added sequence_pk_generator implementation

source/orm/query/abstract_pk_generator.hpp

@@ -1,11 +0,0 @@
-#ifndef MATADOR_ABSTRACT_PK_GENERATOR_HPP
-#define MATADOR_ABSTRACT_PK_GENERATOR_HPP
-
-namespace matador::query {
-class abstract_pk_generator {
-public:
-  virtual ~abstract_pk_generator() = default;
-  virtual unsigned int generate() = 0;
-};
-}
-#endif //MATADOR_ABSTRACT_PK_GENERATOR_HPP

source/orm/query/sequence_pk_generator.cpp

@@ -0,0 +1,19 @@
+#include "matador/query/sequence_pk_generator.hpp"
+#include "matador/query/query.hpp"
+
+#include "matador/sql/error_code.hpp"
+
+namespace matador::query {
+sequence_pk_generator::sequence_pk_generator(const std::string& sequence_name)
+: query_(query::select().nextval(sequence_name)) {
+}
+
+utils::result<int64_t, utils::error> sequence_pk_generator::next_id(const sql::executor& exec) {
+    return query_.fetch_value<int64_t>(exec).and_then([](std::optional<int64_t> id) -> utils::result<int64_t, utils::error> {
+        if (!id) {
+            return utils::failure(utils::error(sql::error_code::RETRIEVE_DATA_FAILED, "Sequence returned no value"));
+        }
+        return utils::ok(*id);
+    });
+}
+}