LINQ EF7 ASP.NET and many-to-many - asp.net-mvc

Question

How i could add records to my database , with relation many-to-many in ASP.NET MVC 6 ?
I tried like that, but it's wrong
[HttpPost]
public IActionResult addpersons(Person pers)
{
var ourdoc = db.Documents.FirstOrDefault(p => p.Documentid == docselected);
ourdoc.DocPers.Add(ourdoc);
db.SaveChanges();
return Content("s");
}
Listings of my model files :
DocContext.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.Data.Entity;
namespace TDS_1_ASPNETMVC6.Models
{
public class DocPer
{
public int Documentid { get; set; }
public Document Document { get; set; }
public int Personid { get; set; }
public Person Person { get; set; }
}
public class DocContext : DbContext
{
public virtual DbSet<Document> Documents { get; set; }
public virtual DbSet<Person> Persons { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<DocPer>()
.HasKey(t => new
{
t.Documentid,
t.Personid
});
modelBuilder.Entity<DocPer>()
.HasOne(pt => pt.Document)
.WithMany(p => p.DocPers)
.HasForeignKey(pt => pt.Documentid);
modelBuilder.Entity<DocPer>()
.HasOne(pt => pt.Person)
.WithMany(t => t.DocPers)
.HasForeignKey(pt => pt.Personid);
}
}
}
Documents.cs
using System.Collections.Generic;
namespace TDS_1_ASPNETMVC6.Models
{
public class Document
{
public int Documentid { get; set; }
public string Name { get; set; }
public string Props { get; set; }
public List<DocPer> DocPers { get; set; }
}
}
Person.cs
using System.Collections.Generic;
namespace TDS_1_ASPNETMVC6.Models
{
public class Person
{
public int Personid { get; set; }
public string Iname { get; set; }
public string Fname { get; set; }
public string Oname { get; set; }
public string Email { get; set; }
public List<DocPer> DocPers { get; set; }
}
}

Answer 1

First, your controller is not checking for null; what if var ourdoc = db.Documents.FirstOrDefault(p => p.Documentid == docselected); is null? So check for null first :)
Also ourdoc.DocPers.Add(ourdoc); must be changed to ourdoc.DocPers.Add(new DocPer {Person = person});
Second, to create a many-to-many I suggest you to remove the DocPer table and map it "behind", like this:
public class Document
{
public Document()
{
Persons = new List<Person>();
}
public int Documentid { get; set; }
public string Name { get; set; }
public string Props { get; set; }
public virtual ICollection<Person> Persons { get; set; }
}
public class Person
{
public Person()
{
Documents = new List<Document>();
}
public int Personid { get; set; }
public string Iname { get; set; }
public string Fname { get; set; }
public string Oname { get; set; }
public string Email { get; set; }
public virtual ICollection<Document> Documents { get; set; }
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Document>()
.HasMany<Person>(s => s.Persons)
.WithMany(c => c.Documents)
.Map(cs =>
{
cs.MapLeftKey("Documentid");
cs.MapRightKey("Personid");
cs.ToTable("DocPer");
});
}
DocPer table will be managed by the EF without exposing it. Check this site for more details. This guide will apply to EF6 only, not EF7 (which does not support many-to-many yet, for that support check this link). BTW, EF7 is still is not stable yet, so is possibile that this support will be offered in the future, but no one knows yet.