https://github.com/enginooby-practice/hibernate

Configured by XML.
https://github.com/enginooby-practice/hibernate

hibernate hql java jpa mysql xml

Last synced: about 6 hours ago
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Configured by XML.

• Host: GitHub
• URL: https://github.com/enginooby-practice/hibernate
• Owner: enginooby-practice
• Created: 2020-06-29T05:42:02.000Z (over 4 years ago)
• Default Branch: master
• Last Pushed: 2020-07-19T22:08:57.000Z (over 4 years ago)
• Last Synced: 2024-01-10T11:54:01.540Z (10 months ago)
• Topics: hibernate, hql, java, jpa, mysql, xml
• Language: Java
• Homepage:
• Size: 14.3 MB
• Stars: 1
• Watchers: 2
• Forks: 0
• Open Issues: 5
• Metadata Files:
  • Readme: README.md

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README

        
# Practice topics

### Configuration

- Add dependencies: Hibernate and MySQL connector

- Create database 

[[create-db.sql](https://github.com/cpulover-practice/hibernate/blob/master/sql/create-db.sql)]

- Configure Hibernate by XML 

[[hibernate.cfg.xml](https://github.com/cpulover-practice/hibernate/blob/master/src/hibernate.cfg.xml)]

### Concepts

- CRUD features

- SessionFactory, Session and Transaction

- Uni-directional and bi-directional relationship

- Cascade types: CascadeType.ALL, CascadeType.PERSIST (save), CascadeType.REMOVE, CascadeType.DETACH, CascadeType.MERGE, CascadeType.REFRESH

  - 📌 Use persist() with CascadeType.ALL/PERSIST to save all associated objects.

- Eager loading and Lazy loading; Fetch types: Fetch.LAZY (prefer), Fetch.EAGER

  - To retrieve lazy data, a Hibernate session need to be open (connect to the database).

  - 📌 Resolve Lazy loading issue (because of loading after closing session)

    - Option 1: Call getter method while session is still open 

  [[EagerLazyDemo](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/onetomany/EagerLazyDemo.java)]

    - Option 2: Use Hibernate query with HQL [hibernate.query.Query]

  [[FetchJoinDemo](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/onetomany/FetchJoinDemo.java)]

### Entity Class

- Add no-args constructor (required by Hibernate)

- 📌 Add convenience methods for bi-directional one/many-to-many relationship 

[[Instructor](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/entity/Instructor.java)]

- *__@Entity__* [javax.persistence]

- *__@Id__* and *__@GeneratedValue__* (prefer GenerationType.IDENTITY)

- *__@Table:__* map to table in the database [javax.persistence]

- *__@Column:__* map to column of the table

- *__@OneToOne__* 

[[Instructor](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/entity/Instructor.java)

/[InstructorDetail](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/entity/InstructorDetail.java)]

  - Uni-directional (use *__@JoinColumn__*) and bi-directional (add *`mappedBy`* to *__@OneToOne__*)

  -  *__@JoinColum:__* used in the entity class containing the foreign key.

  - *`mappedBy`* attribute: used in the class entity which does not contain the foreign key.

- *__@OneToMany__* 

[[Course](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/entity/Course.java)

/[Review](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/entity/Review.java)]

  - Uni-directional: *__@JoinColumn__* used in the class entity which does not contain the foreign key.

- *__@ManyToMany__* 

[[Student](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/entity/Student.java)

/[Course](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/entity/Course.java)]

  - *`fetch`* should be FetchType.LAZY

  - *`cascade`* should omit CascadeType.REMOVE

  - *__@JoinTable__* with *`joinColumns`* and *`inverseJoinColumns`* for each foreign key

### App Flow

[[CreateDemo](https://github.com/cpulover-practice/hibernate/blob/master/src/com/cpulover/hibernate/onetoone/CreateDemo.java)]

1. Create a Session Factory including all the entities

2. Create a Session

3. Start a Transaction

4. Perfrom CRUD (save/permit if create or update entities)

5. Commit the Transaction

6. Handle connection leak issue: catch error and close Session.

7. Close the Factory