如何从双向多对多关联中删除孩子？

Question

如何从双向多对多关联中删除子项？

删除孩子不起作用，因为我遇到异常（FK Violation）。

只是从父级中删除子级并在父级上调用 saveorupdate 不会做任何事情。

实体：

public class Employee : Entity
{
    public virtual string LastName { get; set; }
    public virtual string FirstName { get; set; }
    public virtual string EMail { get; set; }
    public virtual IList<LoanedItem> LoanedItems { get; set; }
    public virtual ISet<Team> Teams { get; set; }

    public Employee()
    {
        if (LoanedItems == null)
        {
            LoanedItems = new List<LoanedItem>();
        }

        if (Teams == null)
        {
            Teams = new HashedSet<Team>();
        }
    }

    public virtual void AddTeam(Team team)
    {
        Teams.Add(team);
        team.Employees.Add(this);
    }

    public virtual void RemoveTeamFromEmployee(Team team)
    {
        Teams.Remove(team);
    }
}

public class Team : Entity
{
    public virtual string Name { get; set; }
    public virtual ISet<Employee> Employees { get; set; }

    public Team()
    {
        if (Employees == null)
        {
            Employees = new HashedSet<Employee>();
        }
    }

    public virtual void RemoveEmployeeFromTeam (Employee employee)
    {
        var result = Employees.Remove(employee);
    }

    public virtual void AddEmployee(Employee employee)
    {
        Employees.Add(employee);
        employee.Teams.Add(this);
    }
}

映射：

public class TeamMap : ClassMap<Team>
{
    public TeamMap()
    {
        // identity mapping
        Id(p => p.Id)
            .Column("TeamId")
            .GeneratedBy.Identity();

        // column mapping
        Map(p => p.Name);

        // Employee is responible for the relationship
        HasManyToMany(p => p.Employees)
            .Table("TeamEmployee")
            .AsSet()
            .LazyLoad()
            .Inverse()
            .Cascade.SaveUpdate()
            .ParentKeyColumn("TeamId")
            .ChildKeyColumn("EmployeeId")
            .NotFound.Ignore();

    }
}

public class EmployeeMap : ClassMap<Employee>
{
    public EmployeeMap()
    {
        // identifier mapping
        Id(p => p.Id)
            .Column("EmployeeId")
            .GeneratedBy.Identity();

        // column mapping
        Map(p => p.EMail);
        Map(p => p.LastName);
        Map(p => p.FirstName);

        // Employee is responible for the relationship
        HasManyToMany(p => p.Teams)
            .Table("TeamEmployee")
            .AsSet()
            .LazyLoad()
            .ParentKeyColumn("EmployeeId")
            .ChildKeyColumn("TeamId")
            .Cascade.SaveUpdate()
            .NotFound.Ignore();

        HasMany(p => p.LoanedItems)
            .Cascade.SaveUpdate()
            .KeyColumn("EmployeeId");
    }
}

编辑

删除团队的代码：

//Test Case 2
//Delete Team 2
Team team = session.Get<Team>(2);

List<Employee> employees = team.Employees.ToList();

foreach (var employee in employees)
{
    team.RemoveEmployeeFromTeam(employee);
}

session.Delete(team);

Answer 1

如果是多对多，那么一个方向就是“主”方向。另一个方向将定义inverse="false"。您必须以正确的方式从集合中删除 - 确保（并真正代表您的删除所达到的效果），删除两者。然后刷新会话以使其保持不变。

例子：

如果A 具有B 类型的对象集合，反之亦然，那么要删除两个特定实例之间的关联，您必须从B 集合的实例反之亦然。然后当会话被刷新时，NHibernate 知道从链接表中删除相关行。

现在编辑你已经发布的代码

尝试像这样更改这两种方法：

public virtual void RemoveTeamFromEmployee(Team team)
{
    Teams.Remove(team);
    team.Employees.Remove(this);
}

public virtual void RemoveEmployeeFromTeam (Employee employee)
{
    Employees.Remove(employee);
    employee.Teams.Remove(this);
}

要整理代码以删除不对关系负责的团队，您必须遍历链接的员工。但是，如果您必须比员工更频繁地删除团队，那么您可能会发现反转它更方便，然后您可以使用：

team.Employees.Clear();
session.Delete(team);