java 从实体创建数据库表
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Create database tables from entities
提问by Matt Mcdon
Is in hibernate something like code first approach from Entity Framework? I am trying to prepare database tables from java classes (MySQL). I have already prepared java classes with JPA annotations, but I am not sure what to do now (I am using IntelliJ). What should I have in my main to create thoose tables? Or should I use some tools?
在休眠中是否类似于实体框架中的代码优先方法？我正在尝试从 Java 类 (MySQL) 准备数据库表。我已经准备好了带有 JPA 注释的 java 类，但我不确定现在该怎么做（我正在使用 IntelliJ）。我的主要内容应该有什么来创建那些表？还是我应该使用一些工具？
One of my classes looks like this:
我的一堂课看起来像这样：
@Entity
public class Item {
@Id
@GeneratedValue
private long id;
@Column
private String text;
@ManyToMany(mappedBy = "items")
private Set<Container> containers = new HashSet<Container>();
public long getId() {
return id;
}
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
public Set<Container> getContainers() { return containers; }
}
采纳答案by Matt Mcdon
For clarification: I was using JPA2, so configuration was in persistence.xml. What worked for me was setting:
澄清一下：我使用的是 JPA2，所以配置在persistence.xml 中。对我有用的是设置：
<property name="hibernate.hbm2ddl.auto">create</property>
without "hibernate."it was not working.
没有“休眠”。它不起作用。
Also to start it I needed to prepare main function with creating EntityManager, because mapping to db happens when it is created:
同样要启动它，我需要通过创建 EntityManager 来准备主函数，因为在创建时会映射到 db：
public static void main(String [] args){
EntityManagerFactory factory = Persistence.createEntityManagerFactory("NewPersistenceUnit"); //name of persistence unit here
EntityManager entityManager = factory.createEntityManager();
}
回答by siva636
You need to set the hibernate.hbm2ddl.autoproperty with value create. If so, when you run the applications first time, the tables will be created.
您需要hibernate.hbm2ddl.auto使用 value设置属性create。如果是这样，当您第一次运行应用程序时，将创建表。
回答by Chaitanya
In hibernate.cfg.xml configuration file you can set a property called hbm2ddl.autothat tells hibernate to create a table for you:
在 hibernate.cfg.xml 配置文件中，您可以设置一个名为的属性hbm2ddl.auto，它告诉 hibernate 为您创建一个表：
<property name="hbm2ddl.auto">create</property>
When you run your application for the first time then you can set the property to createand later you can change it to update.
当您第一次运行应用程序时，您可以将该属性设置为create，稍后您可以将其更改为update。
Follow this link for more details:
请点击此链接了解更多详情：
回答by Thamil
@OneToMany(mappedBy = "")
@Fetch(value = FetchMode.SUBSELECT)
@OneToMany(mappedBy = "")
@Fetch(value = FetchMode.SUBSELECT)
In my case, I have mentioned the same OneToManyrelationship two times in a master table. Because I have two relationships. I have used @Fetch(value = FetchMode.SUBSELECT)in two relationships. This is working for me fine.
就我而言，我OneToMany在主表中两次提到了相同的关系。因为我有两种关系。我@Fetch(value = FetchMode.SUBSELECT)在两个关系中使用过。这对我来说很好。
