Foreign key relation on WebAPI class

Question

--- Solution ---

Thanks all for helping me, I was doing 1 thing wrong, I had 2 contexts because I didn't understand the concept, but now I've fixed it.

Here's what I changed based on your comments for it to work:

public class DatabaseContext : DbContext
{
    public DatabaseContext(DbContextOptions<DatabaseContext> options)
        : base(options)
    {
    }

    public DbSet<Grupo> Grupos { get; set; }
    public DbSet<Produto> Produtos { get; set; }

}

public class ProdutoRepository : IDefaultRepository<Produto>
{
    private readonly DatabaseContext _context;

    public ProdutoRepository(DatabaseContext context)
    {
        _context = context;

        if (_context.Produtos.Count() == 0)
            Add(new Produto { Nome = "Teste", GrupoId = 1 });
    }

    public IEnumerable<Produto> GetAll()
    {
        return _context.Produtos.Include(p => p.Grupo).ToList();
    }

    public void Add(Produto item)
    {
        _context.Produtos.Add(item);
        _context.SaveChanges();
    }

    public Produto Find(long key)
    {
        return _context.Produtos.Include("Grupo").FirstOrDefault(t => t.Id == key);
    }

    public void Remove(long key)
    {
        var entity = _context.Produtos.First(t => t.Id == key);
        _context.Produtos.Remove(entity);
        _context.SaveChanges();
    }

    public void Update(Produto item)
    {
        _context.Produtos.Update(item);
        _context.SaveChanges();
    }
}

public class GrupoRepository : IDefaultRepository<Grupo>
{
    private readonly DatabaseContext _context;

    public GrupoRepository(DatabaseContext context)
    {
        _context = context;

        if (_context.Grupos.Count() == 0)
            Add(new Grupo { Nome = "Teste" });
    }

    public IEnumerable<Grupo> GetAll()
    {
        return _context.Grupos.ToList();
    }

    public void Add(Grupo item)
    {
        _context.Grupos.Add(item);
        _context.SaveChanges();
    }

    public Grupo Find(long key)
    {
        return _context.Grupos.FirstOrDefault(t => t.Id == key);
    }

    public void Remove(long key)
    {
        var entity = _context.Grupos.First(t => t.Id == key);
        _context.Grupos.Remove(entity);
        _context.SaveChanges();
    }

    public void Update(Grupo item)
    {
        _context.Grupos.Update(item);
        _context.SaveChanges();
    }
}

--- /Solution ---

--- EDIT #4 ---

I don't know if I should point that I want it to be automatic, if I put a FK, I want to point it to the object so it will bring it on the JSON without making it manually.

--- /EDIT #4 ---

--- EDIT #3 ---

Okay, so I couldn't solve it, so I put the code on GitHub so you could take a look, is just a test project so no problem, is a small project.

https://github.com/heronz/LysiSolutionNumber01

--- /EDIT #3 ---

I'm new to C# and WebAPI development and I'm trying to learn how to make the relationship of 2 objects using a foreign key and when to access the endpoint I'd like it to bring something like this:

{
    productId:1,
    productName:"Test",
    productGroupId:1
    productGroup:{
        groupId:1,
        groupName:"Test Group"
    }
}

But I'm getting something like this:

{
    productId:1,
    productName:"Test",
    productGroupId:1
    productGroup:null
}

In my classes, I'm already using the annotations like this

public class Product
{        
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long productId{ get; set; }
    public string productName{ get; set; }

    [ForeignKey("group")]
    public long productGroupId{ get; set; }        
    public virtual Group productGroup{ get; set; }
}

public class Group
{        
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long groupId{ get; set; }
    public string groupName{ get; set; }
}

And I'm using the repository/context as taught in this tutorial

https://learn.microsoft.com/en-us/aspnet/core/tutorials/first-web-api

When I initiate my repository I use it like this:

public ProductRepository(ProductContext context)
{
    _context = context;

    if (_context.Reg.Count() == 0)
        Add(new Product{ productName = "Test", productGroupId= 1 });
}

I've tried searching how should I do it, found something about DTO but I didn't understand, so maybe there's that.

I'm in the process of learning, so there's no ready application only something I build based on the tutorial that I mentioned above.

--- EDIT ---

As asked on the comments, here is the GET method.

public IEnumerable<Product> GetAll()
{
    return _context.Reg.ToList();
}

public Produto Find(long key)
{
    return _context.Reg.FirstOrDefault(t => t.Codigo == key);
}

This is the context (edited):

public class ProductContext : DbContext
{
    public ProductContext(DbContextOptions<ProductContext> options)
        : base(options)
    {
    }

    public DbSet<Product> Reg { get; set; }

}

--- EDIT #2 ---

Tried adding a products reference on group

public class Group
{        
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long groupId{ get; set; }
    public string groupName{ get; set; }
    public virtual ICollection<Product> Products{ get; set; }
} 

And on the GET methods added the included thing

public IEnumerable<Product> GetAll()
{
    return _context.Reg.Include(p => p.productGroup).ToList();
}

public Produto Find(long key)
{
    return _context.Reg.Include(p => p.productGroup).FirstOrDefault(t => t.Codigo == key);
}

Still not working, maybe there's something with the way I reference the group in here?

public ProductRepository(ProductContext context)
{
    _context = context;

    if (_context.Reg.Count() == 0)
        Add(new Product{ productName = "Test", productGroupId= 1 });
}

Because, this way I'm only referencing the FK, maybe I need to reference the object? But how?

Answer 1

You will need to make some changes:

---

ProductContext

Add the following line

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

---

Classe Product

Delete the following property

public long productGroupId { get; set; }

The system already recognizes FK and creates the field at the base.

---

Class where you insert the new product

Here, you will get the group from database (assuming the group is already registered)

var group = _context.Group.Find(1);

Create a new product collection if it is null.

if (group.Products == null)
    group.Products = new List<Product>();

And then you add to the list of products for the selected group.

 group.Products.Add(new Product { productName = "Test" });

---

Staying like this:

public ProductRepository(ProductContext context)
{
    _context = context;
    var group = _context.Group.Find(1);

    if (group.Products == null)
        group.Products = new List<Product>();

    if (_context.Reg.Count() == 0)
       group.Products.Add(new Product { productName = "Test" });
}