实体框架多对象关系

Question

I have a table with 2 foreignkeys to the same parent table, Edge.StartStationId and Edge.EndStationId.

I am trying to map theese to objets in entity framework, but can't find a workaround which seems to fix the problem. I've found some solutions using 2 collections on the parent (Station), which I'm not interested in.

Station (parent) class:

public partial class Station
{
    public Station()
    {
        this.Reservations = new List<Reservation>();
        this.StationMaintenances = new List<StationMaintenance>();
    }

    public int ID { get; set; } 
    public int TypeId { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
    public decimal StationLat { get; set; }
    public decimal StationLong { get; set; }
    public bool IsOperational { get; set; }
    public bool IsActive { get; set; }
    public DateTime CreatedDate { get; set; }
    public virtual BatteryStorage BatteryStorages { get; set; }
    public virtual List<Reservation> Reservations { get; set; }
    public virtual List<StationMaintenance> StationMaintenances { get; set; }
    public virtual List<Edge> Edges { get; set; }
    public virtual StationType StationType { get; set; }
}

Edge (child) class:

public partial class Edge
{
    public int ID { get; set; }
    public int StartStationId { get; set; }
    public virtual Station StartStation { get; set; }
    public int EndStationId { get; set; }
    public virtual Station EndStation { get; set; }
    public decimal Distance { get; set; }
    public decimal Time { get; set; }
    public bool IsActive { get; set; }
}

The edge map class, which is added in OnModelCreating.

public EdgeMap()
{
    // Primary Key
    this.HasKey(t => t.ID);

    // Properties
    // Table & Column Mappings
    this.ToTable("Edges");
    this.Property(t => t.ID).HasColumnName("ID");
    this.Property(t => t.StartStationId).HasColumnName("StartStationId");
    this.Property(t => t.EndStationId).HasColumnName("EndStationId");
    this.Property(t => t.Distance).HasColumnName("Distance");
    this.Property(t => t.Time).HasColumnName("Time");
    this.Property(t => t.IsActive).HasColumnName("IsActive");

    // Relationships
    //this.HasOptional(t => t.StartStation)
    //    .WithMany(t => t.Edges)
    //    .HasForeignKey(d => d.StarStationId);
    //this.HasOptional(t => t.EndStation)
    //    .WithMany(t => t.Edges)
    //    .HasForeignKey(d => d.EndStationId);
}

Exception:

One or more validation errors were detected during model generation: System.Data.Entity.Edm.EdmAssociationType: : Multiplicity conflicts with the referential constraint in Role 'Edge_EndStation_Target' in relationship 'Edge_EndStation'. Because all of the properties in the Dependent Role are non-nullable, multiplicity of the Principal Role must be '1'.

Answer 1

I think the particular error you posted is complaining about the HasOptional . Since the foreign keys ( StartStationId and EndStationId ) are non-nullable, it's expecting a required mapping. Try changing it to HasRequired , or change the type of StartStationId and EndStationId to int? so that it knows the navigation properties can be null.

As for the Edges collection, what should it contain? Any Edge that references the Station with either the StartStationId or EndStationId values? If so, I don't think you can do that with a single collection.