problem

Springboot 2.0 project, start error, exception: nested exception is java.lang.IllegalArgumentException : At least one JPA metamodel must be present!。

Details are as follows:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jpaMappingContext': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: At least one JPA metamodel must be present!
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1710) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:583) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:502) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:312) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:228) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:310) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:741) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:868) ~[spring-context-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:752) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:388) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1246) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1234) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
	at com.example.demo.JtademoApplication.main(JtademoApplication.java:22) [classes/:na]
Caused by: java.lang.IllegalArgumentException: At least one JPA metamodel must be present!
	at org.springframework.util.Assert.notEmpty(Assert.java:450) ~[spring-core-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.data.jpa.mapping.JpaMetamodelMappingContext.<init>(JpaMetamodelMappingContext.java:54) ~[spring-data-jpa-2.0.5.RELEASE.jar:2.0.5.RELEASE]
	at org.springframework.data.jpa.repository.config.JpaMetamodelMappingContextFactoryBean.createInstance(JpaMetamodelMappingContextFactoryBean.java:88) ~[spring-data-jpa-2.0.5.RELEASE.jar:2.0.5.RELEASE]
	at org.springframework.data.jpa.repository.config.JpaMetamodelMappingContextFactoryBean.createInstance(JpaMetamodelMappingContextFactoryBean.java:43) ~[spring-data-jpa-2.0.5.RELEASE.jar:2.0.5.RELEASE]
	at org.springframework.beans.factory.config.AbstractFactoryBean.afterPropertiesSet(AbstractFactoryBean.java:141) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1769) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1706) ~[spring-beans-5.0.4.RELEASE.jar:5.0.4.RELEASE]
	... 16 common frames omitted

analysis

Spring boot supports JPA through spring boot starter data JPA. The default JPA implementer of spring boot is hibernate.
Due to pom.xml Spring boot starter data JPA is defined in the file.
<dependency>
            <groupId> org.springframework.boot&lt ;/groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>    

At this time, the project will automatically open the following two auto configuration classes:
jparepositoriesautoconfiguration
hibernatejpaautoconfiguration

As long as there is such a definition, the JPA metamodelmappingcontext class will check during the startup process. At least one JPA metamodel must be defined. Otherwise, an at least one JPA metamodel must be present! Error will be reported.

The relevant source code of jpametametamodelmappingcontext is as follows:

/**
	 * Creates a new JPA {@link Metamodel} based {@link MappingContext}.
	 *
	 * @param models must not be {@literal null} or empty.
	 */
	public JpaMetamodelMappingContext(Set<Metamodel> models) {

		Assert.notNull(models, "JPA metamodel must not be null!");
		Assert.notEmpty(models, "At least one JPA metamodel must be present!");

		this.models = models;
		this.persistenceProvider = PersistenceProvider.fromMetamodel(models.iterator().next());
	}

solve

Method 1: if JPA is not used in the system, remove the spring boot starter data JPA dependency.

Method 2: add @ enableautoconfiguration (exclude = {jparepositor) to the application iesAutoConfiguration.class }) notes.

Method 2 is mainly used for custom JPA configuration implementation.

The end of the article.