c# – NHibernate – 如何从多对多关系中删除项目？

我跟踪两个表之间的映射,它们之间具有多对多关系.如何从映射表中删除一个条目,在我的情况下是“ProjectUser”？

public ProjectMap()
{
    Id(x => x.Id);
    Map(x => x.ProjectName);
    Map(x => x.Description);
    References<User>(x => x.Owner);
    HasManyToMany(x => x.Users)
        .Cascade.SaveUpdate()
        .Table("ProjectUser")
        .Not.LazyLoad();
}


public UserMap()
{
    Id(x => x.Id);
    Map(x => x.FirstName);
    Map(x => x.LastName);
    Map(x => x.UserName);
    HasManyToMany(x => x.Projects)
        .Cascade.SaveUpdate()
        .Inverse()
        .Table("ProjectUser")
        .Not.LazyLoad();
}

编辑：按照答案中的建议将Cascade更改为SaveUpdate.这是我用来将数据提交到SQLite数据库的代码.

using (var trans = session.BeginTransaction())
{
    var existingUsers = project.Users.ToList();
    foreach (var item in existingUsers)
    {
        if (selectedUsers.Count(x => x.Id == item.Id) == 0)
            project.Users.RemoveAt(project.Users.IndexOf(item));
    }
    session.SaveOrUpdate(project); // This fixed the issue
    session.Flush();
    foreach (var item in selectedUsers)
    {
        if (project.Users.Count(x => x.Id == item.Id) == 0)
        {
            project.AddUser(session.Get<User>(item.Id));
        }
    }
    session.SaveOrUpdate(project);
    session.Flush();
    trans.Commit();
}

// Add user code in Project class
public virtual void AddUser(User userToAdd)
{
    if (this.Users == null)
        this.Users = new List<User>();
    userToAdd.Projects.Add(this);
    this.Users.Add(userToAdd);
}

每当我尝试保存/更新时,我都会收到以下错误：

a different object with the same identifier value was already associated with the session: 10, of entity: Models.Project

EDIT2：应使用session.SaveOrUpdate(项目)和session.Flush()来避免上述错误.

解决方法:

如果您只想删除ProjectUser条目而不是实际删除另一侧的实体,则需要从Cascade.All()更改为Cascade.SaveUpdate().

目前,如果您从项目中删除了用户并保存了项目,则会删除ProjectUser条目和User对象.

标签：c,nhibernate,fluent-nhibernate,nhibernate-mapping,fluent-nhibernate-mapping
来源： https://codeday.me/bug/20190613/1234220.html