Extract setting prefix to a method

We may need to access the setting key prefix in the future, so it's
better to have it in a method to avoid duplication

app/models/setting.rb

@@ -3,8 +3,11 @@ class Setting < ApplicationRecord
 
   default_scope { order(id: :asc) }
 
+  def prefix
+    key.split(".").first
+  end
+
   def type
-    prefix = key.split(".").first
     if %w[feature process proposals map html homepage].include? prefix
       prefix
     else

spec/models/setting_spec.rb

@@ -17,6 +17,16 @@ describe Setting do
     expect(described_class.where(key: "official_level_1_name", value: "Stormtrooper")).to exist
   end
 
+  describe "#prefix" do
+    it "returns the prefix of its key" do
+      expect(Setting.create(key: "prefix.key_name").prefix).to eq "prefix"
+    end
+
+    it "returns the whole key for a non prefixed key" do
+      expect(Setting.create(key: "key_name").prefix).to eq "key_name"
+    end
+  end
+
   describe "#type" do
     it "returns the key prefix for 'process' settings" do
       process_setting = Setting.create(key: "process.whatever")