C＃实体框架“在表上引入FOREIGN KEY约束可能会导致循环或多个级联路径

Question

我对该级联的工作方式有些困惑。所以我将这两个实体链接在一起。

销售合同：

public class SalesContract : ObjectMapper
{
    [Key]
    [Index(IsUnique = true)]
    [AutoGenerated]
    public Guid ID { get; set; } = Guid.NewGuid();

    [Required]
    [Index(IsUnique = true)]
    [StringLength(50)]
    public string SCNo { get; set; }

    [Required]
    public string DeliveryAddress { get; set; }

    public DateTime DeliveryDate { get; set; } = DateTime.UtcNow;

    [Required]
    public string Transport { get; set; }

    [ForeignKey("PaymentMethod")]
    public Guid PaymentMethodId { get; set; }
    public virtual PaymentMethod PaymentMethod { get; set; }

    public int PaymentTime { get; set; }

    public string Note { get; set; }

    [ForeignKey("ItemType")]
    public Guid ItemTypeId { get; set; }
    public ItemType ItemType { get; set; }

    public Guid SalesId { get; set; }
    public virtual Account Sales { get; set; }

    [ForeignKey("Buyer")]
    public Guid BuyerId { get; set; }
    public virtual Buyer Buyer { get; set; }

    [Required]
    public string Status { get; set; } = "Pending"; //Pending / Approved

    public Guid? ApprovedById { get; set; }
    public virtual Account ApprovedBy { get; set; }

    public bool? IsApproved { get; set; }

    [AutoGenerated]
    public DateTime DateCreated { get; set; } = DateTime.UtcNow;

    public ICollection<SalesContractItem> Items { get; set; }

    public async Task<bool> Delete(MigrationDBContext db)
    {
        this.Items.ForEach(m => { db.SalesContractItems.Remove(m); });
        db.SalesContracts.Remove(this);
        await db.SaveChangesAsync();
        return true;
    }
}

和销售合同项目：

public class SalesContractItem : ObjectMapper
{
    [Key]
    [Index(IsUnique = true)]
    [AutoGenerated]
    public Guid ID { get; set; } = Guid.NewGuid();

    [ForeignKey("Item")]
    public Guid ItemId { get; set; }
    public virtual Item Item { get; set; }

    [ForeignKey("Color")]
    public Guid ColorId { get; set; }
    public virtual Color Color { get; set; }

    [ForeignKey("Unit")]
    public Guid UnitId { get; set; }
    public virtual Unit Unit { get; set; }

    [ForeignKey("ItemType")]
    public Guid ItemTypeId { get; set; }
    public virtual ItemType ItemType { get; set; }

    public decimal Price { get; set; }
    
    [ForeignKey("Currency")]
    public Guid CurrencyId { get; set; }
    public Currency Currency { get; set; }

    [Required]
    public decimal BaseQty { get; set; }
    public decimal Remaining { get; set; }

    public string Description { get; set; }

    [AutoGenerated]
    public DateTime DateCreated { get; set; } = DateTime.UtcNow;

    [ForeignKey("SalesContract")]
    public Guid SalesContractId { get; set; }
    public virtual SalesContract SalesContract { get; set; }

    public async Task<bool> Delete(MigrationDBContext db)
    {
        db.SalesContractItems.Remove(this);
        await db.SaveChangesAsync();
        return true;
    }
}

ObjectMapper类仅包含函数，没有实体属性。

完整的错误消息是这样的：

在表'SalesContractItems'上引入FOREIGN KEY约束'FK_dbo.SalesContractItems_dbo.SalesContracts_SalesContractId'可能会导致循环或多个级联路径。指定ON DELETE NO ACTION或ON UPDATE NO ACTION，或修改其他FOREIGN KEY约束。 无法创建约束或索引。查看先前的错误。

这两个实体在删除时会导致多个级联是怎么回事？

---

注意

根据要求，这些是链接到两者的完整实体。

public class Item : ObjectMapper
{
    [Key]
    [Index(IsUnique = true)]
    [AutoGenerated]
    public Guid ID { get; set; } = Guid.NewGuid();

    [Required]
    [Index(IsUnique = true)]
    [StringLength(50)]
    public string ItemName { get; set; }

    public async Task<bool> Delete(MigrationDBContext db)
    {
        db.Items.Remove(this);
        await db.SaveChangesAsync();
        return true;
    }
}

public class Color : ObjectMapper
{
    [Key]
    [Index(IsUnique = true)]
    [AutoGenerated]
    public Guid ID { get; set; } = Guid.NewGuid();

    [Required]
    [Index(IsUnique = true)]
    [StringLength(50)]
    public string ColorCode { get; set; }

    public string ColorName { get; set; }

    public async Task<bool> Delete(MigrationDBContext db)
    {
        db.Colors.Remove(this);
        await db.SaveChangesAsync();
        return true;
    }
}

public class Unit : ObjectMapper
{
    [Key]
    [Index(IsUnique = true)]
    [AutoGenerated]
    public Guid ID { get; set; } = Guid.NewGuid();

    [Required]
    [Index(IsUnique = true)]
    [StringLength(50)]
    public string UnitName { get; set; }

    public async Task<bool> Delete(MigrationDBContext db)
    {
        db.Units.Remove(this);
        await db.SaveChangesAsync();
        return true;
    }
}

public class ItemType : ObjectMapper
{
    [Key]
    [Index(IsUnique = true)]
    [AutoGenerated]
    public Guid ID { get; set; } = Guid.NewGuid();

    [Required]
    [Index(IsUnique = true)]
    [StringLength(50)]
    public string ItemTypeName { get; set; }

    public async Task<bool> Delete(MigrationDBContext db)
    {
        db.ItemTypes.Remove(this);
        await db.SaveChangesAsync();
        return true;
    }
}

public class PaymentMethod : ObjectMapper
{
    [Key]
    [Index(IsUnique = true)]
    [AutoGenerated]
    public Guid ID { get; set; } = Guid.NewGuid();

    [Required]
    public string PaymentMethodName { get; set; }

    public async Task<bool> Delete(MigrationDBContext db)
    {
        db.PaymentMethods.Remove(this);
        await db.SaveChangesAsync();
        return true;
    }
}

public class Currency : ObjectMapper
{
    [Key]
    [Index(IsUnique = true)]
    [AutoGenerated]
    public Guid ID { get; set; } = Guid.NewGuid();

    [Required]
    [Index(IsUnique = true)]
    [StringLength(50)]
    public string CurrencyName { get; set; }

    [Required]
    public string CurrencySymbol { get; set; }

    public async Task<bool> Delete(MigrationDBContext db)
    {
        db.Currencies.Remove(this);
        await db.SaveChangesAsync();
        return true;
    }
}