diff --git a/README.md b/README.md
index 119da3d..24e9f84 100644
--- a/README.md
+++ b/README.md
@@ -80,10 +80,12 @@ defmodule MyApp.Channel.SMS do
 end
 ```
 
-The `:types` option for the `PolymorphicEmbed` custom type contains a keyword list mapping an atom representing the type
-(in this example `:email` and `:sms`) with the corresponding embedded schema module.
+The `:types` option for the `PolymorphicEmbed` custom type either contains a keyword list 
+mapping an atom representing the type (in this example `:email` and `:sms`) with the corresponding 
+embedded schema module, or specifies a function that can be used to map any type value into
+a corresponding schema module.
 
-There are two strategies to detect the right embedded schema to use:
+There are four strategies to detect the right embedded schema to use:
 
 1.
 ```elixir
@@ -107,6 +109,50 @@ parameter is then no longer required.
 Note that you may still include a `__type__` parameter that will take precedence over this strategy (this could still be
 useful if you need to store incomplete data, which might not allow identifying the type).
 
+3.
+```elixir
+# Converts an arbritary type atom or string key to a schema module, e.g. "email" to MyApp.Channel.Email
+def lookup_type(key, :module) do
+  case to_string(key) do
+    "sms" -> MyApp.Channel.SMS
+    _other -> Module.safe_concat(["MyApp.Channel", String.capitalize(key)])
+  end
+end
+
+# Reverse lookup, converts the module to the appropriate type
+def lookup_type(key, :type) do
+  Module.split(key) 
+  |> List.last() 
+  |> String.downcase() 
+  |> String.to_atom()
+end
+
+
+types: &MyModule.lookup_type/2
+```
+
+If you specify `types: &MyModule.lookup_type/2` with the format `&Mod.fun/arity` as in the example above,
+you supply a reference to a 2-arity function that converts both ways between types and modules.
+The first argument to the function is the key to be converted, and the second argument is 
+either `:module` to convert from a type to a module, or `:key` to convert from a module to the type.
+This allows you to embed arbitrary schemas without having to list
+them all explicitly. The function should return an atom, not a string value.
+
+4.
+```elixir
+types: :by_module
+```
+
+If you specify `types: :by_module`, the `"__type__"` (or `:__type__`) parameter should contain the fully qualified
+and reachable module name of the embedded schema, such as "MyApp.Channel.Email". This is equivalent to specifying
+`types: &MyModule.lookup_type/2`, where `lookup_type` was defined as:
+
+```elixir
+def lookup_type(key, :module), do: Module.safe_concat([to_string(key)])
+def lookup_type(key, :type), do: key
+```
+
+
 ### Options
 
 * `:types` - discussed above.
diff --git a/lib/polymorphic_embed.ex b/lib/polymorphic_embed.ex
index 40ef17f..7782f65 100644
--- a/lib/polymorphic_embed.ex
+++ b/lib/polymorphic_embed.ex
@@ -7,25 +7,37 @@ defmodule PolymorphicEmbed do
   @impl true
   def init(opts) do
     metadata =
-      Keyword.fetch!(opts, :types)
-      |> Enum.map(fn
-        {type_name, type_opts} when is_list(type_opts) ->
-          module = Keyword.fetch!(type_opts, :module)
-          identify_by_fields = Keyword.fetch!(type_opts, :identify_by_fields)
-
-          %{
-            type: type_name |> to_string(),
-            module: module,
-            identify_by_fields: identify_by_fields |> Enum.map(&to_string/1)
-          }
-
-        {type_name, module} ->
-          %{
-            type: type_name |> to_string(),
-            module: module,
-            identify_by_fields: []
-          }
-      end)
+      case Keyword.get(opts, :types) do
+        types when is_list(types) ->
+          types
+          |> Enum.map(fn
+            {type_name, type_opts} when is_list(type_opts) ->
+              module = Keyword.fetch!(type_opts, :module)
+              identify_by_fields = Keyword.fetch!(type_opts, :identify_by_fields)
+
+              %{
+                type: type_name |> to_string(),
+                module: module,
+                identify_by_fields: identify_by_fields |> Enum.map(&to_string/1)
+              }
+
+            {type_name, module} ->
+              %{
+                type: type_name |> to_string(),
+                module: module,
+                identify_by_fields: []
+              }
+          end)
+
+        :by_module ->
+          %{lookup_type_fun: :by_module}
+
+        type_fun when is_function(type_fun, 2) ->
+          %{lookup_type_fun: type_fun}
+
+        _ ->
+          raise ArgumentError, ":types option must be list or :by_module or 2-arity function"
+      end
 
