C# 使用具有fluent api的复合外键配置一对零或一关系

我正在用EntityFramework6.1.0开发一个C.NETFramework4.0

我有一个现有的数据库，并用它生成了代码类

这些是我的课程：

[Table("CODES")]
public partial class CODE
{
    public CODE()
    {
    }

    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long ID_CODE { get; set; }

    [Key]
    [Column(Order = 0)]
    public byte CODE_LEVEL { get; set; }

    [Key]
    [Column("CODE", Order = 1)]
    [StringLength(20)]
    public string CODE1 { get; set; }

    public byte? COMMISIONING_FLAG { get; set; }

    public bool? IS_TRANSMITTED { get; set; }

    public DateTime? TIMESPAN { get; set; }

    [StringLength(50)]
    public string USERNAME { get; set; }

    [StringLength(50)]
    public string SOURCE { get; set; }

    public virtual AGGREGATION_CHILDS AGGREGATION_CHILDS { get; set; }

    public virtual AGGREGATION AGGREGATIONS { get; set; }
}

public partial class AGGREGATION_CHILDS
{
    [Key]
    [Column(Order = 0)]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public long ID_AGGREGATION { get; set; }

    [Key]
    [Column(Order = 1)]
    [StringLength(20)]
    public string ID_CHILD { get; set; }

    [Key]
    [Column(Order = 2)]
    public byte CODE_LEVEL { get; set; }

    public int POSITION { get; set; }

    public virtual AGGREGATION AGGREGATION { get; set; }

    public virtual CODE CODE { get; set; }
}

[Table("AGGREGATIONS")]
public partial class AGGREGATION
{
    public AGGREGATION()
    {
        AGGREGATION_CHILDS = new HashSet<AGGREGATION_CHILDS>();
    }

    [Key]
    public long ID_AGGREGATION { get; set; }

    [StringLength(20)]
    public string ID_PARENT { get; set; }

    public byte? PARENT_LEVEL { get; set; }

    public virtual ICollection<AGGREGATION_CHILDS> AGGREGATION_CHILDS { get; set; }

    public virtual CODE CODE { get; set; }
}

以及代码和聚合之间的另一种一对一关系

但在聚合中，外键是可选的：ID\u PARENT和PARENT\u LEVEL可以为NULL

如何在OnModelCreating上设置这两种关系

public partial class MyDbContext : DbContext
{
    public MyDbContext()
        : base("name=MyDbContext")
    {
    }

    public virtual DbSet<AGGREGATION_CHILDS> AGGREGATION_CHILDS { get; set; }
    public virtual DbSet<AGGREGATION> AGGREGATIONS { get; set; }
    public virtual DbSet<CODE> CODES { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<AGGREGATION>()
            .HasMany(e => e.AGGREGATION_CHILDS)
            .WithRequired(e => e.AGGREGATION)
            .WillCascadeOnDelete(false);
    }
}

CODES.CODE1      -> AGGREGATION_CHILDS.ID_CHILD
CODES.CODE_LEVEL -> AGGREGATION_CHILDS.CODE_LEVEL

CODES.CODE1      -> AGGREGATION.ID_PARENT
CODES.CODE_LEVEL -> AGGREGATION.PARENT_LEVEL