Entity framework 插入/更新多个对象

我有以下课程：

public class Location
{
    public int Id { get; set; }
    public string Description { get; set; }
    public string CarId { get; set; } 
    public Car Car { get; set; }
}

public class Car
{
    public string Id { get; set; }
    public string Color { get; set; } 
}

还有一个观点：

    <div>@Html.LabelFor(location => location.Description)</div>
    <div>@Html.EditorFor(location => location.Description)</div>

    <div>@Html.LabelFor(location => location.Car.Id)</div>
    <div>@Html.EditorFor(location => location.Car.Id)</div>

    <div>@Html.LabelFor(location => location.Car.Color)</div>
    <div>@Html.EditorFor(location => location.Car.Color)</div>

它在“db.SaveChanges”中中断，因为它说“无法在对象“dbo.Car”中插入重复的密钥”

如果删除“db.Location.Add（locacao）；”，因此，它对汽车（插入和更新）的效果非常好，但数据库中没有添加任何位置

---

如何在数据库中没有汽车id时插入新车，在有id时更新，并插入新位置？

Add

方法始终添加对象图中的所有实体，以便

db.car.Add（location.car）

和

db.location.Add（location）

都插入位置和汽车

试试这个：

db.Location.Add(locacation);
// You can also use another way to find if you are working with a new Car 
// like location.Car.Id == 0
if (db.Car.Any(c => c.Id == location.Car.Id)) 
{
    db.Entry(location.Car).State = EntityState.Modified;
}
db.SaveChanges();  

db.Location.Add(locacation);
// You can also use another way to find if you are working with a new Car 
// like location.Car.Id == 0
if (db.Car.Any(c => c.Id == location.Car.Id)) 
{
    db.Entry(location.Car).State = EntityState.Modified;
}
db.SaveChanges();