似乎 JPA spring.jpa.hibernate.ddl-auto=update 不起作用

Question

我构建了一个简单的 SpringBoot App（版本：2.4.3）。我有以下实体：

package com.ksteindl.logolo.domain;

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Foo {

    @Id
    private String id;
    private String foo;

    public String getFoo() {
        return foo;
    }

    public void setFoo(String foo) {
        this.foo = foo;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getId() {
        return id;
    }
}

还有一个application.properties

spring.jpa.show-sql=true

spring.datasource.url = jdbc:mysql://localhost:3306/mysql
spring.datasource.username=admin
spring.datasource.password=admin

spring.jpa.database-platform=org.hibernate.dialect.MySQL5Dialect

spring.jpa.hibernate.ddl-auto=update

spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL57Dialect

在第一次运行时，一切似乎都很好。这些表是根据实体创建的。 但是，当我重新启动我的应用程序时，我拥有的每个实体/表都会出现异常。此外，如果我修改我的实体（例如在 Foo 实体中引入 bar 属性），相应的表在数据库中没有改变。 在我看来，它试图重新创建表，但我不知道为什么。 我拥有的每个表/实体都有以下例外：

Hibernate: create table foo (id varchar(255) not null, bar varchar(255), baz varchar(255), foo varchar(255), primary key (id)) engine=InnoDB
2021-04-02 16:34:17.000  WARN 16359 --- [  restartedMain] o.h.t.s.i.ExceptionHandlerLoggedImpl     : GenerationTarget encountered exception accepting command : Error executing DDL "create table foo (id varchar(255) not null, bar varchar(255), baz varchar(255), foo varchar(255), primary key (id)) engine=InnoDB" via JDBC Statement

org.hibernate.tool.schema.spi.CommandAcceptanceException: Error executing DDL "create table foo (id varchar(255) not null, bar varchar(255), baz varchar(255), foo varchar(255), primary key (id)) engine=InnoDB" via JDBC Statement
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:67) ~[hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.applySqlString(AbstractSchemaMigrator.java:559) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.applySqlStrings(AbstractSchemaMigrator.java:504) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.createTable(AbstractSchemaMigrator.java:277) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.tool.schema.internal.GroupedSchemaMigratorImpl.performTablesMigration(GroupedSchemaMigratorImpl.java:71) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.performMigration(AbstractSchemaMigrator.java:207) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.tool.schema.internal.AbstractSchemaMigrator.doMigration(AbstractSchemaMigrator.java:114) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.performDatabaseAction(SchemaManagementToolCoordinator.java:184) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.tool.schema.spi.SchemaManagementToolCoordinator.process(SchemaManagementToolCoordinator.java:73) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:318) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:468) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:1259) [hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:58) [spring-orm-5.3.4.jar:5.3.4]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) [spring-orm-5.3.4.jar:5.3.4]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:409) [spring-orm-5.3.4.jar:5.3.4]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:396) [spring-orm-5.3.4.jar:5.3.4]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) [spring-orm-5.3.4.jar:5.3.4]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1845) [spring-beans-5.3.4.jar:5.3.4]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1782) [spring-beans-5.3.4.jar:5.3.4]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:602) [spring-beans-5.3.4.jar:5.3.4]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:524) [spring-beans-5.3.4.jar:5.3.4]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) [spring-beans-5.3.4.jar:5.3.4]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.4.jar:5.3.4]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) [spring-beans-5.3.4.jar:5.3.4]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) [spring-beans-5.3.4.jar:5.3.4]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1153) ~[spring-context-5.3.4.jar:5.3.4]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:907) ~[spring-context-5.3.4.jar:5.3.4]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:582) ~[spring-context-5.3.4.jar:5.3.4]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:144) ~[spring-boot-2.4.3.jar:2.4.3]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:767) ~[spring-boot-2.4.3.jar:2.4.3]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) ~[spring-boot-2.4.3.jar:2.4.3]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:426) ~[spring-boot-2.4.3.jar:2.4.3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:326) ~[spring-boot-2.4.3.jar:2.4.3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1311) ~[spring-boot-2.4.3.jar:2.4.3]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1300) ~[spring-boot-2.4.3.jar:2.4.3]
    at com.ksteindl.logolo.LogoloApplication.main(LogoloApplication.java:10) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_282]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_282]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_282]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_282]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) ~[spring-boot-devtools-2.4.3.jar:2.4.3]
Caused by: java.sql.SQLSyntaxErrorException: Table 'foo' already exists
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:120) ~[mysql-connector-java-8.0.23.jar:8.0.23]
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) ~[mysql-connector-java-8.0.23.jar:8.0.23]
    at com.mysql.cj.jdbc.StatementImpl.executeInternal(StatementImpl.java:762) ~[mysql-connector-java-8.0.23.jar:8.0.23]
    at com.mysql.cj.jdbc.StatementImpl.execute(StatementImpl.java:646) ~[mysql-connector-java-8.0.23.jar:8.0.23]
    at com.zaxxer.hikari.pool.ProxyStatement.execute(ProxyStatement.java:95) ~[HikariCP-3.4.5.jar:na]
    at com.zaxxer.hikari.pool.HikariProxyStatement.execute(HikariProxyStatement.java) ~[HikariCP-3.4.5.jar:na]
    at org.hibernate.tool.schema.internal.exec.GenerationTargetToDatabase.accept(GenerationTargetToDatabase.java:54) ~[hibernate-core-5.4.28.Final.jar:5.4.28.Final]
    ... 40 common frames omitted

有人可以帮帮我吗？谢谢

Answer 1

在某些情况下，Hibernate 无法自行对数据库架构进行一些更改。

这就是为什么我们通常尽量不将ddl-auto 设置为update，我们更喜欢使用像liquibase 或flyway 这样的数据迁移工具。

在非常简单的情况下，例如添加一列，Hibernate 会很好地工作，因为它是一个非破坏性更改。另一方面，如果你想删除一列，它会变得更加微妙。在这种情况下，您的 java 实体将不再知道该列，但在数据库中它仍然存在。

这既是一个问题，也是一件好事，因为 Hibernate 确保您不会丢失数据，但这也是没有进行某些更改的原因。

正如我在上面告诉你的，我们更喜欢使用数据迁移工具，这些工具就是为做这类事情而设计的。

例如，您可以看看 Liquibase，这是一个非常好的工具。 以下是一些有用的链接：

• https://www.liquibase.org/
• https://docs.liquibase.com/tools-integrations/springboot/springboot.html
• https://www.baeldung.com/liquibase-refactor-schema-of-java-app

但你也可以使用flyway（我不知道）：https://flywaydb.org/

最后，这里有一个比较有趣的 Liquibase 和 Flyway 的比较：https://dzone.com/articles/flyway-vs-liquibase

Answer 2

看起来在 2.4.3 SpringBoot JPA ddl-auto=update 行为不适用于 MySql 8。 在 PostgreSQL 13 中，ddl-auto=update 行为完美运行，没有任何错误。 我的application.yml

spring:
  jpa:
    hibernate:
      ddl-auto: update
    database-platform: org.hibernate.dialect.PostgreSQLDialect
  datasource:
    url: "jdbc:postgresql://localhost:5432/mydb"
    username: myuser
    password: mypassword

如果有人可以确认/反驳，那将是令人放心的。