使用Fluent NHibernate自动映射创建多个双向一对多关联

我对NHibernate和.NET框架还比较陌生。

我想映射我的项目类,它有一对多关系子项目和项目任务类。

public class Project : ProjectItem
{
    public virtual IList<Subproject> Subprojects { get; set; }

    public virtual IList<ProjectTask> Tasks { get; set; }

    [NotNull]
    public virtual ProjectStatus Status { get; set; }

    public Project()
    {
        Subprojects = new List<Subproject>();
        Tasks = new List<ProjectTask>();
        Status = new ProjectStatus();
    }

    public virtual void AddSubProject(Subproject subproject)
    {
        subproject.Project = this;
        Subprojects.Add(subproject);
    }

    public virtual void RemoveSubProject(Subproject subproject)
    {
        Subprojects.Remove(subproject);
    }

    public virtual void AddTask(ProjectTask task)
    {
        task.Project = this;
        Tasks.Add(task);
    }

    public virtual void RemoveTask(ProjectTask task)
    {
        Tasks.Remove(task);
    }
}

public class ProjectTask : ProjectItemTask
{
    [NotNull]
    public virtual Project Project { get; set; }
}

public class Subproject : ProjectItem
{
    [NotNull]
    public virtual Project Project { get; set; }
}

我的实体从抽象基类继承Id属性。

我使用自动映射覆盖重新定义映射:

public class ProjectMappingOverride : IAutoMappingOverride<Project>
{
    public void Override(AutoMapping<Project> mapping)
    {
        mapping.HasMany<Subproject>(x => x.Subprojects)
            .Cascade.All()
            .Inverse()
            .Not.LazyLoad()
            .AsBag();

        mapping.HasMany<ProjectTask>(x => x.Tasks)
            .Cascade.All()
            .Inverse()
            .Not.LazyLoad()
            .AsBag();

        mapping.HasOne<ProjectStatus>(x => x.Status)
            .Cascade.All()
            .Not.LazyLoad();
    }
}

public class SubprojectMappingOverride : IAutoMappingOverride<Subproject>
{
    public void Override(AutoMapping<Subproject> mapping)
    {
        mapping.References<Project>(x => x.Project)
            .ForeignKey("ProjectId");
    }
}

public class ProjectTaskMappingOverride : IAutoMappingOverride<ProjectTask>
{
    public void Override(AutoMapping<ProjectTask> mapping)
    {
        mapping.References<Project>(x => x.Project)
            .ForeignKey("ProjectId");
    }
}

当我只映射与子项目类的关联时,一切正常,并且Project中的子项目类的所有实例都将正确存储到数据库中。当我对ProjectTask类使用第二个重写时,出现以下异常:

--->NHibernate.hibernate异常:数据库中已存在名为“ProjectId”的对象。无法创建约束。请参阅以前的错误。

--->System.Data.SqlClient.SqlException:数据库中已存在名为“ProjectId”的对象。

有人知道为什么会这样吗?