Entity Framework n to n relationship add object to another object-CodePudding

I have a Model with Clients:

public class Client

{
    [Key]
    public int id { get; set; }
    [Required]
    public string? Hostname { get; set; }
    public ICollection<Software>? Softwares { get; set; }

}

And a Model with Software:

public class Software
    {
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int id { get; set; }
        public string Name { get; set; }
        public ICollection<Client>? Clients { get; set; }
    }

This is supposed to be an n to n connection. How can I add software to my clients?

What I've tried:

public async void add(Software software)
        {
            using (var repo = new ClientRepository(contextFactory.CreateDbContext()))
            {
                client.Softwares.Add(software);
                await repo.Save(client);
            }

Repository:

public async Task Save(Client client)
        {
            _context.Clients.Update(client);
            _context.SaveChanges();
        }
        }

This works for the first software I add, but gives me the following error if I try to add a second one:

SqlException: Violation of PRIMARY KEY constraint 'PK_ClientSoftware'. Cannot insert duplicate key in object 'dbo.ClientSoftware'. The duplicate key value is (7003, 5002).

CodePudding user response：

Q: Do you make a new one with new() every time?

A: no, its a software that already exists

Then that is the error.
The first SaveChanges() will start tracking it as Existing. You can check: The Id will be != 0.

When you then later add it to the same Client you'll get the duplicate error.

So somewher in your code:

  await add(software);       // existing
  software = new Software(); // add this

Related, change:

public async void add(Software software)

public async Task Add(Software software)

Always avoid async void.

CodePudding user response：

It seems you are adding more than one relation of the same. Before adding software to a client, make sure a relation does not exist yet, then you can go ahead and add software to client.

Also, you can improve your entities. Use better naming for the primary keys and add [Key] attribute to Software class as well.

Client:

public class Client
{
    public Client()
    {
        Softwares = new HashSet<Software>();
    }

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ClientId { get; set; }
    [Required]
    public string Hostname { get; set; }
    public ICollection<Software> Softwares { get; set; }
}

Software:

public class Software
{
    public Software()
    {
        Clients = new HashSet<Client>();
    }
    
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int SoftwareId { get; set; }
    public string Name { get; set; }
    public ICollection<Client> Clients { get; set; }
}

Check if relation already exists:

// Get the client including its related softwares
var client = dbContext.Clients.Include(x => x.Softwares)
    .FirstOrDefault(x => x.Hostname == "Ibrahim");


if (client != null)
{
    // Check with unique property such as name of software
    // If it does not exist in this current client, then add software
    if (!client.Softwares.Any(x => x.Name == software.Name))
        client.Softwares.Add(software);

    dbContext.SaveChanges();
}

Note: If you update your entities, remember to create new migration and database.