Register one to many relationship in ASP.NET MVC - asp.net

Question

I have two classes - parent and child.
This is the parent class
[Table("tbl_Parent")]
public partial class Parent
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
[Key]
[ScaffoldColumn(false)]
public int Parent_Id { get; set; }
[Required(ErrorMessage = "you must provide parent First Name")]
[Display(Name = "Full Name")]
public string Parent_Full_Name{ get; set; }
[Required(ErrorMessage = "you must provide parent Email Address")]
[Display(Name = "Email Address")]
[DataType(DataType.EmailAddress)]
[EmailAddress(ErrorMessage = "Correct Input")]
[StringLength(100, ErrorMessage = "at least 10 Char", MinimumLength = 10)]
public string Parent_Email { get; set; }
[Required(ErrorMessage = "you must provide parent phone number")]
[Display(Name = "Phone Number")]
[DataType(DataType.PhoneNumber)]
public int Parent_Phone { get; set; }
[Required(ErrorMessage = "you must provide parent password")]
[Display(Name = "Password")]
[DataType(DataType.Password)]
public string Parent_Password { get; set; }
public string Parent_Location { get; set; }
[Required(ErrorMessage = "you must provide parent status")]
[Display(Name = "Parent status")]
public string Parent_status { get; set; }
public string Par_User_Type { get; set; }
public ICollection<Child> child { get; set; }
}
and this is the child class
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int Chi_Id { get; set; }
[Required(ErrorMessage ="you must provide child first name")]
[Display(Name ="Child First Name")]
public string Chi_First_Name { get; set; }
[Required(ErrorMessage ="you must provide child last Name")]
[Display(Name ="Child Last Name")]
public string Chi_Last_Name { get; set; }
[Required(ErrorMessage ="you must provide child age")]
[Display(Name ="Child Age")]
[Range(0,18, ErrorMessage = "Correct Input")]
public int Age { get; set; }
[Required(ErrorMessage ="you must provide child gender")]
[Display(Name ="Child Gender")]
public string Gender { get; set; }
[Display(Name ="Child School")]
public string Chi_School { get; set; }
[Required(ErrorMessage ="you must provide parent status")]
[Display(Name ="Child Parent Status")]
public string Chi_parent_status { get; set; }
[Display(Name ="Child Image Path")]
public string Chi_Image_Path { get; set; }
public virtual Admin admin { get; set; }
public int Adm_ID { get; set; }
public virtual Parent parent { get; set; }
public int Par_ID { get; set; }
}
The parent class can have many children.
I want add id of child in parent class across controller. This is my controller:
[HttpGet]
public ActionResult Rigester()
{
if (Session["ID"] == null)
{
return RedirectToAction("Login", "Home");
}
return View();
}
[HttpPost]
public ActionResult Rigester(Parent parent,int id)
{
if (ModelState.IsValid)
{
using (Context db = new Context())
{
var child1 = db.child.Where(x => x.Chi_Id == id).First();
parent.Par_User_Type = "Parent";
parent.child.Add(child1);
db.parent.Add(parent);
db.SaveChanges();
return RedirectToAction("Home", "Admin");
}
}
return View();
}
In the controller, I get an error when executing this code:
Null reference exception
on this line of code:
parent.child.Add(child1);
The end of each class has relationship between another class.
How can I add child when register new parent?

Answer 1

Instead of adding via navigation properties, in your controller you could assign the ParentId as foreign key for the child.
In the code below, first we added parent to the database, then we assigned the parentId in the child object.
[HttpPost]
public ActionResult Rigester(Parent parent,int id)
{
if (ModelState.IsValid)
{
using (Context db = new Context())
{
parent.Par_User_Type = "Parent";
db.parent.Add(parent);
db.SaveChanges();
var child1 = db.child.Where(x => x.Chi_Id == id).First();
child1.Par_Id = parent.Parent_Id;
db.SaveChanges();
return RedirectToAction("Home", "Admin");
}
}
return View();
}