没有EF对象的C＃EF6多对多插入

Question

public class MyContext : DbContext
{
    public DbSet<Foo> Foos {get;set;}
    public DbSet<Bar> Bars {get;set;}
    //some model creation about many to many (i ommitted it for simplicity)
}

public class Foo
{
    public long Id {get;set;}
    public virtual ICollection<Bar> Bars {get;set;}
}

public class Bar
{
    public long Id {get;set;}
    public virtual ICollection<Foo> Foos {get;set;}
}

这将创建3个表：Foos，Bars，FooBars（关系表）

那么，只有一个类型为Foo的对象和Bar id的列表，如何在不首先通过EF6中的选择查询请求整个对象的情况下将这些多对多id插入关系表中？

var barIds = new List<long>(){ /*...*/};
var foo = ctx.Foos.Single(x=> x.Id == 666);
foo.Bars = ctx.Bars.Select(x=> barIds.Contains(x.Id)).ToList();//this is hilarious query and very inefficient