违反了EF多重性约束。 关系的角色…具有多重性1或0..1

Question

I am getting the error

Multiplicity constraint violated. The role 'BegrotingsCategorie_children_Source' of the relationship 'NET.DAL.EF.BegrotingsCategorie_children' has multiplicity 1 or 0..1.

when trying to read a 'BegrotingsCategorie' from my database. This piece of code triggers the exception

 public BegrotingsCategorie ReadBegrotingsCategorie(int begrotingsCategorieId)
        {
            return _ctx.Begrotingscategorieen.Find(begrotingsCategorieId);
        }

My BegrotingsCategorie model looks like this

 [Table("tblBegrotingsCategorieen")]
    public class BegrotingsCategorie
    {
        [Key]
        public int BegrotingsCategorieId { get; set; }
        public string Informatie { get; set; }
        public double Uitgaven { get; set; }
        public Begroting Begroting { get; set; }
        public BegrotingsCategorie Parent { get; set; }
        public double Percentage { get; set; } 
        public double BerekendLoon { get; set; }

        public virtual ICollection<BegrotingsCategorie> children { get; set; }
        public virtual ICollection<Actie> Acties { get; set; }

    }

I have no idea how to solve this..

Edit Some rows in the database

database

The first row is the parent so its Parent_BegrotingsCategorieId is NULL, it has 1 child with Parent_BegrotingsCategorieId 1 who on its own also has multiple children so they have Parent_BegrotingsCategorieId 2

I add my data like this

public BegrotingsCategorie AddBegrotingsCategorie(string informatie, Begroting begroting, BegrotingsCategorie parentCategorie)
        {
            BegrotingsCategorie begrotingsCategorie = new BegrotingsCategorie()
            {
                Informatie = informatie,
                Begroting = begroting,
                Parent = parentCategorie
            };
            return _repo.CreateBegrotingsCategorie(begrotingsCategorie);
        }

Answer 1

I think your ICollection<BegrotingsCategorie> children property is giving you noise in your BegrotingsCategorie class. There is a one or zero-to-one recursive relationship of BegrotingsCategorie s defined somewhere in your code. However, you are trying to use a one-to-many relationship of BegrotingsCategorie s in your class by declaring your property children as an ICollection . You may want to get rid of your children property in your BegrotingsCategorie class if you really do not need it. This may be a possible workaround.