所以这是我的问题...我试图创建的是一种自我参照的多对多关系。基本上这是我的模型。
val four = Succ (Succ (Succ (Succ Zero)))
这个想法是系统可以有很多父母,而一个父母可以有很多孩子。我知道如何创建一个自引用实体,其中许多孩子可以有一个父母。使我绊倒的是很多部分。下面是我的DbContext。
public class InformationSystem
{
public InformationSystem()
{
Systems = new HashSet<InformationSystem>();
ParentSystems = new HashSet<InformationSystem>();
}
[Key()]
public int InformationSystemID { get; set; }
public string InformationSystemName { get; set; }
//Navigation properties
public virtual ICollection<InformationSystem> Systems { get; set; }
public virtual ICollection<InformationSystem> ParentSystems { get; set; }
}
但是,在我的DbContext上,我收到一个错误:.WithMany不包含许多将接受类型集合输入的定义。我知道,当代码首次创建迁移并更新数据库时,基本上需要构建的是链接表。我认为链接表将具有两列且没有键。一栏为InformationSystemID,一栏为ParentInformationSystemID。两者都是外键。我也知道,要使其正常工作,应该限制删除行为,以便在链接表中删除或更新条目时,该更改不会级联(并创建循环)。有人可以指出正确的方向以使EF Core 3正确执行此操作吗?如果必须自己创建一个链接表,我该怎么做?在DbContext中我需要做什么?我知道链接表看起来像这样:
我将不胜感激。
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<InformationSystem>(entity =>
{
entity
.HasMany(e => e.ParentSystems)
.WithMany(e => e.Systems)
.OnDelete(DeleteBehavior.Restrict);
});
答案 0 :(得分:1)
在EF Core中,必须在模型中包含一个实体以 代表M:N关系中的联接表,然后向其中一个添加导航属性 指向联接实体的多对多关系的另一端。
新表格S:
public class InformationSystem
{
public InformationSystem()
{
}
[Key()]
public virtual int InformationSystemID { get; set; }
public virtual string InformationSystemName { get; set; }
public virtual ICollection<InformationSystemRelation> Systems { get; set; }
public virtual ICollection<InformationSystemRelation> ParentSystems { get; set; }
}
public class InformationSystemRelation
{
public int ParentId { get; set; }
public InformationSystem Parent { get; set; }
public int ChildId { get; set; }
public InformationSystem Child { get; set; }
}
映射:
modelBuilder.Entity<InformationSystemRelation>()
.HasKey(x => new { x.ParentId, x.ChildId });
modelBuilder.Entity<InformationSystemRelation>()
.HasOne(x => x.Parent)
.WithMany(x => x.Systems)
.HasForeignKey(x => x.ParentId)
.OnDelete(DeleteBehavior.Restrict);
modelBuilder.Entity<InformationSystemRelation>()
.HasOne(x => x.Child)
.WithMany(x => x.ParentSystems)
.HasForeignKey(x => x.ChildId)
.OnDelete(DeleteBehavior.Restrict);
整个样本:
class Program
{
static void Main(string[] args)
{
var db = new MyDbContext();
var is1 = new InformationSystem() { InformationSystemName = "is1" };
var is2 = new InformationSystem() { InformationSystemName = "is2" };
var is3 = new InformationSystem() { InformationSystemName = "is3" };
var is4 = new InformationSystem() { InformationSystemName = "is4" };
db.InformationSystems.Add(is1);
db.InformationSystems.Add(is2);
db.InformationSystems.Add(is3);
db.InformationSystems.Add(is4);
db.SaveChanges();
var r1 = new InformationSystemRelation() { ParentId = 1, ChildId = 2 };
var r2 = new InformationSystemRelation() { ParentId = 1, ChildId = 3 };
var r3 = new InformationSystemRelation() { ParentId = 4, ChildId = 2 };
var r4 = new InformationSystemRelation() { ParentId = 2, ChildId = 3 };
var r5 = new InformationSystemRelation() { ParentId = 2, ChildId = 4 };
db.InformationSystemRelations.Add(r1);
db.InformationSystemRelations.Add(r2);
db.InformationSystemRelations.Add(r3);
db.InformationSystemRelations.Add(r4);
db.InformationSystemRelations.Add(r5);
db.SaveChanges();
var o2 = db.InformationSystems.Include(x => x.Systems).Include(x => x.ParentSystems).Single(x => x.InformationSystemID == 2);
}
}
public class InformationSystem
{
public InformationSystem()
{
}
[Key()]
public virtual int InformationSystemID { get; set; }
public virtual string InformationSystemName { get; set; }
public virtual ICollection<InformationSystemRelation> Systems { get; set; }
public virtual ICollection<InformationSystemRelation> ParentSystems { get; set; }
}
public class MyDbContext : DbContext
{
public DbSet<InformationSystem> InformationSystems { get; set; }
public DbSet<InformationSystemRelation> InformationSystemRelations { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<InformationSystem>(entity =>
{
modelBuilder.Entity<InformationSystemRelation>()
.HasKey(x => new { x.ParentId, x.ChildId });
modelBuilder.Entity<InformationSystemRelation>()
.HasOne(x => x.Parent)
.WithMany(x => x.Systems)
.HasForeignKey(x => x.ParentId)
.OnDelete(DeleteBehavior.Restrict);
modelBuilder.Entity<InformationSystemRelation>()
.HasOne(x => x.Child)
.WithMany(x => x.ParentSystems)
.HasForeignKey(x => x.ChildId)
.OnDelete(DeleteBehavior.Restrict);
});
}
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseSqlServer("data source=(local)\\SQLEXPRESS;Initial catalog=Test;Integrated security=SSPI");
base.OnConfiguring(optionsBuilder);
}
}
public class InformationSystemRelation
{
public int ParentId { get; set; }
public InformationSystem Parent { get; set; }
public int ChildId { get; set; }
public InformationSystem Child { get; set; }
}