added sequence_pk_generator implementation

include/matador/query/abstract_pk_generator.hpp

@@ -0,0 +1,19 @@
+#ifndef MATADOR_ABSTRACT_PK_GENERATOR_HPP
+#define MATADOR_ABSTRACT_PK_GENERATOR_HPP
+
+#include "matador/utils/error.hpp"
+#include "matador/utils/result.hpp"
+
+#include <cstdint>
+
+namespace matador::sql {
+class executor;
+}
+namespace matador::query {
+class abstract_pk_generator {
+public:
+  virtual ~abstract_pk_generator() = default;
+  virtual utils::result<int64_t, utils::error> next_id(const sql::executor& exec) = 0;
+};
+}
+#endif //MATADOR_ABSTRACT_PK_GENERATOR_HPP

include/matador/query/intermediates/fetchable_query.hpp

@@ -61,8 +61,7 @@ public:
   [[nodiscard]] utils::result<std::optional<sql::record>, utils::error> fetch_one(const sql::executor &exec) const;
 
   template<typename Type>
-  utils::result<std::optional<Type>, utils::error> fetch_value(const sql::executor &exec)
-  {
+  utils::result<std::optional<Type>, utils::error> fetch_value(const sql::executor &exec) {
     const auto result = fetch_one(exec);
     if (!result.is_ok()) {
       return utils::failure(result.err());

include/matador/query/sequence_pk_generator.hpp

@@ -0,0 +1,20 @@
+#ifndef MATADOR_SEQUENCE_PK_GENERATOR_H
+#define MATADOR_SEQUENCE_PK_GENERATOR_H
+
+#include "matador/query/abstract_pk_generator.hpp"
+#include "matador/query/intermediates/fetchable_query.hpp"
+
+#include <string>
+
+namespace matador::query {
+class sequence_pk_generator : public abstract_pk_generator {
+public:
+    explicit sequence_pk_generator(const std::string& sequence_name);
+
+    utils::result<int64_t, utils::error> next_id(const sql::executor& exec) override;
+
+private:
+    fetchable_query query_;
+};
+}
+#endif //MATADOR_SEQUENCE_PK_GENERATOR_H