LINQ Practice

public class Dept
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int DeptId { get; set; }
}

public class Role
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class RoleUser
{
    public int RoleId { get; set; }
    public int UserId { get; set; }
}

public class Menu
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class RoleMenu
{
    public int RoleId { get; set; }
    public int MenuId { get; set; }
}

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

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

        modelBuilder.Entity<Dept>().ToTable("Dept").HasKey(v => v.Id);
        modelBuilder.Entity<Dept>().Property(v => v.Name).HasMaxLength(50).IsRequired(true);

        modelBuilder.Entity<User>().ToTable("User").HasKey(v => v.Id);
        modelBuilder.Entity<User>().Property(v => v.Name).HasMaxLength(50).IsRequired(true);
        modelBuilder.Entity<User>().Property(v => v.DeptId).IsRequired(true);

        modelBuilder.Entity<Role>().ToTable("Role").HasKey(v => v.Id);
        modelBuilder.Entity<Role>().Property(v => v.Name).HasMaxLength(50).IsRequired(true);

        modelBuilder.Entity<RoleUser>().ToTable("RoleUser").HasKey(v => new { v.RoleId, v.UserId });

        modelBuilder.Entity<Menu>().ToTable("Menu").HasKey(v => v.Id);
        modelBuilder.Entity<Menu>().Property(menu => menu.Name).HasMaxLength(50).IsRequired(true);

        modelBuilder.Entity<RoleMenu>().ToTable("RoleMenu").HasKey(v => new { v.RoleId, v.MenuId });
    }

    public DbSet<Dept> Depts { get; set; }
    public DbSet<User> Users { get; set; }
    public DbSet<Role> Roles { get; set; }
    public DbSet<RoleUser> RoleUsers { get; set; }
    public DbSet<Menu> Menus { get; set; }
    public DbSet<RoleMenu> RoleMenus { get; set; }
}

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<Database>(options =>
        {
            options.UseSqlServer(@"server=(localdb)\MSSQLLocalDb;database=LINQ;trusted_connection=true;");
        });
        services.AddMvc();
    }

    public void Configure(IApplicationBuilder app)
    {
        app.UseMvc();
    }
}

[Route("linq")]
public class LinqController : Controller
{
    private readonly Database _database;

    public LinqController(Database database)
    {
        _database = database;
    }

    [HttpGet]
    public IActionResult Get()
    {
        #region Depts
        var depts1 = from l in _database.Depts.AsNoTracking()
                        select new
                        {
                            l.Id,
                            l.Name,
                            Users = from r in _database.Users.AsNoTracking()
                                    where r.DeptId == l.Id
                                    select r
                        };

        var depts2 = _database.Depts.AsNoTracking()
            .Select(l => new
            {
                l.Id,
                l.Name,
                Users = _database.Users.AsNoTracking()
                    .Where(r => r.DeptId == l.Id)
                    .Select(r => r)
            });
        #endregion

        #region Users
        var rolesWithUserIds1 = from l in _database.RoleUsers.AsNoTracking()
                                join r in _database.Roles.AsNoTracking() on l.RoleId equals r.Id
                                select new
                                {
                                    l.RoleId,
                                    l.UserId,
                                    RoleName = r.Name // Role by UserId
                                };

        var usersWithRoleIds1 = from l in _database.RoleUsers.AsNoTracking()
                                join r in _database.Users.AsNoTracking() on l.UserId equals r.Id
                                select new
                                {
                                    l.RoleId,
                                    l.UserId,
                                    UserName = r.Name // User by RoleId
                                };

        var menusWithRoleIds1 = from l in _database.RoleMenus.AsNoTracking()
                                join r in _database.Menus.AsNoTracking() on l.MenuId equals r.Id
                                select new
                                {
                                    l.RoleId,
                                    l.MenuId,
                                    MenuName = r.Name // Menu by RoleId
                                };

        var menusWithUserIds1 = (from l in usersWithRoleIds1
                                    join r in menusWithRoleIds1 on l.RoleId equals r.RoleId
                                    select new
                                    {
                                        l.UserId,
                                        r.MenuId,
                                        r.MenuName // Menu by UserId
                                    }).Distinct();

