has many fetch with join

include/matador/sql/field.hpp

@@ -8,8 +8,17 @@
 #include <optional>
 #include <string>
 
+namespace matador::utils {
+enum class constraints : unsigned char;
+}
 namespace matador::sql {
 
+enum struct field_type {
+    Attribute,
+    PrimaryKey,
+    ForeignKey
+};
+
 /**
  *
  */
@@ -17,11 +26,12 @@ class field {
 public:
   explicit field(std::string name);
   template<typename Type>
-  field(std::string name, Type value, const size_t size = 0, const int index = -1)
+  field(std::string name, Type value, const field_type type = field_type::Attribute, const size_t size = 0, const int index = -1)
   : name_(std::move(name))
+  , type_(type)
   , index_(index)
   , value_(value, size) {}
-  field(std::string name, utils::basic_type dt, size_t size = 0, int index = -1);
+  field(std::string name, utils::basic_type dt, field_type type = field_type::Attribute, size_t size = 0, int index = -1);
   field(const field &x) = default;
   field& operator=(const field &x) = default;
   field(field &&x) noexcept;
@@ -35,6 +45,7 @@ public:
   }
 
   [[nodiscard]] const std::string& name() const;
+  [[nodiscard]] field_type type() const;
   [[nodiscard]] size_t size() const;
   [[nodiscard]] int index() const;
 
@@ -53,18 +64,25 @@ public:
   [[nodiscard]] bool is_blob() const;
   [[nodiscard]] bool is_null() const;
 
+  [[nodiscard]] bool is_primary_key() const;
+  [[nodiscard]] bool is_foreign_key() const;
+  [[nodiscard]] bool is_attribute() const;
+
   friend std::ostream& operator<<(std::ostream &out, const field &col);
 
 private:
+  static utils::constraints determine_constraint(field_type type);
+
   template<class Operator>
   void process(Operator &op) {
-    op.on_attribute(name_.c_str(), value_, value_.size());
+    op.on_attribute(name_.c_str(), value_, { value_.size(), determine_constraint(type_) } );
   }
 
 private:
   friend class record;
 
   std::string name_;
+  field_type type_{field_type::Attribute};
   int index_{-1};
 
   utils::value value_;