C# 如何首先使用EF核心代码在表本身上桥接

这是我过去使用数据库优先的方法做过多次的操作。我现在先用EF-Core来尝试代码，结果失败得很惨

我有以下型号：

public class DataMapping
{
    [Key]
    [Column(Order = 1)]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long Id { get; set; }

    public string Model { get; set; } 
    public string Property { get; set; }
    public bool IgnoreProperty { get; set; } 

    [NotMapped] //<-- I had to add this as the migration was complaining that it did not know what the relation was
    public List<DataMappingRelation> DataMappingRelations { get; set; }

    public DateTime DateCreated { get; set; } = DateTime.UtcNow;
    public DateTime? DateModified { get; set; }
}

但是，此呼叫不起作用：

return _context.DataMappings.Where(x => x.Model == type.FullName)
            .Include(x=>x.DataMappingRelations)
            .ToList();

它不喜欢Include并抛出null ref异常

这里我基本上需要做的是，对于给定的“DataMapping”，根据“DataMappingRelations”表中的关系获取所有相关的DataMapping项

是的，我已经看过了，但再次强调，这是一个两个独立表的例子，而不是一个单独的表本身桥接

---

我怀疑我做错了这一切。我怎样才能让它工作？我发现的所有例子都是连接两个独立的表。这将桥接同一个表。

它的

多对多

与self，但您的整个配置看起来很混乱

因此，首先，您的

DataMapping

模型类应该包含

DataMappingRelation

中两个外键的两个列表导航属性，如下所示：

public class DataMapping
{
    ......

    public List<DataMappingRelation> DataMapping1Relations { get; set; }

    public List<DataMappingRelation> DataMapping2Relations { get; set; }

    .........
}

public class DataMappingRelation
{
    [Key]
    [Column(Order = 1)]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long Id { get; set; }

    public long? DataMapping1Id { get; set; }
    public DataMapping DataMapping1 { get; set; } 

    public long? DataMapping2Id { get; set; }
    public DataMapping DataMapping2 { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
     base.OnModelCreating(modelBuilder);

     modelBuilder.Entity<DataMappingRelation>()
         .HasOne(dmr => dmr.DataMapping1)
         .WithMany(dm => dm.DataMapping1Relations)
         .HasForeignKey(dmr => dmr.DataMapping1Id)
         .OnDelete(DeleteBehavior.Restrict);

     modelBuilder.Entity<DataMappingRelation>()
         .HasOne(dmr => dmr.DataMapping2)
         .WithMany(dm => dm.DataMapping2Relations)
         .HasForeignKey(dmr => dmr.DataMapping2Id)
         .OnDelete(DeleteBehavior.Restrict);
}

然后

Fluent API

配置应如下所示：

public class DataMapping
{
    ......

    public List<DataMappingRelation> DataMapping1Relations { get; set; }

    public List<DataMappingRelation> DataMapping2Relations { get; set; }

    .........
}

public class DataMappingRelation
{
    [Key]
    [Column(Order = 1)]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long Id { get; set; }

    public long? DataMapping1Id { get; set; }
    public DataMapping DataMapping1 { get; set; } 

    public long? DataMapping2Id { get; set; }
    public DataMapping DataMapping2 { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
     base.OnModelCreating(modelBuilder);

     modelBuilder.Entity<DataMappingRelation>()
         .HasOne(dmr => dmr.DataMapping1)
         .WithMany(dm => dm.DataMapping1Relations)
         .HasForeignKey(dmr => dmr.DataMapping1Id)
         .OnDelete(DeleteBehavior.Restrict);

     modelBuilder.Entity<DataMappingRelation>()
         .HasOne(dmr => dmr.DataMapping2)
         .WithMany(dm => dm.DataMapping2Relations)
         .HasForeignKey(dmr => dmr.DataMapping2Id)
         .OnDelete(DeleteBehavior.Restrict);
}

模型创建时受保护的覆盖无效（ModelBuilder ModelBuilder）
{
基于模型创建（modelBuilder）；
modelBuilder.Entity（）
.HasOne（dmr=>dmr.DataMapping1）
.WithMany（dm=>dm.DataMapping1关系）
.HasForeignKey（dmr=>dmr.DataMapping1Id）
.OnDelete（DeleteBehavior.Restrict）；
modelBuilder.Entity（）
.HasOne（dmr=>dmr.DataMapping2）
.WithMany（dm=>dm.DataMapping2关系）
.HasForeignKey（dmr=>dmr.DataMapping2Id）
.OnDelete（DeleteBehavior.Restrict）；
}