什么是EntityReference？

Question

如果我想绑定两个实体框架对象person1，person2与父子关系.比方说，对象来自不同的ObjectContexts或一个是分离的。好吧，现在，我想写这样的东西：

person1.Parent = person2;

这在SaveChanges()上失败了。所以我写：

person1.ParentReference.EntityKey = person2.EntityKey;

对于这个问题，这是一个正确的解决方案吗?还是应该总是重新加载“坏”对象(对象当前位于另一个ObjectContext中)？

Answer 1

给你一个直接的回答

想象一下你的桌子

[Tbl_Persons]

PersonId   int [PK]
ParentId   int [FK]
FirstName  nvarchar(100)
LastName   nvarchar(100)
CreateUser int
CreateDate datetime
UpdateUser int
UpdateDate datetime

您将有两个选项来分配一个父级

person1.Tbl_Persons = person2;

其中person1和person2都是TblPersons对象，或者简单地分配Id

person1.ParentId = person2.PersonId;

现在是一个完整的代码，这是我通常对数据库中的插入/更新所做的操作

public class MyRepository : IMyRepository
{
    MyEntities db = new MyEntities();
    DateTime now = DateTime.UTCNow;

    public void Save() {
        db.SaveChanges();
    }

    #region Update / Insert Persons

    public void UpdatePerson(Tbl_Persons person, int parentId, int userId)
    {
        // let's check if record is in db
        Tbl_Persons p = this.GetPersonById(person.PersonId); 
        if(p == null)
            p = new Person(); // person was not found in db

        p.FirstName = person.FirstName;
        p.LastName = person.LastName;

        // we can now hook up the parent object in 2 ways
        // or set the Id, or attach the hole object
        // NOTE: only choose one line!
        p.MyParent = parentId;
        p.TblParent = this.GetPersonById(parentId);

        // update info
        p.UpdateDate = now;
        p.UpdateUser = userId;


        if(p.PersonId == 0)
        {
            // is it new person in db, so we need to INSERT into the db
            p.CreateDate = now;
            p.CreateUser = userId;

            db.Tbl_Persons.AddObject(p);
        }
        else
        {
            // It's an existing person, we do need need to do anything
            // as internally once we assign a new value to the object that
            // come back from the database, EF sets Modified flag on this
        }

        // let's save
        this.Save();
    }

    #endregion

    #region Queries

        public Tbl_Persons GetPersonById(int personId)
        { 
            return db.Tbl_Persons.FirstOrDefault(x => x.PersonId == personId);
        }

    #endregion

}

在您的控制器中

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(Tbl_Persons model, int parentId)
{
    if(ModelState.IsValid)
    {
        db.UpdatePerson(model, parentId, currentUserId);
    }

    return RedirectToAction("Index");
}

希望能帮上忙。