无法创建唯一键约束

Question

我正在创建一个简单的实体，并试图将它持久化到Oracle数据库中。这是我的天赋:

import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.persistence.UniqueConstraint;

@Entity
@Table(name = "TBL_FLIGHT", uniqueConstraints = @UniqueConstraint(name = "flight_number", columnNames = {
        "comp_prefix", "flight_number" }))
public class Flight implements Serializable {
    @Id 
    private Long id;
    private String companyPrefix;
    private String number;

    public Long getId() {
        return id;
    }

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

    public void setCompanyPrefix(String companyPrefix) {
        this.companyPrefix = companyPrefix;
    }

    public void setNumber(String number) {
        this.number = number;
    }   

    @Column(name = "comp_prefix")
    public String getCompanyPrefix() {
        return companyPrefix;
    }

    @Column(name = "flight_number")
    public String getNumber() {
        return number;
    }
}

这是我的Java类，它创建了这个实体的一个实例，并使用HiberNate将其保存到数据库中：

public class AppTest{

    public static void main(String[] args) {

        Session session = HibernateUtil.getSessionFactory().getCurrentSession();
        session.beginTransaction();

        Flight flight = new Flight();
        flight.setCompanyPrefix("prefix");;
        flight.setNumber("100");
        flight.setId(1L);
        session.save(flight);

        session.getTransaction().commit();          

        HibernateUtil.getSessionFactory().close();
    }
}

当我运行这个程序时，我得到一个异常:

Caused by: org.hibernate.AnnotationException: Unable to create unique key constraint (comp_prefix, flight_number) on table TBL_FLIGHT: database column 'comp_prefix', 'flight_number' not found. Make sure that you use the correct column name which depends on the naming strategy in use (it may not be the same as the property name in the entity, especially for relational types)
    at org.hibernate.cfg.Configuration.buildUniqueKeyFromColumnNames(Configuration.java:1682)
    at org.hibernate.cfg.Configuration.buildUniqueKeyFromColumnNames(Configuration.java:1614)
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1450)
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1844)

请帮助我在此代码中犯错误的地方。我正在使用Hibernate-4.3.6

更新：这是我的Hibernate配置文件，表由Hibernate本身生成：

<session-factory>

    <!-- Database connection settings -->
    <property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
    <property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:XE</property>
    <property name="hibernate.connection.username">myuser</property>
    <property name="hibernate.connection.password">mypasswd</property>
    <property name="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</property>

    <!-- JDBC connection pool (use the built-in) -->
    <property name="connection.pool_size">1</property>

    <!-- Enable Hibernate's automatic session context management -->
    <property name="current_session_context_class">thread</property>

    <!-- Disable the second-level cache -->
    <property name="cache.provider_class">org.hibernate.cache.internal.NoCacheProvider</property>

    <!-- Echo all executed SQL to stdout -->
    <property name="show_sql">true</property>

    <!-- Drop and re-create the database schema on startup -->
    <property name="hbm2ddl.auto">update</property>

    <mapping class="org.hibernate.tutorial.Flight" />
</session-factory>

另外，如果可能的话，请给我推荐一个Hibernate-4.3的好资源，因为在线文档对于像我这样的初学者来说不是一个好的资源。

Answer 1

当我尝试在类 A 上的列“a_id”和“b_id”列上创建唯一约束并且我没有用 @ManyToOne 注释 B 时，问题出现在我身上，因此 Hibernate 对列“b_id”一无所知（作为类 B 的外键）：

   @Entity
   @Table(uniqueConstraints = { @UniqueConstraint(columnNames = { "a_id", "b_id" }) })
   Class A {
      @Id
      a_id;

      // @ManyToOne was not annotated
      B b;
   }

   @Entity
   Class B {
      @Id
      b_id
   }

Answer 2

您正在使用字段访问策略（由@Id注释确定）。将任何与JPA相关的注释放在每个字段的正上方，而不是getter属性

作为JPA提供者，Hibernate可以自省实体属性(实例字段)或访问器(实例属性)。默认情况下，@Id注释的位置提供了默认的访问策略。当放置在字段上时，Hibernate将假设基于字段的访问。放在标识符getter上，Hibernate将使用基于属性的访问

Answer 3

我也有同样的错误，通过显式设置@科列（name="field_name"）为@UniqueConstraint中使用的属性来解决。