实体框架4.1 Codefirst:删除一对多子项时出现"给定多重性约束"错误

Question

我在Entity Framework 4.1中有以下类(这些类已被修剪以保持代码可读)

public class MetaInformation
{
    public int Id { get; set; }
    public virtual MetaInformationObject RelatedTo { get; set; }
}

public abstract class MetaInformationObject
{
    public int Id { get; set; }
    public virtual List<MetaInformation> MetaInformations { get; set; }
}

[Table("Hardwares")]
public class Hardware : MetaInformationObject
{
    [MaxLength(100)]
    public string Name { get; set; }
}

public class Inventory
{
    public int Id { get; set; }
    public virtual List<Machine> Machines { get; set; }
}

public class Machine : Hardware
{
    public Inventory Inventory { get; set; }
}

 protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Isis.Business.Base.MetaInformationObject>()
        .HasMany<Isis.Business.Base.MetaInformation>(mi => mi.MetaInformations).WithRequired(mi => mi.RelatedTo).WillCascadeOnDelete(true);
    modelBuilder.Entity<Isis.Business.Inventory.Inventory>()
            .HasMany<Isis.Business.Inventory.Machine>(i => i.Machines).WithRequired(m => m.Inventory).WillCascadeOnDelete(true);

    base.OnModelCreating(modelBuilder);
}

---

有一次,我想更新机器信息,所以如果它已经存在于数据库中,我加载它,附加它然后清除以前的元信息以用新的元信息替换它们.

public void UpdateMachine(Inventory i, Machine m)
{
    DataContext.Dao.Db.Inventories.Attach(i);
    if (!i.Machines.Exists(InnerHardware => InnerHardware.SerialNumber == m.SerialNumber)) {
        i.Machines.Add(m);
    } else {
        var workingMachine = i.Machines.First(Machine => Machine.SerialNumber == m.SerialNumber);
        Dao.Db.Machines.Attach(workingMachine);
        if (workingMachine.MetaInformations != null && workingMachine.MetaInformations.Count > 0) {
            workingMachine.MetaInformations.Clear();
            //workingMachine.MetaInformations.ForEach(mi => { Dao.Db.MetaInformations.Attach(mi); Dao.Db.MetaInformations.Remove(mi); }); // tried this to, with variations
        }
        workingMachine.MetaInformations = m.MetaInformations;
    }
    DataContext.Dao.Db.SaveChanges();
}

然后,抛出以下DbUpdateException:

来自'MetaInformationObject_MetaInformations'AssociationSet的关系处于'已删除'状态.给定多重约束,相应的'MetaInformationObject_MetaInformations_Target'也必须处于'已删除'状态.

我试过所以要解决这里的问题下面的一些问题,特别是尝试读取这个和链接(这就是为什么有一个直接引用的原因在回答中提供MetaInformation给MetaInformationObject),但我无法弄清楚什么是错的.

Answer 1

级联删除在这里不会帮助你.只有删除父实体(MetaInformationObject)时才会进行级联删除.这里的问题是在相关对象的集合上调用Clear不会删除它们.它只删除关系(=它将外键设置MetaInformation为null)但映射约束不允许(您根据需要定义了关系).避免这种情况的方法是:

• 迭代所有相关的MetaInformations并删除它们中的每一个
• 重构您的模型以定义识别关系.之后,Clear不仅会破坏关系,还会将相关实体标记为已删除.