如何自动添加一对多对象

Question

我是ASP.NET MVC的新手，我在尝试插入对象时遇到问题1xn自动使用我的方法Create。我想知道如何插入对象RelUserHomes，我需要homeId，但它只存在于db.SaveChanges（）之后。

这是一个片段：

Controller Homes

[HttpPost]    
[ValidateAntiForgeryToken]    
public ActionResult Create([Bind(Include = "HomeId,Name")] Home home)    
{    
    if (ModelState.IsValid)
     {    
         db.Homes.Add(home);    
         RelUserHomes relUserHomes = new RelUserHomes();  

        // I did this because I need the homeId to insert this object    
         relUserHomes.HomeId = db.SaveChanges();    
         relUserHomes.Email = Session["Email"].ToString();
         relUserHomes.IsAdmin = true;
         db.RelUserHomes.Add(relUserHomes);    
         db.SaveChanges();    
    }
    return View(home);
}

Model RelUserHomes

public class RelUserHomes
{
    [Key]
    public int RelUserHomesId { get; set; }

    public bool IsAdmin { get; set; }

    [Required]
    public string Email { get; set; }

    [Required]
    public int HomeId { get; set; }
    [Key]
    public Home Homes { get; set; }
}

Application DBContext

public class ApplicationDbContext : IdentityDbContext<ApplicationUser> 
{
    public ApplicationDbContext() : base("PrimoEntities")
    {
    }

    public override int SaveChanges()
    {
        try
        {
            return base.SaveChanges();
        }
        catch (DbEntityValidationException ex)
        {
           // Retrieve the error messages as a list of strings.
            var errorMessages = ex.EntityValidationErrors.SelectMany(x => x.ValidationErrors).Select(x => x.ErrorMessage);
            var fullErrorMessage = string.Join("; ", errorMessages);
            var exceptionMessage = string.Concat(ex.Message, " The validation errors are: ", fullErrorMessage);
            // Throw a new DbEntityValidationException with the improved exception message.
            throw new DbEntityValidationException(exceptionMessage, ex.EntityValidationErrors);
        }
     }

     public DbSet<Home> Homes { get; set; }

     public DbSet<RelUserHomes> RelUserHomes { get; set; }
}

Answer 1

如果RelUserHomes实体具有指向Home实体的外键关系，则必须首先将Home对象添加到数据库，以便为其分配{{1价值。您只需在代码中稍早添加HomeId，然后分配db.SaveChanges() relUserHomes HomeId属性Home.

尝试将代码更改为以下内容：

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create([Bind(Include = "HomeId,Name")] Home home)
{
    if (ModelState.IsValid)
     {
         db.Homes.Add(home);
         db.SaveChanges();
         RelUserHomes relUserHomes = new RelUserHomes();

         relUserHomes.HomeId = home.HomeId;
         db.RelUserHomes.Add(relUserHomes);
         db.SaveChanges();

    }
    return View(home);
}