        var users1 = from l in _database.Users.AsNoTracking()
                        join r in _database.Depts.AsNoTracking() on l.DeptId equals r.Id into lr // 左外连接
                        from r in lr.DefaultIfEmpty()
                        select new
                        {
                            l.Id,
                            l.Name,
                            DeptId = r == null ? 0 : r.Id,
                            DeptName = r == null ? null : r.Name,
                            Roles = from t in rolesWithUserIds1
                                    where t.UserId == l.Id
                                    select new
                                    {
                                        t.RoleId,
                                        t.RoleName
                                    },
                            Menus = from t in menusWithUserIds1
                                    where t.UserId == l.Id
                                    select new
                                    {
                                        t.MenuId,
                                        t.MenuName
                                    }
                        };

        var rolesWithUserIds2 = _database.RoleUsers.AsNoTracking()
            .Join(_database.Roles.AsNoTracking(), l => l.RoleId, r => r.Id, (l, r) => new
            {
                l.RoleId,
                l.UserId,
                RoleName = r.Name // Role by UserId
            });

        var usersWithRoleIds2 = _database.RoleUsers.AsNoTracking()
            .Join(_database.Users.AsNoTracking(), l => l.UserId, r => r.Id, (l, r) => new
            {
                l.RoleId,
                l.UserId,
                UserName = r.Name // User by RoleId
            });

        var menusWithRoleIds2 = _database.RoleMenus.AsNoTracking()
            .Join(_database.Menus.AsNoTracking(), l => l.MenuId, r => r.Id, (l, r) => new
            {
                l.RoleId,
                l.MenuId,
                MenuName = r.Name // Menu by RoleId
            });

        var menusWithUserIds2 = usersWithRoleIds2.Join(menusWithRoleIds2, l => l.RoleId, r => r.RoleId, (l, r) => new
        {
            l.UserId,
            r.MenuId,
            r.MenuName // Menu by UserId
        }).Distinct();

        var users2 = _database.Users.AsNoTracking()
            .GroupJoin(_database.Depts.AsNoTracking(), l => l.DeptId, r => r.Id, (l, rs) => new
            {
                User = l,
                Depts = rs
            })
            .SelectMany(lr => lr.Depts.DefaultIfEmpty(), (l, r) => new
            {
                l.User.Id,
                l.User.Name,
                DeptId = r == null ? 0 : r.Id,
                DeptName = r == null ? null : r.Name,
                Roles = rolesWithUserIds2.Where(t => t.UserId == l.User.Id),
                Menus = menusWithUserIds2.Where(t => t.UserId == l.User.Id)
            });
        #endregion

        #region Roles
        var roles1 = from l in _database.Roles.AsNoTracking()
                        select new
                        {
                            l.Id,
                            l.Name,
                            Menus = from t in menusWithRoleIds1
                                    where t.RoleId == l.Id
                                    select new
                                    {
                                        t.MenuId,
                                        t.MenuName
                                    }
                        };

        var roles2 = _database.Roles.AsNoTracking()
            .Select(l => new
            {
                l.Id,
                l.Name,
                Menus = menusWithRoleIds2.Where(t => t.RoleId == l.Id)
                .Select(t => new
                {
                    t.MenuId,
                    t.MenuName
                })
            });
        #endregion

        #region Menus
        var roleWithMenuIds1 = from l in _database.RoleMenus.AsNoTracking()
                                join r in _database.Roles.AsNoTracking() on l.RoleId equals r.Id
                                select new
                                {
                                    l.RoleId,
                                    l.MenuId,
                                    RoleName = r.Name  // Role by MenuId
                                };

        var menus1 = from l in _database.Menus.AsNoTracking()
                        select new
                        {
                            l.Id,
                            l.Name,
                            Roles = from t in roleWithMenuIds1
                                    where t.MenuId == l.Id
                                    select new
                                    {
                                        t.RoleId,
                                        t.RoleName
                                    }
                        };

        var roleWithMenuIds2 = _database.RoleMenus.AsNoTracking()
            .Join(_database.Roles.AsNoTracking(), l => l.RoleId, r => r.Id, (l, r) => new
            {
                l.RoleId,
                l.MenuId,
                RoleName = r.Name // Role by MenuId
            });

        var menus2 = _database.Menus.AsNoTracking()
            .Select(l => new
            {
                l.Id,
                l.Name,
                Menus = roleWithMenuIds2.Where(t => t.MenuId == l.Id)
                .Select(t => new
                {
                    t.RoleId,
                    t.RoleName
                })
            });
        #endregion

        return Ok(new { depts1, depts2, users1, users2, roles1, roles2, menus1, menus2 });
    }
}