EF Core: Map Many to Many relationship without navigation property

Question

I'm trying to create a many to many relationship in entity Framework Core using Fluent API Here is my first model:

MyCalculationSelector.cs

  public int SortOrder { get; set; }
  public string UserString { get { return Name; } }

  private IList<CalculationType> _calculationTypes;
  public virtual IList<CalculationType> CalculationTypes
    {
       get { return _calculationTypes; }
       set { _calculationTypes = value; }
    }

And this is my second model:

MyCalculationType.cs

 public int SortOrder { get; set; }

 public string UserString
 {
    get { return Name; }
 }

 public int CalculationMethod { get; set; }

I remember that EF 6 could easily make the many to many relationship from Fluent API:

modelBuilder.Entity<MyCalculationSelector>().HasMany(x => x.MyCalculationTypes).WithMany();

Can we something like this be achieved in ef core? as of today, Hasmany-Withmany implementation is not possible

Answer 1

I have followed the documentation and have come up with this answer, please, someone who knows more than me and will correct me if I am wrong.

I first created my join table:

CalculationSelectorCalculationType.cs

public class CalculationSelectorCalculationType
    {
        public int CalculationSelector_Id { get; set; }
        public CalculationSelector CalculationSelector { get; set; }

        public int CalculationType_Id { get; set; }
        public CalculationType CalculationType { get; set; }
    }

CalculationSelector.cs

public CalculationSelector()
   {
      _calculationTypes = new List<CalculationSelectorCalculationType>();
      FontSize = 30;
   }
public int SortOrder { get; set; }
public string UserString { get { return Name; } }

private IList<CalculationSelectorCalculationType> _calculationTypes;
public virtual IList<CalculationSelectorCalculationType> CalculationTypes
    {
       get { return _calculationTypes; }
       set { _calculationTypes = value; }
    }

CalculationType.cs

 public int SortOrder { get; set; }

 public string UserString
 {
    get { return Name; }
 }

 public int CalculationMethod { get; set; }

...and finally my DbContext:

modelBuilder.Entity<CalculationSelectorCalculationType>().HasKey(p => new { p.CalculationSelector_Id, p.CalculationType_Id });
modelBuilder.Entity<CalculationSelectorCalculationType>().HasOne(p => p.CalculationSelector).WithMany(x => x.CalculationTypes).HasForeignKey(p => p.CalculationSelector_Id);
modelBuilder.Entity<CalculationSelectorCalculationType>().HasOne(p => p.CalculationType).WithMany().HasForeignKey(p => p.CalculationType_Id);

Answer 2

You can represent this with a private field or property:

modelBuilder.Entity<MyCalculationSelector>()
    .HasMany(x => x.MyCalculationTypes)
    .WithMany("NameOfThePrivateFieldOnMyCalculationType");

This way the navigation property is not exposed publically, but you can still use the Navigation Property on MyCalculationSelector without needing to traverse the intermediate join table.