insert query builder has many to many progress

include/matador/object/collection.hpp

@@ -8,9 +8,9 @@ namespace matador::object {
 template < class Type >
 class collection {
 public:
-  using value_type = Type;
-  using iterator = typename std::vector<value_type>::iterator;
-  using const_iterator = typename std::vector<value_type>::const_iterator;
+  using value_type = typename collection_proxy<Type>::value_type;
+  using iterator = typename collection_proxy<Type>::iterator;
+  using const_iterator = typename collection_proxy<Type>::const_iterator;
 
   collection()
   : proxy_(std::make_shared<collection_proxy<Type>>()) {}

include/matador/object/collection_proxy.hpp

@@ -16,6 +16,10 @@ namespace matador::object {
 template<typename Type>
 class collection_proxy final {
 public:
+  using value_type = Type;
+  using iterator = typename std::vector<value_type>::iterator;
+  using const_iterator = typename std::vector<value_type>::const_iterator;
+
   collection_proxy() = default;
 
   // Lazy

include/matador/object/many_to_many_relation.hpp

@@ -15,6 +15,12 @@ public:
     many_to_many_relation(std::string local_name, std::string remote_name)
     : local_name_(std::move(local_name))
     , remote_name_(std::move(remote_name)) {}
+    many_to_many_relation(std::string local_name, std::string remote_name, const object_ptr<LocalType>& local, const object_ptr<ForeignType>& remote)
+    : local_name_(std::move(local_name))
+    , remote_name_(std::move(remote_name))
+    , local_(local)
+    , remote_(remote)
+    {}
 
     template<class Operator>
     void process(Operator &op) {