实体框架迁移级联删除警告

Question

I have two classes that relate to one another (one-to-many) and I thought I had the properties setup correctly, but when I run the Update-Database command for my migration, I get the following error:

Introducing FOREIGN KEY constraint 'FK_dbo.ParentEnrollment_dbo.CellGroup_CellGroupID' on table 'ParentEnrollment' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint or index. See previous errors.

My two classes:

[Table("CellGroup")]
public class CellGroup : BaseEntity
{
    public Guid AcademicYearID { get; set; }

    [ForeignKey("AcademicYearID")]
    public virtual AcademicYear AcademicYear { get; set; }

    public Guid LeaderID { get; set; }

    [ForeignKey("LeaderID")]
    public virtual Parent Leader { get; set; }

    public Guid PreviousGroupID { get; set; }

    [ForeignKey("PreviousGroupID")]
    public virtual CellGroup PreviousGroup { get; set; }

    public string Name { get; set; }

    public int MaximumSize { get; set; }

    public virtual ICollection<ParentEnrollment> Parents { get; set; }
}

and

[Table("ParentEnrollment")]
public class ParentEnrollment : BaseEntity
{
    public Guid ParentID { get; set; }

    [ForeignKey("ParentID")]
    public virtual Parent Parent { get; set; }

    public Guid AcademicYearID { get; set; }

    [ForeignKey("AcademicYearID")]
    public virtual AcademicYear AcademicYear { get; set; }

    public bool FirstTimeEnrolling { get; set; }

    public string HSLDAAccountNumber { get; set; }

    public DateTime HSLDARenewalDate { get; set; }

    public string CurrentChurch { get; set; }

    public string CurrentChurchContact { get; set; }

    public string CurrentChurchPhone { get; set; }

    public Guid CellGroupID { get; set; }

    [Required]
    [ForeignKey("CellGroupID")]
    public virtual CellGroup CellGroup { get; set; }

    public bool VolunteerBuyOut { get; set; }

    public Guid VolunteerPositionID { get; set; }

    [ForeignKey("VolunteerPositionID")]
    public virtual VolunteerPosition VolunteerPosition { get; set; }

    public string VolunteerPositionNotes { get; set; }

    public virtual ICollection<StudentEnrollment> StudentEnrollments { get; set; }
}

I only have the Parents property on the CellGroup class so I can easily access the list of enrollments in that cell group. I tried to remove the property to see if it cleared up the warning/error, but it did not. Can someone spot where I have gone wrong with my model(s)?

Answer 1

This error says that you cannot introduce a foreign key from table ParentEnrollment to table CellGroup that has cascading delete enabled, because this will create multiple cascade paths, which is not allowed on SQL Server.

According to the code you posted both tables have relations to a table Parent as well as AcademicYear , which are on non nullable FK columns, so EF will enable cascading on delete by default. With another FK from ParentEnrollment to CellGroup there would be multiple cascade paths, eg Parent to CellGroup to ParentEnrollment and Parent to ParentEnrollment , and this is causing your error. Removing the Parent property won't solve this because there still is the same cascading path problem starting from table AcademicYear .

So you have to disable cascading delete for your foreign key, which has to be done using Fluent API in your DbContext like this:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);
    modelBuilder.Entity<ParentEnrollment>()
                .HasRequired(m => m.CellGroup)
                .WithMany(m => m.Parents)
                .HasForeignKey(m => m.CellGroupID)
                .WillCascadeOnDelete(false);
}