如何从多对多关系数据库中返回对象 - entityframework

Question

Im trying to return a List of products of a specific user by user Id, but that seems to not work

My Product class

public class Product
{
    [Key]
    public int Id { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public decimal Price { get; set; }
    public int Quantity { get; set; }
    
    public List<User>? Users { get; set; }
}

My user class

public class User
{
    [Key]
    public Guid Id { get; set; }
    
    [Required] [MaxLength(15)]
    public string Username { get; set; }
    
    [Required]
    public string Name { get; set; }
    public string Surname { get; set; }
    public string PasswordHash { get; set; }
    public string Salt { get; set; }

    public List<Product>? Products { get; set; }
}

So im adding and Product to Db, this is working

And then im adding the product to Order by this method Guid id is a user's id

    public void AddProduct(Product product, Guid id)
    {
        var user = _context.Users.First(u => u.Id == id);

        var p = _context.Products.First(p => p.Id == product.Id);

        if (user.Products == null || p.Users == null)
        {
            user.Products = new List<Product>();
            p.Users = new List<User>();
        }
        
        user.Products.Add(p);
        p.Users.Add(user);
        
        _context.SaveChanges();
    }

And this also seems to work: image of ProductUser table from db

So how can I return a List of Products which specific user have?

I've tried this:

    private Order BuildOrder(Guid id)
    {
        var user = _context.Users.First(u => u.Id == id);

        /*if (user.Products is null)
        {
            user.Products = new List<Product>();
        }*/

        var x = _context.Products.Where(p => p.Id == 1);
        
        /*
        var products = user.Products.ToList();*/
        
        var order = new Order
        {
            Products = x.ToList()
        };

        return order;

But this is returning me null, like Adding Products is not working Result of this method

Order class:

public class Order
{
    public List<Product> Products { get; set; }
}

DbContext:

using Application.Api.Models;
using Microsoft.EntityFrameworkCore;

namespace Application.Api.Data;

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

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.UseSerialColumns();

        modelBuilder.Entity<User>(eb =>
        {
            eb.HasMany(u => u.Products).WithMany(p => p.Users);
        });

    }

    public DbSet<User> Users { get; set; }
    public DbSet<Product> Products { get; set; }
}

If that's not enough informations comment what I need to add

Answer 1

您需要为用户明确包含产品

var speceficUserWithProducts = context.Users.Include(u => u.Products).FirstOrDefault(u => u.Id == id);