project-init

db.py

@@ -0,0 +1,135 @@
+"""
+Database layer: connect to MySQL, verify/create the student_db database,
+and verify/create the STUDENT, GUARDIAN and ATTENDANCE tables per the
+schema (Tables 9.3, 9.4, 9.5).
+
+Schema notes:
+- GUARDIAN.GUID is the primary key (12-digit Aadhaar number, stored as CHAR(12)).
+- STUDENT.GUID is a foreign key referencing GUARDIAN.GUID.
+- ATTENDANCE has a composite primary key (AttendanceDate, RollNumber), and
+  RollNumber is also a foreign key referencing STUDENT.RollNumber.
+- Because STUDENT references GUARDIAN, GUARDIAN must be created first.
+"""
+
+import sys
+
+import pymysql
+import pymysql.cursors
+
+import config
+
+# Table creation statements, in dependency order (GUARDIAN -> STUDENT -> ATTENDANCE)
+TABLE_DEFINITIONS = {
+	"GUARDIAN": """
+		CREATE TABLE GUARDIAN (
+			GUID    CHAR(12)    NOT NULL,
+			GName   VARCHAR(20) NOT NULL,
+			GPhone  CHAR(10)    NULL,
+			GAddress VARCHAR(30) NOT NULL,
+			PRIMARY KEY (GUID),
+			UNIQUE (GPhone)
+		) ENGINE=InnoDB
+	""",
+	"STUDENT": """
+		CREATE TABLE STUDENT (
+			RollNumber   INT         NOT NULL,
+			SName        VARCHAR(20) NOT NULL,
+			SDateofBirth DATE        NOT NULL,
+			GUID         CHAR(12)    NOT NULL,
+			PRIMARY KEY (RollNumber),
+			FOREIGN KEY (GUID) REFERENCES GUARDIAN(GUID)
+				ON DELETE RESTRICT ON UPDATE CASCADE
+		) ENGINE=InnoDB
+	""",
+	"ATTENDANCE": """
+		CREATE TABLE ATTENDANCE (
+			AttendanceDate   DATE     NOT NULL,
+			RollNumber       INT      NOT NULL,
+			AttendanceStatus CHAR(1)  NOT NULL,
+			PRIMARY KEY (AttendanceDate, RollNumber),
+			FOREIGN KEY (RollNumber) REFERENCES STUDENT(RollNumber)
+				ON DELETE CASCADE ON UPDATE CASCADE,
+			CONSTRAINT chk_attendance_status CHECK (AttendanceStatus IN ('P', 'A'))
+		) ENGINE=InnoDB
+	""",
+}
+
+# Creation order matters because of foreign keys.
+TABLE_ORDER = ["GUARDIAN", "STUDENT", "ATTENDANCE"]
+
+
+def connect_server(database=None):
+	"""Connect to the MySQL server (optionally selecting a database)."""
+	try:
+		conn = pymysql.connect(
+			host=config.DB_HOST,
+			port=config.DB_PORT,
+			user=config.DB_USER,
+			password=config.DB_PASSWORD,
+			database=database,
+			connect_timeout=config.DB_CONNECT_TIMEOUT,
+			cursorclass=pymysql.cursors.DictCursor,
+			autocommit=False,
+		)
+		return conn
+	except pymysql.err.OperationalError as e:
+		print(f"\n[ERROR] Could not connect to MySQL server at "
+			  f"{config.DB_HOST}:{config.DB_PORT} as user '{config.DB_USER}'.")
+		print(f"        Details: {e}")
+		sys.exit(1)
+
+
+def ensure_database():
+	"""Verify the student_db database exists; create it if it does not."""
+	conn = connect_server(database=None)
+	try:
+		with conn.cursor() as cur:
+			cur.execute("SHOW DATABASES LIKE %s", (config.DB_NAME,))
+			exists = cur.fetchone() is not None
+			if exists:
+				print(f"[OK] Database '{config.DB_NAME}' found.")
+			else:
+				print(f"[..] Database '{config.DB_NAME}' not found. Creating it...")
+				cur.execute(
+					f"CREATE DATABASE `{config.DB_NAME}` "
+					"CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci"
+				)
+				conn.commit()
+				print(f"[OK] Database '{config.DB_NAME}' created.")
+	finally:
+		conn.close()
+
+
+def ensure_tables(conn):
+	"""Verify each required table exists; create any that are missing."""
+	with conn.cursor() as cur:
+		cur.execute("SHOW TABLES")
+		existing = {row[f"Tables_in_{config.DB_NAME}"] for row in cur.fetchall()}
+
+	for table in TABLE_ORDER:
+		if table in existing:
+			print(f"[OK] Table '{table}' found.")
+		else:
+			print(f"[..] Table '{table}' not found. Creating it...")
+			with conn.cursor() as cur:
+				cur.execute(TABLE_DEFINITIONS[table])
+			conn.commit()
+			print(f"[OK] Table '{table}' created.")
+
+
+def get_connection():
+	"""
+	Full startup sequence:
+	1. Ensure the student_db database exists (creating it if needed).
+	2. Connect to student_db.
+	3. Ensure all required tables exist (creating any that are missing).
+	Returns an open connection to student_db, ready for use.
+	"""
+	print(f"Connecting to MySQL server at {config.DB_HOST}:{config.DB_PORT} ...")
+	ensure_database()
+
+	conn = connect_server(database=config.DB_NAME)
+	print(f"[OK] Connected to database '{config.DB_NAME}'.")
+
+	ensure_tables(conn)
+	return conn