C#•10mo ago

✅ EF Core 8.0.3 Many To Many Relation

quick question, im using entity framework core(8.0.3) code first approach: I have 2 classes (many to many relation):

[PrimaryKey(nameof(Id), nameof(SecondId))]
public class A
{
  public string Id { get; set; }
  public string SecondId { get; set; }

  public virtual ICollection<B> Bs;

  public A()
  {
    Bs = new HashSet<B>();
  }
}

[PrimaryKey(nameof(Id), nameof(SecondId))]
public class A
{
  public string Id { get; set; }
  public string SecondId { get; set; }

  public virtual ICollection<B> Bs;

  public A()
  {
    Bs = new HashSet<B>();
  }
}

public class B
{
  [Key]
  public string Id { get; set; }

  public virtual ICollection<A> As;

  public B()
  {
    As = new HashSet<A>();
  }
}

public class B
{
  [Key]
  public string Id { get; set; }

  public virtual ICollection<A> As;

  public B()
  {
    As = new HashSet<A>();
  }
}

It's automatically creating the "third" table and on first entry its filling it aswell. Now the first time I add some new stuff it works fine. If I get the same Identifier tho it crashes, is there a way to automatically resolve it? or do I have to check if existing then add into table otherwise add to list?

b.As.Add(new A());

b.As.Add(new A());

Thanks in advance!

4 Replies

Angius•10mo ago

EF's support of hashsets is meh at best

MyridorOP•10mo ago

So i should ignore them and fill all tables by myself?

Angius•10mo ago

The issue probably stems from the fact, that you create a duplicate entry on the join table I'd just use

public class A
{
  public string Id { get; set; }
  public string SecondId { get; set; }
  public List<B> Bs { get; set; } = [];
}

public class B
{
  public string Id { get; set; }
  public List<A> As { get; set; } = [];
}

public class A
{
  public string Id { get; set; }
  public string SecondId { get; set; }
  public List<B> Bs { get; set; } = [];
}

public class B
{
  public string Id { get; set; }
  public List<A> As { get; set; } = [];
}

Also, not sure if your code is actually the code you use, but your navigation properties weren't properties So that would be an issue for EF as well

Unknown User•10mo ago

Message Not Public

Gaming

Programming

✅ EF Core 8.0.3 Many To Many Relation