make poison optional

guides/Getting Started.md

@@ -10,13 +10,21 @@ Commanded can be installed from hex as follows.
     end
     ```
 
-2. Fetch mix dependencies:
+2. Optionally add `poison` to make `Commanded.Serialization.JsonSerializer` available:
+
+    ```elixir
+    def deps do
+      [{:poison, "~> 3.1 or ~> 4.0"}]
+    end
+    ```
+
+3. Fetch mix dependencies:
 
     ```console
     $ mix deps.get
     ```
 
-3. Configure one of the supported event stores by following the "Choosing an Event Store" guide.
+4. Configure one of the supported event stores by following the "Choosing an Event Store" guide.
 
 ## Starting the Commanded application
 

guides/Serialization.md

@@ -1,8 +1,16 @@
 # Serialization
 
-JSON serialization is used by default for event and snapshot data.
+JSON serialization can be used for event and snapshot data.
 
-The included `Commanded.Serialization.JsonSerializer` module provides an extension point to allow additional decoding of the deserialized value. This can be used for parsing data into valid structures, such as date/time parsing from a string.
+To enable JSON serialization with the included `Commanded.Serialization.JsonSerializer` module add `poison` to your deps
+
+    ```elixir
+    def deps do
+      [{:poison, "~> 3.1 or ~> 4.0"}]
+    end
+    ```
+
+The `Commanded.Serialization.JsonSerializer` module provides an extension point to allow additional decoding of the deserialized value. This can be used for parsing data into valid structures, such as date/time parsing from a string.
 
 The example event below has an implementation of the `Commanded.Serialization.JsonDecoder` protocol to parse the date into a `NaiveDateTime` struct.
 

lib/commanded/serialization/json_serializer.ex

@@ -1,30 +1,32 @@
-defmodule Commanded.Serialization.JsonSerializer do
-  @moduledoc """
-  A serializer that uses the JSON format.
-  """
+if Code.ensure_loaded?(Poison) do
+  defmodule Commanded.Serialization.JsonSerializer do
+    @moduledoc """
+    A serializer that uses the JSON format.
+    """
 
-  alias Commanded.EventStore.TypeProvider
-  alias Commanded.Serialization.JsonDecoder
+    alias Commanded.EventStore.TypeProvider
+    alias Commanded.Serialization.JsonDecoder
 
-  @doc """
-  Serialize given term to JSON binary data.
-  """
-  def serialize(term) do
-    Poison.encode!(term)
-  end
-
-  @doc """
-  Deserialize given JSON binary data to the expected type.
-  """
-  def deserialize(binary, config \\ [])
-  def deserialize(binary, config) do
-    type = case Keyword.get(config, :type) do
-      nil -> nil
-      type -> TypeProvider.to_struct(type)
+    @doc """
+    Serialize given term to JSON binary data.
+    """
+    def serialize(term) do
+      Poison.encode!(term)
     end
 
-    binary
-    |> Poison.decode!(as: type)
-    |> JsonDecoder.decode()
+    @doc """
+    Deserialize given JSON binary data to the expected type.
+    """
+    def deserialize(binary, config \\ [])
+    def deserialize(binary, config) do
+      type = case Keyword.get(config, :type) do
+        nil -> nil
+        type -> TypeProvider.to_struct(type)
+      end
+
+      binary
+      |> Poison.decode!(as: type)
+      |> JsonDecoder.decode()
+    end
   end
 end

mix.exs

@@ -50,7 +50,7 @@ defmodule Commanded.Mixfile do
   defp deps do
     [
       {:elixir_uuid, "~> 1.2"},
-      {:poison, "~> 3.1 or ~> 4.0"},
+      {:poison, "~> 3.1 or ~> 4.0", optional: true},
 
       # Build & test tools
       {:dialyxir, "~> 0.5", only: :dev, runtime: false},