Question

我遇到了这个问题但无法解决。

我想实现OneToMany / ManyToOne映射而不创建额外的表。

我有两个实体：

（1）Employee.java

@Entity(name="EMPLOYEE_DETAILS")
public class Employee {
  private int empId;    
  private String employeeName;
  private Date joiningDate;

  private Collection<Project> project = new ArrayList<Project>();

  @Id
  @GeneratedValue (strategy = GenerationType.AUTO)
  public int getEmpId() {
        return empId;
  }
  public void setEmpId(int employeeId) {
        this.empId = employeeId;
  }

  public String getEmployeeName() {
        return employeeName;
  }
  public void setEmployeeName(String employeeName) {
        this.employeeName = employeeName;
  }

  @Temporal (TemporalType.DATE)
  public Date getJoiningDate() {
        return joiningDate;
  }
  public void setJoiningDate(Date joiningDate) {
        this.joiningDate = joiningDate;
  }

  @OneToMany(mappedBy="employeeObj")
  public Collection<Project> getProject() {
        return project;
  }
  public void setProject(Collection<Project> project) {
        this.project = project;
  }
 }

（2）Project.java

@Entity
public class Project {
@Id
@GeneratedValue (strategy = GenerationType.AUTO)
private int projectId;
private String projectName;

@ManyToOne
@JoinColumn(name="EMPLOYEE_ID")
private Employee employeeObj;

public int getProjectId() {
    return projectId;
}
public void setProjectId(int projectId) {
    this.projectId = projectId;
}
public String getProjectName() {
    return projectName;
}
public void setProjectName(String projectName) {
    this.projectName = projectName;
}
public Employee getEmployeeObj() {
    return employeeObj;
}
public void setEmployeeObj(Employee employeeObj) {
    this.employeeObj = employeeObj;
}

}

我有一个主要课程：

（3）MainClass.java

public class MainClass {

public static void main(String[] args) {
    Collection<Project> collection = new ArrayList<Project>();

    Project projectA = new Project();
    projectA.setProjectName("ABC");

    Project projectB = new Project();
    projectB.setProjectName("DEF");

    collection.add(projectA);
    collection.add(projectB);

    Employee employee = new Employee();
    employee.setEmployeeName("Swarup Saha");
    employee.setJoiningDate(new Date());

    employee.setProject(collection);

    //Many To One Configuration
    projectA.setEmployeeObj(employee);
    projectB.setEmployeeObj(employee);

    Configuration configuration = new Configuration().configure();
    StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder().
    applySettings(configuration.getProperties());
    SessionFactory factory = configuration.buildSessionFactory(builder.build());

    Session session = factory.openSession();
    session.beginTransaction();
    session.save(employee);
    session.save(projectA);
    session.save(projectB);

    session.getTransaction().commit();
    session.close();
    factory.close();         
}
}

当我运行这个时，我在控制台中遇到了这个问题。

ERROR: Table 'project' already exists
Hibernate: alter table Project add constraint FK_aj4dhrm7m2sit4f8tcimf1121         foreign key (EMPLOYEE_ID) references EMPLOYEE_DETAILS (empId)
Mar 25, 2015 12:39:29 AM org.hibernate.tool.hbm2ddl.SchemaExport perform
ERROR: HHH000389: Unsuccessful: alter table Project add constraint  FK_aj4dhrm7m2sit4f8tcimf1121 foreign key (EMPLOYEE_ID) references   EMPLOYEE_DETAILS (empId)
Mar 25, 2015 12:39:29 AM org.hibernate.tool.hbm2ddl.SchemaExport perform
ERROR: Key column 'EMPLOYEE_ID' doesn't exist in table
Mar 25, 2015 12:39:29 AM org.hibernate.tool.hbm2ddl.SchemaExport execute
INFO: HHH000230: Schema export complete
Hibernate: insert into EMPLOYEE_DETAILS (employeeName, joiningDate) values (?, ?)
Hibernate: insert into Project (EMPLOYEE_ID, projectName) values (?, ?)
Mar 25, 2015 12:39:30 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper  logExceptions
WARN: SQL Error: 1054, SQLState: 42S22
Mar 25, 2015 12:39:30 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptions 
ERROR: Unknown column 'EMPLOYEE_ID' in 'field list'
Mar 25, 2015 12:39:30 AM  org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: SQL Warning Code: 1054, SQLState: 42S22
Mar 25, 2015 12:39:30 AM org.hibernate.engine.jdbc.spi.SqlExceptionHelper$StandardWarningHandler logWarning
WARN: Unknown column 'EMPLOYEE_ID' in 'field list'
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column 'EMPLOYEE_ID' in 'field list'

有什么建议我在这做错了什么？

Answer 1

代码中没有问题。我从数据库中删除了所有表，然后运行MainClass并且程序运行成功。：d

 Hibernate: alter table Project drop foreign key  FK_p6ig2lkv4igor3itfy6v11sy4
 Mar 25, 2015 11:35:09 PM org.hibernate.tool.hbm2ddl.SchemaExport perform
 ERROR: HHH000389: Unsuccessful: alter table Project drop foreign key FK_p6ig2lkv4igor3itfy6v11sy4
 Mar 25, 2015 11:35:09 PM org.hibernate.tool.hbm2ddl.SchemaExport perform
 ERROR: Table 'hibernatedb.project' doesn't exist 
 Hibernate: drop table if exists EMPLOYEE_DETAILS
 Hibernate: drop table if exists Project
 Hibernate: create table EMPLOYEE_DETAILS (EMP_ID integer not null auto_increment, employeeName varchar(255), joiningDate date, primary key (EMP_ID))
 Hibernate: create table Project (projectId integer not null auto_increment, projectName varchar(255), EMP_ID integer not null, primary key (projectId))
 Hibernate: alter table Project add constraint FK_p6ig2lkv4igor3itfy6v11sy4 foreign key (EMP_ID) references EMPLOYEE_DETAILS (EMP_ID)
 Mar 25, 2015 11:35:09 PM org.hibernate.tool.hbm2ddl.SchemaExport execute
 INFO: HHH000230: Schema export complete
 Hibernate: insert into EMPLOYEE_DETAILS (employeeName, joiningDate) values (?, ?)
 Hibernate: insert into Project (EMP_ID, projectName) values (?, ?)
 Hibernate: insert into Project (EMP_ID, projectName) values (?, ?)
 Mar 25, 2015 11:35:09 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
 INFO: HHH000030: Cleaning up connection pool [jdbc:mysql://localhost/hibernateDB]

Hibernate：com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException：'字段列表'中的未知列

1 个答案: