Spring Boot:是否存在@Entity注释? [英] Spring Boot: does @Entity Annotation exist?

问题描述

我看了这个Spring Boot教程: https: //javabrains.io/courses/spring_bootquickstart/lessons/Creating-a-Spring-Data-JPA-Repository

I watched this Spring Boot tutorial: https://javabrains.io/courses/spring_bootquickstart/lessons/Creating-a-Spring-Data-JPA-Repository

，它将@Entity注释放在类名之前.当我尝试在代码中执行此操作时，出现一条错误消息，提示无法解析@Entity".

and it puts an @Entity annotation before a class name. When I tried to do it in my code, I got an Error saying "can't resolve @Entity".

这是我的pom.xml文件:

Here is my pom.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.3.RELEASE</version>
        <relativePath/><!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>


    <dependencies>

        <dependency>
            <groupId>org.eclipse.persistence</groupId>
            <artifactId>javax.persistence</artifactId>
            <version>2.1.0</version>
            <scope>compile</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.apache.derby</groupId>
            <artifactId>derby</artifactId>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

你知道是什么问题吗?

Do you know what is the problem?

推荐答案

我最近也遇到了这个问题.对我来说，spring-boot-starter-data-jpa依赖关系是个问题.尽管它在pom.xml文件中没有任何错误，但是jars不在类路径中-即使在同步maven并以不同方式多次导入依赖项之后(mvn clean/update/install).

I also faced this problem recently. For me, the spring-boot-starter-data-jpa dependency was the issue. Although it was in the pom.xml file without any errors, but the jars were not there in classpath - even after syncing maven and importing dependencies multiple times in different ways ( mvn clean/update/install).

<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

我使用的IDE是IntelliJ Idea.

The IDE I was using was IntelliJ Idea.

最后对我有用的东西:我只是将此依赖关系放在<dependencies> ... </dependencies>标记内的所有其他依赖关系上，即只是更改了依赖关系的顺序并进行了同步.就我而言，这行得通，不知道为什么.

What worked for me at last : I just put this dependency over all other dependencies inside the <dependencies> ... </dependencies> tag, i.e just changed the order of dependencies and synced. That worked in my case, not sure why.

下面是我的pom.xml文件内容供参考.

Below is my pom.xml file contents for reference.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>

<groupId>dev.sanskar.courses</groupId>
<artifactId>course-api</artifactId>
<version>1.0-SNAPSHOT</version>

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.3.RELEASE</version>
</parent>

<dependencies>

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>


    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
    </dependency>


    <!-- https://mvnrepository.com/artifact/javax.persistence/javax.persistence-api -->
    <dependency>
        <groupId>javax.persistence</groupId>
        <artifactId>javax.persistence-api</artifactId>
        <version>2.2</version>
    </dependency>


    <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-validator -->
    <!-- https://mvnrepository.com/artifact/org.hibernate.javax.persistence/hibernate-jpa-2.1-api -->
    <!-- https://mvnrepository.com/artifact/org.hibernate.javax.persistence/hibernate-jpa-2.1-api -->
    <!-- https://mvnrepository.com/artifact/javax.persistence/persistence-api -->


</dependencies>

<properties> 
    <java.version>1.8</java.version>
</properties>


<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>

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