     %{
       metadata: metadata,
@@ -186,7 +198,7 @@ defmodule PolymorphicEmbed do
   defp do_get_polymorphic_module(%{"__type__" => type}, metadata),
     do: do_get_polymorphic_module(type, metadata)
 
-  defp do_get_polymorphic_module(%{} = attrs, metadata) do
+  defp do_get_polymorphic_module(%{} = attrs, metadata) when is_list(metadata) do
     # check if one list is contained in another
     # Enum.count(contained -- container) == 0
     # contained -- container == []
@@ -196,7 +208,7 @@ defmodule PolymorphicEmbed do
     |> (&(&1 && Map.fetch!(&1, :module))).()
   end
 
-  defp do_get_polymorphic_module(type, metadata) do
+  defp do_get_polymorphic_module(type, metadata) when is_list(metadata) do
     type = to_string(type)
 
     metadata
@@ -204,6 +216,17 @@ defmodule PolymorphicEmbed do
     |> (&(&1 && Map.fetch!(&1, :module))).()
   end
 
+  defp do_get_polymorphic_module(type, %{lookup_type_fun: :by_module}) do
+    type = to_string(type)
+
+    Module.safe_concat([type])
+  end
+
+  defp do_get_polymorphic_module(type, %{lookup_type_fun: type_fun})
+       when is_function(type_fun) do
+    type_fun.(type, :module)
+  end
+
   def get_polymorphic_type(schema, field, module_or_struct) do
     %{metadata: metadata} = get_options(schema, field)
     do_get_polymorphic_type(module_or_struct, metadata)
@@ -212,13 +235,21 @@ defmodule PolymorphicEmbed do
   defp do_get_polymorphic_type(%module{}, metadata),
     do: do_get_polymorphic_type(module, metadata)
 
-  defp do_get_polymorphic_type(module, metadata) do
+  defp do_get_polymorphic_type(module, metadata) when is_list(metadata) do
     metadata
     |> Enum.find(&(module == &1.module))
     |> Map.fetch!(:type)
     |> String.to_atom()
   end
 
+  defp do_get_polymorphic_type(module, %{lookup_type_fun: :by_module}) do
+    module
+  end
+
+  defp do_get_polymorphic_type(module, %{lookup_type_fun: type_fun}) when is_function(type_fun) do
+    type_fun.(module, :type)
+  end
+
   defp get_options(schema, field) do
     try do
       schema.__schema__(:type, field)
diff --git a/test/polymorphic_embed_test.exs b/test/polymorphic_embed_test.exs
index d6178cf..beca793 100644
--- a/test/polymorphic_embed_test.exs
+++ b/test/polymorphic_embed_test.exs
@@ -64,6 +64,54 @@ defmodule PolymorphicEmbedTest do
     assert ~U[2020-05-28 07:27:05Z] == hd(reminder.channel.attempts).date
   end
 
+  test "with :by_module" do
+    sms_reminder_attrs = %{
+      date: ~U[2020-05-28 02:57:19Z],
+      text: "This reminder has an SMS source",
+      source: %{
+        __type__: "PolymorphicEmbed.Channel.SMS",
+        number: "02/807.05.53",
+        result: %{success: true},
+        attempts: [
+          %{
+            date: ~U[2020-05-28 07:27:05Z],
+            result: %{success: true}
+          },
+          %{
+            date: ~U[2020-05-29 07:27:05Z],
+            result: %{success: false}
+          },
+          %{
+            date: ~U[2020-05-30 07:27:05Z],
+            result: %{success: true}
+          }
+        ],
+        provider: %{
+          __type__: "twilio",
+          api_key: "foo"
+        }
+      }
+    }
+
+    insert_result =
+      %Reminder{source: %SMS{country_code: 1}}
+      |> Reminder.changeset(sms_reminder_attrs)
+      |> Repo.insert()
+
+    assert {:ok, %Reminder{}} = insert_result
+
+    reminder =
+      Reminder
+      |> QueryBuilder.where(text: "This reminder has an SMS source")
+      |> Repo.one()
+
+    assert SMS = reminder.source.__struct__
+    assert TwilioSMSProvider = reminder.source.provider.__struct__
+    assert SMSResult == reminder.source.result.__struct__
+    assert true == reminder.source.result.success
+    assert ~U[2020-05-28 07:27:05Z] == hd(reminder.source.attempts).date
+  end
+
   test "receive embed as struct" do
     reminder = %Reminder{
       date: ~U[2020-05-28 02:57:19Z],
@@ -100,6 +148,42 @@ defmodule PolymorphicEmbedTest do
     assert SMS = reminder.channel.__struct__
   end
 
