantity]
+
+  schema "items" do
+    field(:name, :string)
+    field(:description, :string)
+    field(:price, :decimal)
+    field(:quantity, :integer)
+
+    timestamps()
+  end
+
+  def changeset(%Item{} = item, params \\ %{}) do
+    item
+    |> cast(params, @all_fields)
+    |> validate_required(@all_fields)
+    |> validate_number(:quantity, greater_than: 0)
+    |> validate_number(:price, greater_than: 0)
+  end
+end

priv/repo/migrations/20200601203937_items.exs

@@ -0,0 +1,14 @@
+defmodule StoreInventory.Repo.Migrations.Items do
+  use Ecto.Migration
+
+  def change do
+    create table("items") do
+      add(:name, :string)
+      add(:description, :string)
+      add(:price, :decimal)
+      add(:quantity, :integer)
+
+      timestamps()
+    end
+  end
+end