如何在 Spring Boot 中使用 JPA 中的 Criteria？

Question

我正在使用 JPA 和弹簧靴。 我是 JPA 的新手。 我想通过传递函数的值来检索一个对象。 但在示例中，它是通过休眠配置完成的。 我的类路径中没有配置sessionFactory bean 。 我想使用 JPA 来检索对象。 在示例中，它是：

// Transactional for Hibernate
@Transactional
public class AccountDAOImpl implements AccountDAO {

  @Autowired
private EntityManager entityManager;
    
    @Override
    public Account findAccount(String userName) {
        Session session = sessionFactory.getCurrentSession();
        Criteria crit = session.createCriteria(Account.class);
        crit.add(Restrictions.eq("userName", userName));
        return (Account) crit.uniqueResult();
    }
}

但我在 JPA 中尝试过这样的：

// Transactional for Hibernate
@Transactional
public class AccountDAOImpl implements AccountDAO {

    @Autowired
    private EntityManager em;

    @Override
    public Account findAccount(String userName) {
      CriteriaBuilder cm= em.getCriteriaBuilder();
      cm.createQuery(Account.class);
        cm.add(Restrictions.eq("userName", userName));
        return (Account) crit.uniqueResult();
    }
}

但它向我显示错误，如何使用 JPA 传递用户名？

我的 pom.xml 是：

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.ashwin</groupId>
    <artifactId>vemployee</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>vemployee</name>
    <description>Demo project for Spring Boot for offc</description>

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

    <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>

        <!-- Spring Security Core -->
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-core</artifactId>
        </dependency>

        <!-- Spring Security Config -->
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-config</artifactId>
        </dependency>

        <!-- Spring Security Web -->
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>

        <!-- https://mvnrepository.com/artifact/jstl/jstl -->
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>

        <!-- needed for jsp -->
        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-jasper</artifactId>
            <version>9.0.27</version>
        </dependency>

        <!--bootsrap and jquery-->
        <dependency>
            <groupId>org.webjars</groupId>
            <artifactId>bootstrap</artifactId>
            <version>4.3.1</version>
        </dependency>
        <dependency>
            <groupId>org.webjars</groupId>
            <artifactId>jquery</artifactId>
            <version>3.4.0</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.webjars/bootstrap-datepicker -->
        <dependency>
            <groupId>org.webjars</groupId>
            <artifactId>bootstrap-datepicker</artifactId>
            <version>1.7.1</version>
        </dependency>

        <dependency>
            <groupId>commons-fileupload</groupId>
            <artifactId>commons-fileupload</artifactId>
            <version>1.4</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

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

</project>

我也试过如下：

    TypedQuery<Account> query=em.createQuery("Select a from Account a where a.userName = :userName",Account.class);
      query.setParameter(1,userName);
    Account acc=query.getResultList().get(0);
    return acc;

但是如何在这里设置用户名？

Answer 1

您可以像这样使用 JPQL

@Override
public Account findAccount(String userName) {
  return em.createQuery("select account from Account account where account.username = :username", Account.class)
        .setParameter("username", userName).getSingleResult();
}

Answer 2

试试这个方法

    CriteriaBuilder criteriaB = entityManager.getCriteriaBuilder();
    CriteriaQuery<Distance> criteriaQ = criteriaB.createQuery(Account.class);

    Root<Account> element = criteriaQ.from(Account.class);

    Predicate[]predicates = new Predicate[1];
    predicates[0]= criteriaB.equal(element.get("userName"),userName); 

    criteriaQ.multiselect(element.get(Account)).where(predicates);

    return entityManager.createQuery(criteriaQ).getSingleResult();