Multiple request instead of one in EF Core - .net-core

Question

I have this select which I expected to be executed by sending one command to SQL Server but I can see 10s requests instead. How can I fix it?
We have Companies which have Customers and Orders. For some reasons Orders are under Company entity.
var q = _dbContext.Companies
.Include(x => x.Customers)
.Include(c => c.Orders)
.Where(a => a.CompanyId == 123);
var total = await q.CountAsync();
q = q.OrderByDescending(x => x.CompanyCode)
.Skip((pageIndex - 1) * pageSize).Take(pageSize);
var res = await q.Select(x => new ResultDto()
{
CompanyCode = x.CompanyCode,
Customers = x.Customers
.Where(c => c.IsActive)
.Select(c => new CustomerDto()
{
FirstName = c.FirstName,
Surname = c.Surname,
Orders = x.Orders
.Where(o => o.IsOpen)
.Select(o => new OrderDto()
{
DateCreated = o.DateCreated
}).ToList()
}).FirstOrDefault(),
}).ToListAsync();

Answer 1

This is EF.NetCore optimization.
You actually cant achieve one query when your navigation properties are collections.
I can't find any links right now, but this is by design.
Once you have a collection in your navigations inside select or inside includes it will produce a separate query for each root entity. The reason I believe is the redundant data amount produced by such a query.
I suggest leave it as is if you have not a lot of data < 1000 rows in a result. You will see a lot of queries but they will be really fast.
As I can see you have pagination here so it shouldn't be a problem.
Otherwise, select your collections separately and join them in memory carefully.
Unfortunately, there is no other way for EF Core
Also, I recommend to turn on EF core logs to what is going on early. I bet FirstOrDefault will produce some warning.