added timestamp code, support columns for group by and order by and tested load has-many eager code

include/matador/object/attribute.hpp

@@ -52,6 +52,7 @@ public:
   [[nodiscard]] bool is_varchar() const;
   [[nodiscard]] bool is_date() const;
   [[nodiscard]] bool is_time() const;
+  [[nodiscard]] bool is_timestamp() const;
   [[nodiscard]] bool is_blob() const;
   [[nodiscard]] bool is_null() const;
 

include/matador/object/collection.hpp

@@ -8,11 +8,13 @@ namespace matador::object {
 template < class Type >
 class collection {
 public:
-    using value_type = Type;
+  using value_type = Type;
 
+  void push_back(const Type& value) { data_.push_back(value); }
+
+  [[nodiscard]] size_t size() const { return data_.size(); }
 private:
   std::vector<Type> data_;
-
 };
 
 }