Add Exqlite.TypeExtensions to allow more types to be stored in the database

README.md

@@ -46,12 +46,17 @@ end
 ### Runtime Configuration
 
 ```elixir
-config :exqlite, default_chunk_size: 100
+config :exqlite,
+    default_chunk_size: 100,
+    type_extensions: [MyApp.TypeExtension]
 ```
 
 * `default_chunk_size` - The chunk size that is used when multi-stepping when
   not specifying the chunk size explicitly.
-
+* `type_extensions`: An optional list of modules that implement the
+  Exqlite.TypeExtension behaviour, allowing types beyond the default set that
+  can be stored and retrieved from the database.
+
 ### Compile-time Configuration
 
 In `config/config.exs`,

lib/exqlite/sqlite3.ex

@@ -481,5 +481,27 @@ defmodule Exqlite.Sqlite3 do
     raise ArgumentError, "#{inspect(datetime)} is not in UTC"
   end
 
-  defp convert(val), do: val
+  defp convert(val) do
+    convert_with_type_extensions(type_extensions(), val)
+  end
+
+  defp convert_with_type_extensions([], val), do: val
+
+  defp convert_with_type_extensions([extension | other_extensions], val) do
+    case extension.convert(val) do
+      nil ->
+        convert_with_type_extensions(other_extensions, val)
+
+      {:ok, converted} ->
+        converted
+
+      {:error, reason} ->
+        raise ArgumentError,
+              "Failed conversion by TypeExtension #{extension}: #{inspect(val)}. Reason: #{inspect(reason)}."
+    end
+  end
+
+  defp type_extensions do
+    Application.get_env(:exqlite, :type_extensions, [])
+  end
 end

lib/exqlite/type_extension.ex

@@ -0,0 +1,14 @@
+defmodule Exqlite.TypeExtension do
+  @moduledoc """
+  A behaviour that defines the API for extensions providing custom data loaders and dumpers
+  for Ecto schemas.
+  """
+
+  @doc """
+  Takes a value and convers it to data suitable for storage in the database.
+
+  Returns a tagged :ok/:error tuple. If the value is not convertable by this
+  extension, returns nil.
+  """
+  @callback convert(value :: term) :: {:ok, term} | {:error, reason :: term} | nil
+end