在 Intellij Idea 中使用 hibernate 从实体类生成数据库表（不使用 Spring）

Question

请问，有什么方法可以在 Intellij Idea 中使用 hibernate 从实体类生成数据库表？我在网上看到的只是从数据库模式生成实体类。但是当我修改任何实体类时，我需要相反的方式来轻松更新我的数据库。

这是我的 hibernate.cfg.xml 文件

<property name="connection.driver_class">com.mysql.cj.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost:3306/my_db?useSSL=false</property>


<property name="connection.username">username</property>
<property name="connection.password">password</property>


<property name="dialect">org.hibernate.dialect.MySQL8Dialect</property>

<property name="show_sql">true</property>

<property name="current_session_context_class">thread</property>

<property name="hbm2ddl.auto">create</property>


<property name="connection.pool_size">1</property>
<property name="hibernate.dbcp.initialSize">5</property>
<property name="hibernate.dbcp.maxTotal">20</property>
<property name="hibernate.dbcp.maxIdle">10</property>
<property name="hibernate.dbcp.minIdle">5</property>
<property name="hibernate.dbcp.maxWaitMillis">-1</property>


<!--Declaring entity classes to be mapped to the database-->
<mapping class="com.softpager.estores.entities.Order" />
<mapping class="com.softpager.estores.entities.Customer" />
<mapping class="com.softpager.estores.entities.Users" />
<mapping class="com.softpager.estores.entities.Product" />   

这是我的 persistence.xml 文件

 <persistence-unit name="EStores">
    <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
    <properties>
        <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/my_db?useSSL=false"/>
        <property name="hibernate.connection.driver_class" value="com.mysql.cj.jdbc.Driver"/>
        <property name="hibernate.connection.username" value="username"/>
        <property name="hibernate.connection.password" value="password"/>
        <property name="hibernate.archive.autodetection" value="class"/>
        <property name="hibernate.show_sql" value="true"/>
        <property name="hibernate.format_sql" value="true"/>
        <property name="hibernate.hbm2ddl.auto" value="create"/>

        <property name="javax.persistence.schema-generation.database.action" value="drop-and-create"/>
        <property name="javax.persistence.schema-generation.create-source" value="metadata"/>
        <property name="javax.persistence.schema-generation.drop-source" value="metadata"/>
        <property name="javax.persistence.sql-load-script-source" value="META-INF/load.sql"/>
    </properties>

</persistence-unit>

这是我的 Main.class

public class Main {
public static void main(String[] args) {
    EntityManagerFactory factory = createEntityManagerFactory("EStores");
    EntityManager entityManager = factory.createEntityManager();

}

}

示例实体类

@Data
@Entity
@Table(name = "customer")
public class Customer {

@Id
@GeneratedValue
@Column(name = "customer_id")
private long id;

@Column(name = "first_name", nullable = false)
private String firstName;

@Column(name = "last_name", nullable = false)
private String lastName;

@Embedded
private Contact contact;

@Embedded
private Address address;

@OneToMany(fetch = FetchType.LAZY, mappedBy = "customer")
private Set<Review> reviews;

@OneToMany(fetch = FetchType.LAZY, mappedBy = "customer")
private Set<Product> products;


 public Customer(String firstName, String lastName, Contact contact,              
                                                  Address address) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.contact = contact;
    this.address = address;
    this.products = new HashSet<>();
    this.reviews = new HashSet<>();
}

}

Answer 1

我建议against using hbm2ddl.auto，您可以将Liquibase 添加到您的项目中。它允许您使用更改日志管理所有数据库架构修改，并且您可以独立于应用启动运行表生成/更新。

这确实在您修改模型和正在更新的数据库之间增加了一个额外的步骤，因为您必须将所有更改添加到更改日志中。我建议使用 JPA Buddy 插件，它可以通过将您的 Java 模型与当前数据库进行比较来生成更改日志， here is how it looks

Answer 2

如果我说得对，您想从 Java 类生成数据库表，对吗？如果是这样，这就是 ORM 的主要概念。每当您创建一个新的 POJO 并使用 @Entity 对其进行注释时，您就是在告诉 hibernate 使用该类中的数据创建一个表（如果不存在的话）。在下面找到一个可以做到这一点的示例：

package com.test.simple_crud_application.models;

import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.UpdateTimestamp;

import javax.persistence.*;
import java.io.Serializable;
import java.time.LocalDateTime;

@Entity
@Table(name = "users")
public class User implements Serializable
{
    @CreationTimestamp
    @Column(name = "created_at", updatable = false, nullable = false)
    private LocalDateTime createdAt;
    @UpdateTimestamp
    @Column(name = "updated_at", updatable = true, nullable = false)
    private LocalDateTime modifiedAt;

    @Id
    @GeneratedValue(generator="system-uuid")
    @GenericGenerator(name="system-uuid", strategy = "uuid")
    @Column(name = "uid", unique = true, nullable = false)
    private String uid;

    @Column(name = "username", nullable = false)
    private String username;

    @Column(name = "password", nullable = false)
    private String password;
}

Answer 3

使用 JPA Buddy 一个 IntelliJ IDEA 插件，它是免费的。

在 JPA 结构 视图中右键单击您的实体，然后单击显示 DDL。