tom throw if no conn. configuration registered

tom/include/tom/application.hpp

@@ -244,6 +244,8 @@ namespace Concerns
         /*! Get database connection resolver. */
         std::shared_ptr<ConnectionResolverInterface> resolver() const noexcept;
 
+        /*! Throw if no connection configuration is registered. */
+        void throwIfNoConnectionConfig() const;
         /*! Throw if a default connection is empty. */
         void throwIfEmptyDefaultConnection() const;
 

tom/src/tom/application.cpp

@@ -159,6 +159,8 @@ Application::Application(int &argc, char **argv, std::shared_ptr<DatabaseManager
 
 int Application::run()
 {
+    // Throw if no database connection configuration is registered
+    throwIfNoConnectionConfig();
     // Default database connection is required if exactly one connection is registered
     throwIfEmptyDefaultConnection();
 
@@ -653,6 +655,18 @@ std::shared_ptr<ConnectionResolverInterface> Application::resolver() const noexc
     return std::dynamic_pointer_cast<ConnectionResolverInterface>(m_db);
 }
 
+void Application::throwIfNoConnectionConfig() const
+{
+    // Nothing to do, some database connection configuration/s are already registered
+    if (m_db->originalConfigsSize() > 0)
+        return;
+
+    throw Exceptions::RuntimeError(
+                "No connection configuration is registered, please add at least one "
+                "database configuration to the DatabaseManager (eg. using "
+                "DB::create()).");
+}
+
 void Application::throwIfEmptyDefaultConnection() const
 {
     // Nothing to do, default connection is defined or more connections is registered