https://github.com/nfriaa/hibernate-tutorial4
Hibernate tutorial 3 : Hibernate "Many to One" association
https://github.com/nfriaa/hibernate-tutorial4
annotations hibernate hibernate5 java many-to-one maven mysql
Last synced: 7 months ago
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Hibernate tutorial 3 : Hibernate "Many to One" association
- Host: GitHub
- URL: https://github.com/nfriaa/hibernate-tutorial4
- Owner: nfriaa
- License: mit
- Created: 2017-10-09T15:43:01.000Z (almost 8 years ago)
- Default Branch: master
- Last Pushed: 2017-10-18T17:41:18.000Z (almost 8 years ago)
- Last Synced: 2025-01-16T07:55:46.662Z (9 months ago)
- Topics: annotations, hibernate, hibernate5, java, many-to-one, maven, mysql
- Language: Java
- Size: 15.6 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# hibernate-tutorial4
Hibernate tutorial 4 : **"Many To One"** association
[](https://github.com/nfriaa/hibernate-tutorial4/issues) [](https://github.com/nfriaa/hibernate-tutorial4) [](https://github.com/nfriaa/hibernate-tutorial4/blob/master/LICENSE)
## Description
A sample code to learn how to map **"Many To One"** relationship between two entities using the Hibernate ORM.
* JavaSE 8
* Hibernate 5 / Annotations
* Hibernate **"Many To One"** association
* Maven 4
* MySQL 5
## 1. Database
Create only database, don't create tables (tables will be created by Hibernate)
* database name : **persist_db**
```sql
CREATE DATABASE `persist_db` /*!40100 DEFAULT CHARACTER SET utf8 */
```
## 2. Maven "pom.xml" dependencies
```xml
mysql
mysql-connector-java
6.0.6
org.hibernate
hibernate-core
5.2.11.Final
```
## 3. Hibernate configuration file "hibernate.cfg.xml"
```xml
org.hibernate.dialect.MySQL5InnoDBDialect
jdbc:mysql://localhost:3306/persist_db?useTimezone=true&serverTimezone=UTC
root
true
false
create
```
* hibernate.hbm2ddl.auto : "create" => creates the schema necessary for defined entities, destroying any previous data
* don't forget to map the two entities in this XML config file (Product and Category)
## 4. "Many To One" association
`Source entity : Product.java`
```java
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.ForeignKey;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
@Entity
@Table(name = "product")
public class Product
{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", nullable = false)
private int id;
@Column(name = "name", length = 255, nullable = true)
private String name;
@Column(name = "price", nullable = true)
private int price;
@ManyToOne
@JoinColumn(name = "category_id", foreignKey = @ForeignKey(name = "CATEGORY_ID_FK"))
private Category category;
// Getters and Setters here...
}
```
- @ManyToOne : is equivalent to foreign key relationship in a database
- @JoinColumn : name of the foreign key column in the *source entity*
- @ForeignKey : name of the constraint (foreign key) in the *destination entity*
`Destination entity : Category.java`
```java
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name = "category")
public class Category
{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", nullable = false)
private int id;
@Column(name = "name", length = 255, nullable = true)
private String name;
// Getters and Setters here...
}
```
## 5. Main Class "Application.java"
* create main class to test the code
* example :
```java
// new category
Category category_a = new Category();
category_a.setName("Cat a");
session.save(category_a);
// new product
Product product_x = new Product();
product_x.setName("Prod x");
product_x.setPrice(456);
product_x.setCategory(category_a);
session.save(product_x);
```