Entity Framework Core 3.1 Code-First Model - 定义与 self 具有多个多对多关系的 model

Question

I like to create a DB model in ASP.Net Core 3.1. I am using Code First approach with EF Core 3.1.

I like to create a model for this relationship-

So, there is one Employee table and every employee has multiple bosses and each has multiple sub-ordinates. But every boss and every subordinate are employees also. What I have done is something like this-

Employee Model-

public class Employee
{
    [HiddenInput(DisplayValue = false), Display(Name = "ID")]
    [Key()]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [Column(Order = 1)]
    public Guid? Id { get; set; } = Guid.NewGuid();

    [Column("Name"), Required(ErrorMessage = "Term Name should be given"), Display(Name = "Term Name", Prompt = "Please Give Term Name")]
    [DataType(DataType.Text)]
    public string Name { get; set; }

    public ICollection<Boss> Bosses { get; set; }
    public ICollection<Subordinate> Subordinates { get; set; }
    ............
    ............
}

But I am getting this error during creating the DB model by the command Add-Migration <MigrationName> -

Unable to determine the relationship represented by navigation property 'Employee.Bosses' of type 'ICollection'. Either manually configure the relationship, or ignore this property using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.

Can anyone please help?

Answer 1

direct many-to-many relations are not supported with ef core 3.1.

See this: https://docs.microsoft.com/de-de/ef/core/what-is-new/ef-core-5.0/whatsnew

If you cannot use ef core >= 5, than you have to create a navigation property to the EmployeeBoss entity.

Answer 2

Try this:

 public partial class Employee
    {
        public Employee()
        {
            EmployeeBossEmployees = new HashSet<EmpoyeeBoss>();
            EmployeeBossBosses = new HashSet<EmpoyeeBoss>();
        }

        [Key]
        public int Id { get; set; }

        [InverseProperty(nameof(EmpoyeeBoss.Employee))]
        public virtual ICollection<EmpoyeeBoss> EmployeeBossEmployees { get; set; }
        [InverseProperty(nameof(EmpoyeeBoss.Boss))]
        public virtual ICollection<EmpoyeeBoss> EmployeeBossBosses { get; set; }
    }

 public partial class EmpoyeeBoss
    {
        [Key]
        public int Id { get; set; }
        public int BossId { get; set; }
        public int EmployeeId { get; set; }

        [ForeignKey(nameof(EmployeeId))]
        [InverseProperty("EmployeeBossEmployees")]
        public virtual Employee Employee { get; set; }
        [ForeignKey(nameof(BossId))]
        [InverseProperty("EmployeeBossBosses")]
        public virtual Employee Boss { get; set; }
    }

and include in your dbcontext:

        public virtual DbSet<Employee> Employees { get; set; }
        public virtual DbSet<EmpoyeeBoss> EmployeeBosses { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<EmpoyeeBoss>(entity =>
            {
                entity.HasOne(d => d.Employee)
                    .WithMany(p => p.EmployeeBossEmployees)
                    .HasForeignKey(d => d.EmployeeId)
                    .OnDelete(DeleteBehavior.ClientSetNull);
                   

                entity.HasOne(d => d.Boss)
                    .WithMany(p => p.EmployeeBossBosses)
                    .HasForeignKey(d => d.BossId);
                   
            });