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docs: update metadata mapping

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Ilkka Seppälä
2024-05-26 14:46:07 +03:00
parent 6d961b54d7
commit d03b2362db
1 changed files with 75 additions and 16 deletions
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metadata-mapping/README.md
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@@ -15,9 +15,9 @@ Metadata Mapping is designed to manage the mapping between database records and
## Explanation
Real world example
Real-world example
> Hibernate ORM Tool uses Metadata Mapping Pattern to specify the mapping between classes and tables either using XML or annotations in code.
> An analogous real-world example of the Metadata Mapping design pattern can be seen in online retail systems. In such systems, products often have varying attributes depending on their category. For instance, electronics might have attributes like battery life and screen size, while clothing might have attributes like size and fabric type. Using Metadata Mapping, the system can dynamically map these varying attributes to the product objects without modifying the underlying class structure. This flexibility allows for easy updates and management of product attributes as new categories and attributes are introduced, ensuring that the system can evolve with the changing product landscape.
In plain words
@@ -29,6 +29,8 @@ Wikipedia says
**Programmatic Example**
Hibernate ORM Tool uses Metadata Mapping Pattern to specify the mapping between classes and tables either using XML or annotations in code.
We give an example about visiting the information of `user_account` table in `h2` database. Firstly, we create `user_account` table with `h2`:
```java
@@ -43,9 +45,6 @@ public class DatabaseUtil {
+ " PRIMARY KEY (`id`)\n"
+ ");";
/**
* Create database.
*/
static {
LOGGER.info("create h2 database");
var source = new JdbcDataSource();
@@ -70,11 +69,6 @@ public class User {
private String username;
private String password;
/**
* Get a user.
* @param username user name
* @param password user password
*/
public User(String username, String password) {
this.username = username;
this.password = password;
@@ -133,10 +127,6 @@ Then we can get access to the table just like an object with `Hibernate`, here's
public class UserService {
private static final SessionFactory factory = HibernateUtil.getSessionFactory();
/**
* List all users.
* @return list of users
*/
public List<User> listUser() {
LOGGER.info("list all users.");
List<User> users = new ArrayList<>();
@@ -162,9 +152,78 @@ public class UserService {
}
```
## Class diagram
Here is our `App` class with `main` function for running the example.
![Metadata Mapping](./etc/metamapping.png)
```java
@Slf4j
public class App {
public static void main(String[] args) {
// get service
var userService = new UserService();
// use create service to add users
for (var user : generateSampleUsers()) {
var id = userService.createUser(user);
LOGGER.info("Add user" + user + "at" + id + ".");
}
// use list service to get users
var users = userService.listUser();
LOGGER.info(String.valueOf(users));
// use get service to get a user
var user = userService.getUser(1);
LOGGER.info(String.valueOf(user));
// change password of user 1
user.setPassword("new123");
// use update service to update user 1
userService.updateUser(1, user);
// use delete service to delete user 2
userService.deleteUser(2);
// close service
userService.close();
}
public static List<User> generateSampleUsers() {
final var user1 = new User("ZhangSan", "zhs123");
final var user2 = new User("LiSi", "ls123");
final var user3 = new User("WangWu", "ww123");
return List.of(user1, user2, user3);
}
}
```
Console output:
```
14:44:17.792 [main] INFO org.hibernate.Version - HHH000412: Hibernate ORM core version 5.6.12.Final
14:44:17.977 [main] INFO o.h.annotations.common.Version - HCANN000001: Hibernate Commons Annotations {5.1.2.Final}
14:44:18.216 [main] WARN o.hibernate.orm.connections.pooling - HHH10001002: Using Hibernate built-in connection pool (not for production use!)
14:44:18.217 [main] INFO o.hibernate.orm.connections.pooling - HHH10001005: using driver [org.h2.Driver] at URL [jdbc:h2:mem:metamapping]
14:44:18.217 [main] INFO o.hibernate.orm.connections.pooling - HHH10001001: Connection properties: {}
14:44:18.217 [main] INFO o.hibernate.orm.connections.pooling - HHH10001003: Autocommit mode: false
14:44:18.219 [main] INFO o.h.e.j.c.i.DriverManagerConnectionProviderImpl - HHH000115: Hibernate connection pool size: 1 (min=1)
14:44:18.276 [main] INFO org.hibernate.dialect.Dialect - HHH000400: Using dialect: org.hibernate.dialect.H2Dialect
14:44:18.463 [main] INFO o.hibernate.orm.connections.access - HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@73a8e994] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
14:44:18.465 [main] INFO o.hibernate.orm.connections.access - HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@7affc159] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
14:44:18.470 [main] INFO o.h.e.t.j.p.i.JtaPlatformInitiator - HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
14:44:18.473 [main] INFO c.i.metamapping.service.UserService - create user: ZhangSan
14:44:18.508 [main] INFO c.i.metamapping.service.UserService - create user ZhangSan at 1
14:44:18.508 [main] INFO com.iluwatar.metamapping.App - Add userUser(id=1, username=ZhangSan, password=zhs123)at1.
14:44:18.508 [main] INFO c.i.metamapping.service.UserService - create user: LiSi
14:44:18.509 [main] INFO c.i.metamapping.service.UserService - create user LiSi at 2
14:44:18.509 [main] INFO com.iluwatar.metamapping.App - Add userUser(id=2, username=LiSi, password=ls123)at2.
14:44:18.509 [main] INFO c.i.metamapping.service.UserService - create user: WangWu
14:44:18.512 [main] INFO c.i.metamapping.service.UserService - create user WangWu at 3
14:44:18.512 [main] INFO com.iluwatar.metamapping.App - Add userUser(id=3, username=WangWu, password=ww123)at3.
14:44:18.512 [main] INFO c.i.metamapping.service.UserService - list all users.
14:44:18.542 [main] INFO com.iluwatar.metamapping.App - [User(id=1, username=ZhangSan, password=zhs123), User(id=2, username=LiSi, password=ls123), User(id=3, username=WangWu, password=ww123)]
14:44:18.542 [main] INFO c.i.metamapping.service.UserService - get user at: 1
14:44:18.545 [main] INFO com.iluwatar.metamapping.App - User(id=1, username=ZhangSan, password=zhs123)
14:44:18.545 [main] INFO c.i.metamapping.service.UserService - update user at 1
14:44:18.548 [main] INFO c.i.metamapping.service.UserService - delete user at: 2
14:44:18.550 [main] INFO o.h.t.s.i.SchemaDropperImpl$DelayedDropActionImpl - HHH000477: Starting delayed evictData of schema as part of SessionFactory shut-down'
14:44:18.550 [main] INFO o.hibernate.orm.connections.access - HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@7b5cc918] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
14:44:18.551 [main] INFO o.hibernate.orm.connections.pooling - HHH10001008: Cleaning up connection pool [jdbc:h2:mem:metamapping]
```
## Applicability