+  test "receive :by_module embed as struct" do
+    reminder = %Reminder{
+      date: ~U[2020-05-28 02:57:19Z],
+      text: "This reminder has an SMS source",
+      source: %SMS{
+        provider: %TwilioSMSProvider{
+          api_key: "foo"
+        },
+        country_code: 1,
+        number: "02/807.05.53",
+        result: %SMSResult{success: true},
+        attempts: [
+          %SMSAttempts{
+            date: ~U[2020-05-28 07:27:05Z],
+            result: %SMSResult{success: true}
+          },
+          %SMSAttempts{
+            date: ~U[2020-05-28 07:27:05Z],
+            result: %SMSResult{success: true}
+          }
+        ]
+      }
+    }
+
+    reminder
+    |> Reminder.changeset(%{})
+    |> Repo.insert()
+
+    reminder =
+      Reminder
+      |> QueryBuilder.where(text: "This reminder has an SMS source")
+      |> Repo.one()
+
+    assert SMS = reminder.source.__struct__
+  end
+
   test "without __type__" do
     attrs = %{
       date: ~U[2020-05-28 02:57:19Z],
@@ -404,12 +488,36 @@ defmodule PolymorphicEmbedTest do
              }) ==
                :email
     end
+
+    test "returns the type for a :by_module type" do
+      assert PolymorphicEmbed.get_polymorphic_type(Reminder, :source, SMS) == SMS
+    end
+
+    test "returns the type for a lookup type" do
+      assert PolymorphicEmbed.get_polymorphic_type(Reminder, :reference, SMS) == :sms
+    end
   end
 
   describe "get_polymorphic_module/3" do
     test "returns the module for a type" do
       assert PolymorphicEmbed.get_polymorphic_module(Reminder, :channel, :sms) == SMS
     end
+
+    test "returns the module for a :by_module type with a string key" do
+      assert PolymorphicEmbed.get_polymorphic_module(
+               Reminder,
+               :source,
+               "PolymorphicEmbed.Channel.SMS"
+             ) == SMS
+    end
+
+    test "returns the module for a :by_module type with an atom key" do
+      assert PolymorphicEmbed.get_polymorphic_module(Reminder, :source, SMS) == SMS
+    end
+
+    test "returns the module for a lookup type" do
+      assert PolymorphicEmbed.get_polymorphic_module(Reminder, :reference, :sms) == SMS
+    end
   end
 
   defp safe_inputs_for(changeset, field, type, fun) do
diff --git a/test/support/migrations/20000101100000_add_source_field.exs b/test/support/migrations/20000101100000_add_source_field.exs
new file mode 100644
index 0000000..823a49a
--- /dev/null
+++ b/test/support/migrations/20000101100000_add_source_field.exs
@@ -0,0 +1,10 @@
+defmodule PolymorphicEmbed.AddSourceField do
+  use Ecto.Migration
+
+  def change do
+    alter table(:reminders) do
+      add(:source, :map)
+      add(:reference, :map)
+    end
+  end
+end
diff --git a/test/support/models/reminder.ex b/test/support/models/reminder.ex
index 3c0fab0..2a0d638 100644
--- a/test/support/models/reminder.ex
+++ b/test/support/models/reminder.ex
@@ -18,6 +18,9 @@ defmodule PolymorphicEmbed.Reminder do
       ]
     )
 
+    field(:source, PolymorphicEmbed, types: :by_module)
+    field(:reference, PolymorphicEmbed, types: &__MODULE__.lookup_type/2)
+
     timestamps()
   end
 
@@ -25,6 +28,17 @@ defmodule PolymorphicEmbed.Reminder do
     struct
     |> cast(values, [:date, :text])
     |> cast_polymorphic_embed(:channel)
+    |> cast_polymorphic_embed(:source)
     |> validate_required(:date)
   end
+
+  def lookup_type(key, :module) do
+    %{sms: PolymorphicEmbed.Channel.SMS, email: PolymorphicEmbed.Channel.Email}
+    |> Map.fetch!(key)
+  end
+
+  def lookup_type(key, :type) do
+    %{PolymorphicEmbed.Channel.SMS => :sms, PolymorphicEmbed.Channel.Email => :email}
+    |> Map.fetch!(key)
+  end
 end