C#•3mo 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•3mo ago

EF's support of hashsets is meh at best

Myridor•3mo ago

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

Angius•3mo 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•3mo ago

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✅ EF Core 8.0.3 Many To Many Relation