实体框架插入FK

Question

I have the following classes:

public class User
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int UserId { get; set; }        
    public string Email { get; set; }
    [Required]
    public virtual Role Role { get; set; }
}


public class Role
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int RoleId { get; set; }
    [Required]
    public string RoleName { get; set; }        
}

I would like to insert a new User:

var user = new User()
{
   Email = "jhon@gmail.com",                    
   Role = ?
 };


 db.Users.Add(user);
 db.SaveChanges();

How do I insert the RoleId=1 as an FK ?

Answer 1

One thing I noticed is that the User Class is missing the RoleId navigation property.

If you don't mind adding navigation property to your User class, you can make below changes to achieve it.

    public class User
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int UserId { get; set; }        
        public string Email { get; set; }
        public int RoleId {get;set;}
        [Required]
        public virtual Role Role { get; set; }
    }

And now you can insert the User like this:

var user = new User()
{
   Email = "jhon@gmail.com",                    
   RoleId = db.Roles.Single(r => r.RoleName = "Role_Name").Select(x=>x.RoleId)
 };

db.Users.Add(user);
db.SaveChanges();

Answer 2

If it is a new role you would create special new role for that user like:

var role = new Role{
  RoleName = "Whatever"
} 

var user = new User(){
  Email = "jhon@gmail.com",
  Role = role
}
db.Users.Add(user);
db.SaveChanges();

If it is existing role and as you don't have navigation property would be best to fetch role from db to have db entity:

var role = db.Roles.Single(x => x.RoleName == "Whatever");
var user =  new User(){
   Email = "jhon@gmail.com",
   Role = role
 }
db.Users.Add(user);
db.SaveChanges();

Answer 3

The Identity option specifies that the value will only be generated by the database when a value is first added to the database. Thereafter, the property will not be included in UPDATE statements by Entity Framework.

To conclude, you don't need to set RoleId , just create object with RoleName and add it to database.