c# - 保存父项时嵌套的现有实体重复

Question

我在尝试保存嵌套了现有实体的新实体时遇到问题。它不是与现有实体建立关系，而是复制它们。

这大概是我的模型:

public class Record
{
    public int ID { get; set; }
    public string RecordValue { get; set; }
    public virtual ICollection<AddressLine> AddressLines { get; set; }
}
public class AddressLine
{
    public int ID { get; set; }
    public string AddressLineValue { get; set; }
    public virtual ICollection<AddressLineType> AddressLineTypes { get; set; }
}
public class AddressLineType
{
    public int ID { get; set; }
    public string AddressLineTypeValue { get; set; }
}

我不想添加任何重复的 AddressLineTypes，所以在我的代码中我正在做这样的事情:

public void button1_Click(object sender, EventArgs e)
{

    Record r = new Record();
    r.RecordValue = "Record value";

    AddressLine al = new AddressLine();
    al.AddressLineValue = "Address line value";

    AddressLineType alt;
    using (var db = new MyDbContext())
    {
        alt = db.AddressLineTypes.Single(x => x.Value == "TypeValue");
    }

    al.AddressLineTypes.Add(alt);
    r.AddressLines.Add(al);

    SaveRecord(r);
}

public void SaveRecord(Record r)
{
    using (var db = new MyDbContext())
    {
        db.Records.Add(r);
        db.SaveChanges();
    }
}

我在 db.SaveChanges() 和 AddressLineType ID 之前遇到了断点，但它在数据库中创建了新条目，就好像 ID == 0。

如何在保存时停止复制现有的 AddressLineTypes？

Answer 1

尝试使用单个上下文:

...    
using (var db = new MyDbContext())
        {
            alt = db.AddressLineTypes.Single(x => x.Value == "TypeValue");


            al.AddressLineTypes.Add(alt);
            r.AddressLines.Add(al);

            SaveRecord(r, db);
        }
    }

public void SaveRecord(Record r, MyDbContext db)
{
        db.Records.Add(r);
        db.SaveChanges();
}