added any type visitor and converter

backends/sqlite/include/sqlite_connection.hpp

@@ -33,6 +33,8 @@ public:
 
   sql::record describe(const std::string& table) override;
 
+  bool exists(const std::string &table_name) override;
+
 private:
   static int parse_result(void* param, int column_count, char** values, char** columns);
 

backends/sqlite/src/sqlite_connection.cpp

@@ -153,14 +153,27 @@ sql::record sqlite_connection::describe(const std::string& table)
       options = utils::constraints::NOT_NULL;
     }
     // f.default_value(res->column(4));
-    //    end = nullptr;
-    //    f.is_primary_key(strtoul(res->column(3), &end, 10) == 0);
     prototype.append({name, type, {options}});
   }
 
   return std::move(prototype);
 }
 
+bool sqlite_connection::exists(const std::string &table_name)
+{
+  const auto result = fetch("SELECT COUNT(*) FROM sqlite_master WHERE type='table' AND tbl_name='" + table_name + "' LIMIT 1");
+
+  if (!result->fetch()) {
+    // Todo: throw an exception?
+    return false;
+  }
+
+  int v{};
+  result->read_value(nullptr, 0, v);
+
+  return v == 1;
+}
+
 }
 
 extern "C"