iot/labs/EFCoreTest/Program.cs

using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;

namespace EFCoreTest
{
    public class MyDbContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlite("Data Source=data.db;");
            //optionsBuilder.UseMySql("Server=139.180.143.95;Port=3306;Database=test;Uid=admin;Pwd=admin;");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<User>();
            modelBuilder.Entity<Role>();
            modelBuilder.Entity<UserRole>().HasOne(o => o.User).WithMany(o => o.UserRoles).HasForeignKey(o => o.UserId);
            modelBuilder.Entity<UserRole>().HasOne(o => o.Role).WithMany(o => o.UserRoles).HasForeignKey(o => o.RoleId);
            modelBuilder.Entity<UserRole>().HasIndex(o => new { o.UserId, o.RoleId }).IsUnique();
        }
    }

    public class Entity
    {
        public Guid Id { get; set; }

        public Entity()
        {
            this.Id = Guid.NewGuid();
        }
    }

    public class User : Entity
    {
        public string UserName { get; set; }
        public List<UserRole> UserRoles { get; set; } = new List<UserRole>();
    }

    public class Role : Entity
    {
        public string Name { get; set; }
        public List<UserRole> UserRoles { get; set; } = new List<UserRole>();
    }

    public class UserRole : Entity
    {
        public Guid UserId { get; set; }
        public Guid RoleId { get; set; }
        public User User { get; set; }
        public Role Role { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            using (var db = new MyDbContext())
            {
                if (db.Database.EnsureCreated())
                {
                    db.Set<User>().Add(new User { UserName = "test" });
                    db.SaveChanges();
                }
                Console.WriteLine(db.Set<User>().FirstOrDefault()?.UserName);
            }
        }
    }
}