feat(database): Add query to fetch all grades

src/g2_2025_grade_calculator_pkg/src/database/DatabaseManager.cpp

@@ -207,4 +207,32 @@ void DatabaseManager::insert_sample_data() {
     }
 }
 
+int DatabaseManager::get_final_course_grade(const StudentCourse& sc) {
+    if (!is_connected()) return -1;
+
+    try {
+        pqxx::work txn(*conn_);
+
+        auto result = txn.exec_params(SQL_SELECT_STUDENT_COURSE_RESULTS, sc.student_name, sc.course_name);
+
+        if (result.size() == 1) {
+            int exam_count = result[0][0].as<int>();
+            if (exam_count == 0) {
+                return -1; // No exams taken
+            }
+            int avg_grade = static_cast<int>(result[0][1].as<double>() + 0.5);
+            return avg_grade;
+        } else {
+            return -1; // No results found
+        }
+
+    } catch (const pqxx::sql_error &e) {
+        RCLCPP_ERROR(logger_, "[DBS] get final course grade failed: %s", e.what());
+        return -1;
+    } catch (const std::exception &e) {
+        RCLCPP_ERROR(logger_, "[DBS] database error: %s", e.what());
+        return -1;
+    }
+}
+
 } // namespace assignments::one::exam_result_generator

src/g2_2025_grade_calculator_pkg/src/database/DatabaseManager.hpp

@@ -36,6 +36,9 @@ public:
     bool store_exam_result(const std::string& student_name, const std::string& course_name, int grade);
     bool enroll_student_into_course(const StudentCourse& sc);
     bool store_final_course_result(const StudentCourse& sc, int exam_count, int final_grade);
+
+    int get_final_course_grade(const StudentCourse& sc);
+
 private:
     rclcpp::Logger logger_;
 

src/g2_2025_grade_calculator_pkg/src/database/SQLQueries.hpp

@@ -51,6 +51,12 @@ static const std::string SQL_SELECT_MISSING_RESULTS = R"(
     WHERE fcr.id IS NULL
 )";
 
+static const std::string SQL_SELECT_STUDENT_COURSE_RESULTS = R"(
+    SELECT COUNT(*), AVG(exam_grade)
+    FROM exam_results
+    WHERE student_name = $1 AND course_name = $2
+)";
+
 static const std::string SQL_INSERT_EXAM_RESULT = R"(
     INSERT INTO exam_results (student_name, course_name, exam_grade)
     VALUES ($1, $2, $3)