# Database Guidelines

> MySQL data and DAO conventions for the library-management system.

---

## Overview

MySQL is the project data layer. DAO classes perform CRUD and query operations
against MySQL. The initial scaffold schema exists at
`src/main/resources/db/schema.sql`; future module tables should follow the same
DDL style and DAO boundaries.

---

## Core Tables

Use primary keys for every table and foreign keys for cross-entity integrity.

Implemented scaffold tables:

- `roles`: administrator, librarian, reader, and future role definitions.
- `permissions`: permission definitions for protected actions.
- `role_permissions`: role-to-permission mapping.
- `users`: login accounts for administrator, librarian, and reader roles.
- `system_logs`: key operation logs, backup events, and exception traces.

Planned module tables:

- `books`: book information, inventory count/status, category reference.
- `book_categories`: category names and descriptions.
- `readers`: reader profiles, borrowing eligibility, contact information.
- `borrow_records`: book-reader borrowing, return, renew, and overdue data.
- `system_logs`: key operation logs, backup events, and exception traces.

Record new schema changes in `src/main/resources/db/schema.sql` and update this
spec with exact table names, key columns, and DAO/service contracts.

---

## DAO Responsibilities

- DAOs own database CRUD and query details.
- Use parameterized SQL or prepared-statement style access; never concatenate
  raw request parameters into SQL.
- Keep transaction boundaries in the service layer for workflows that span
  multiple DAO calls, such as borrow/return operations that also update
  inventory status.
- Return entities or small query result objects to services, not HTML or
  servlet response objects.
- Keep MySQL connection details in `src/main/resources/db.properties` loaded by
  `JdbcUtil`. The required keys are `db.driver`, `db.url`, `db.username`, and
  `db.password`.

---

## Query Guidance

- Book search must support combined lookup by title, author, category, and ID.
- Statistics queries should cover borrowing rankings, inventory reports, and
  overdue reports.
- Borrowing records should preserve enough dates/status fields for borrow,
  return, renew, overdue calculation, and automatic collection status updates.
- Permission queries should support role-based checks for administrator,
  librarian, and reader workflows.

---

## Integrity Constraints

- `books.category_id` should reference `book_categories`.
- `borrow_records.book_id` should reference `books`.
- `borrow_records.reader_id` should reference `readers`.
- Administrator-role and role-permission mapping tables should use foreign keys
  to preserve authorization integrity.
- `users.role_code` must reference `roles.code`.
- `role_permissions.role_code` must reference `roles.code`.
- `role_permissions.permission_code` must reference `permissions.code`.
- Prefer explicit status columns/enums for inventory and borrowing states, then
  document the chosen values once code exists.

## Scenario: Login And Permission Scaffold Schema

### 1. Scope / Trigger

- Trigger: the initial Java Web scaffold introduced a concrete MySQL schema and
  login contract.
- Schema path: `src/main/resources/db/schema.sql`.
- Example configuration path: `src/main/resources/db.properties.example`.

### 2. Signatures

- DAO signature: `UserDao.findActiveByUsername(String username)`.
- Service signature: `AuthService.authenticate(String username, String password)`.
- Permission signature: `AuthService.hasPermission(AuthenticatedUser user, Permission permission)`.
- Servlet route: `POST /login` with `username`, `password`, and optional
  same-application `redirect`.
- Protected routes: `/dashboard`, `/admin/home`, `/librarian/home`, and
  `/reader/home`.
- Session keys: `authenticatedUser`, `userRole`, and `userPermissions`.
- DB config keys: `db.driver`, `db.url`, `db.username`, and `db.password`.
- Login tables: `roles`, `permissions`, `role_permissions`, `users`, and
  `system_logs`.

### 3. Contracts

- `users.username`: unique login identifier submitted by `LoginServlet`.
- `users.password_hash`: PBKDF2 hash in
  `pbkdf2_sha256$iterations$saltBase64$hashBase64` format.
- `users.role_code`: foreign key to `roles.code`; supported scaffold values
  are `administrator`, `librarian`, and `reader`.
- `users.active`: only rows with `active = 1` can authenticate.
- `roles.code`, `permissions.code`, and `role_permissions` must match the Java
  `Role` and `Permission` enum codes exactly.
- `db.properties` must be local configuration. Commit
  `db.properties.example`, but do not commit real credentials.
- Session state stores an `AuthenticatedUser` snapshot, role code, and
  permission-code set. It must not store raw passwords or DAO result objects
  with password hashes.
- Login redirects must stay inside the current application context. Reject
  values that do not start with a single `/` or that contain CR/LF characters.

### 4. Validation & Error Matrix

- Missing username or password -> request returns to login JSP with
  `Username and password are required.`
- Unknown user, inactive user, or hash mismatch -> request returns to login JSP
  with `Invalid username or password.`
- Unsafe or blank redirect -> ignore and route to `/dashboard` after success.
- Missing `db.properties`, JDBC failure, or unsupported role code -> request
  returns a generic service-unavailable message and logs server-side details.
- Authenticated user missing a required permission -> HTTP 403 and
  `WEB-INF/jsp/auth/unauthorized.jsp`.

### 5. Good/Base/Bad Cases

- Good: `admin` resolves to `administrator`, receives all scaffold
  permissions, and can access `/admin/home`.
- Base: `reader` resolves to `reader`, can access `/reader/home`, and cannot
  access `/admin/home`.
- Bad: a JSP reads SQL or password hashes directly from the database. Keep that
  logic in DAO/service code.

### 6. Tests Required

- Compile service/DAO/entity/util classes with `javac` when Maven is
  unavailable.
- Run `PermissionPolicyCheck` or equivalent assertions for administrator,
  librarian, and reader permissions.
- Run `AuthServiceCheck` or equivalent assertions for required-field failures,
  invalid credentials, success, permission checks, and DAO failure fallback.
- When Maven/Tomcat dependencies are installed, run `mvn test` or
  `mvn clean package` to compile Servlet and JSP integration.

### 7. Wrong vs Correct

#### Wrong

```java
// JSP, Servlet, or session code opens JDBC and stores password_hash.
```

#### Correct

```text
login.jsp -> LoginServlet -> AuthService -> UserDao -> users/roles tables
session -> AuthenticatedUser snapshot + role/permission codes only
```