add if_not_exists option to add_value_to_type (#13)

lib/ecto_enum_migration.ex

@@ -141,7 +141,7 @@ defmodule EctoEnumMigration do
     def up do
       add_value_to_type(:status, :finished)
     end
-    
+
     def down do
     end
   end
@@ -168,6 +168,12 @@ defmodule EctoEnumMigration do
   add_value_to_type(:status, :finished, after: :started)
   ```
 
+  Can specify to only add value if not exists with the `:if_not_exists` option
+
+  ```elixir
+  add_value_to_type(:status, :finished, if_not_exists: true)
+  ```
+
   """
   @spec add_value_to_type(name :: atom(), value :: atom(), opts :: Keyword.t()) ::
           :ok | no_return()
@@ -177,6 +183,7 @@ defmodule EctoEnumMigration do
       "ALTER TYPE",
       type_name(name, opts),
       "ADD VALUE",
+      if_not_exists_sql(opts),
       to_value(value),
       before_after(opts),
       ";"
@@ -267,6 +274,14 @@ defmodule EctoEnumMigration do
     end
   end
 
+  defp if_not_exists_sql(opts) do
+    if Keyword.get(opts, :if_not_exists, false) do
+      "IF NOT EXISTS"
+    else
+      []
+    end
+  end
+
   defp execute_query(terms) do
     terms
     |> Enum.reject(&(is_nil(&1) || &1 == []))

test/ecto_enum_migration_test.exs

@@ -104,6 +104,16 @@ defmodule EctoEnumMigrationTest do
     end
   end
 
+  defmodule AddValueToTypeIfNotExistsMigration do
+    use Ecto.Migration
+    import EctoEnumMigration
+    @disable_ddl_transaction true
+
+    def change do
+      add_value_to_type(:status, :finished, if_not_exists: true)
+    end
+  end
+
   defmodule AddValueToTypeWithCustomSchemaMigration do
     use Ecto.Migration
     import EctoEnumMigration
@@ -296,6 +306,24 @@ defmodule EctoEnumMigrationTest do
       end
     end
 
+    test "supports if not exists option" do
+      create_version = version_number()
+      add_value_version = version_number()
+      add_value_version_again = version_number()
+
+      :ok = up(create_version, CreateTypeMigration)
+      :ok = up(add_value_version, AddValueToTypeIfNotExistsMigration)
+      :ok = up(add_value_version_again, AddValueToTypeIfNotExistsMigration)
+
+      assert current_types() == %{
+               "public.status" => ["registered", "active", "inactive", "archived", "finished"]
+             }
+
+      assert_raise Ecto.MigrationError, ~r/cannot reverse migration command/, fn ->
+        :ok = down(add_value_version, AddValueToTypeIfNotExistsMigration)
+      end
+    end
+
     test "supports before option" do
       create_version = version_number()
       add_value_version = version_number()