在表上引入外键约束可能会导致循环或多个级联路径

Question

我已经发现了许多其他类似问题，但是我不确定为什么要在我的实体上这样做。 用下面的简单英语表示。 三个实体，帐户，站点和合同。 一个帐户可以有多个站点。 一个帐户可以有多个合同。 一个站点可以有多个合同。 因此，在某些情况下，您可以将合同附加到站点，然后将其附加到帐户，或者将合同直接附加到帐户。

我假设我正在这样做，因为有两种可能的级联用于删除合同，它要么在删除帐户时级联，然后直接附加到帐户，要么在删除站点时级联。

我认为合同中既不需要AccountId也不需要SiteId，因此这不会触发错误。 我想要做的是将合同附加到站点（然后是帐户），或者将合同直接附加到帐户-但是我仍然想保持数据库参照完整性。

Introducing FOREIGN KEY constraint 'FK_dbo.Contract_dbo.Site_SiteId' on table 'Contract' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.

我的课程/实体：

帐户

public partial class Account
{
    public int Id { get; set; }

    [Display(Name = "Account Name")]
    [Required]
    [MinLength(3, ErrorMessage = "The Account Name should be at least 3 characters")]
    [MaxLength(40, ErrorMessage = "The Account Name should be no more than 40 characters")]
    [Remote("IsAccountNameAvailable", "Helper", ErrorMessage = "This Account name already exists, please try another name")]
    public string AccountName { get; set; }

    [ScaffoldColumn(false)]
    [Display(Name = "Date Account Added")]
    public DateTime DateAdded { get; set; }

    public virtual ICollection<Site> Sites { get; set; }
    public virtual ICollection<Contract> Contracts { get; set; }
}

现场

public partial class Site
{
    public int Id { get; set; }

    [Required(ErrorMessage = "A site must be attached to an account - please specify an account")]
    [Display(Name = "Parent Account")]
    public int AccountId { get; set; }

    [Display(Name = "Site Name")]
    [Required]
    [MinLength(3, ErrorMessage = "The Site Name should be at least 3 characters")]
    [MaxLength(40, ErrorMessage = "The Site Name should be no more than 40 characters")]
    public string SiteName { get; set; }

    [ScaffoldColumn(false)]
    public DateTime DateAdded { get; set; }

    [Required]
    [Display(Name = "Primary Site")]

    //[Remote("IsThereAlreadyAPrimarySite", "Helper", AdditionalFields = "AccountId", ErrorMessage = "There is already a primary site set for this account", HttpMethod = "POST")]
    public bool PrimarySite { get; set; }

    [Display(Name = "Site Notes")]
    [Column(TypeName = "text")]
    public string SiteNotes { get; set; }

    public virtual Account Account { get; set; }

    public virtual ICollection<Contract> Contracts { get; set; }

}

合同

public partial class Contract
{
    public int Id { get; set; }

    public int AccountId { get; set; }
    public int SiteId { get; set; }

    [Display(Name = "Contract Type")]
    [Required]
    public int ContractTypeId { get; set; }

    public virtual Account Account { get; set; }

    public virtual Site Site { get; set; }

    public virtual ContractType ContractType { get; set; }

}

Answer 1

在您的DbContext文件覆盖方法OnModelCreating中，必须至少配置一个关系，以便在删除时不进行级联。 删除时必须明确处理该关系

protected override void OnModelCreating( DbModelBuilder modelBuilder )
{
    base.OnModelCreating( modelBuilder );

    modelBuilder.Entity<Contract>()
        .HasRequired( c => c.Site)
        .WithMany( s => s.Contracts )
        .WillCascadeOnDelete( false );
}