Linq - Order by in Include

Question

I have a situation where OrderBy need to be done for Include object. This is how I have tried so far

Customers query = null;

try
{
    query = _context.Customers
        .Include(x => x.CustomerStatus)
        .ThenInclude(x => x.StatusNavigation)
        .Select(x => new Customers()
        {
            Id = x.Id,
            Address = x.Address,
            Contact = x.Contact,
            Name = x.Name,
            CustomerStatus = new List<CustomerStatus>
            {
                x.CustomerStatus.OrderByDescending(y => y.Date).FirstOrDefault()
            }
        })
        .FirstOrDefault(x => x.Id == 3);
}
catch (Exception ex)
{
    throw;
}

The above code successfully ordering the include element but it is not including it's child table. Eg: Customer include CustomerStatus but CustomerStatus not including StatusNavigation tables.

I even tried with this but neither it can help me

_context.Customers
    .Include(x => x.CustomerStatus.OrderByDescending(y => y.Date).FirstOrDefault())
    .ThenInclude(x => x.StatusNavigation).FirstOrDefault(x => x.Id == 3);

What am I doing wrong please guide me someone

Even I tried this way

var query = _context.CustomerStatus
    .GroupBy(x => x.CustomerId)
    .Select(x => x.OrderByDescending(y => y.Date).FirstOrDefault())
    .Include(x => x.StatusNavigation)
    .Join(_context.Customers, first => first.CustomerId, second => second.Id, (first, second) => new Customers
    {
        Id = second.Id,
        Name = second.Name,
        Address = second.Address,
        Contact = second.Contact,
        CustomerStatus = new List<CustomerStatus> {
            new CustomerStatus
            {
                Id = first.Id,
                CustomerId = first.CustomerId,
                Date = first.Date,
                StatusNavigation = first.StatusNavigation
            }
        },
    }).FirstOrDefault(x => x.Id == 3);

but this is hitting a databases a 3 times and filtering the result in memory. First select all data from customer status and then from status and then from customer then it filter all the data in memory. Is there any other efficient way to do this??

This is how I have prepared by entity class

Answer 1

As @Chris Pratt mentioned once you are doing new Customer inside the select you are creating a new model. You are discarding the models build by the EntityFramework. My suggestion would be have the query just:

query = _context.Customers
    .Include(x => x.CustomerStatus)
    .ThenInclude(x => x.StatusNavigation);

Like this you would have an IQueryable object which it would not be executed unless you do a select from it:

var customer3 = query.FirstOrDefault(x=>x.Id==3)

Which returns the customer and the interlinked tables (CustomerStatus and StatusNavigation). Then you can create the object that you want:

var customer = new Customers()
    {
        Id = customer3.Id,
        Address = customer3.Address,
        Contact = customer3.Contact,
        Name = x.Name,
        CustomerStatus = new List<CustomerStatus>
        {
            customer3.CustomerStatus.OrderByDescending(y => y.Date).FirstOrDefault()
        }
    })

In this way you can reuse the query for creating different response objects and have a single querying to database, but downside is that more memory is used then the original query (even though it shouldn't be too much of an issue).

If the model that is originally return from database doesn't meet the requirements (i.e. you always need to do: CustomerStatus = new List {...} ) it might indicate that the database schema is not well defined to the needs of the application, so a refactoring might be needed.

Answer 2

After Reading from Couple of sources (Source 1) and (Source 2). I think what is happening is that If you use select after Include. It disregards Include even if you are using Include query data in select. So to solve this use .AsEnumerable() before calling select.

query = _context.Customers
    .Include(x => x.CustomerStatus)
    .ThenInclude(x => x.StatusNavigation)
    .AsEnumerable()
    .Select(x => new Customers()
    {
        Id = x.Id,
        Address = x.Address,
        Contact = x.Contact,
        Name = x.Name,
        CustomerStatus = new List<CustomerStatus>
        {
            x.CustomerStatus.OrderByDescending(y => y.Date).FirstOrDefault()
        }
    })
    .FirstOrDefault(x => x.Id == 3);

Answer 3

What I think is happening is that you are actually overriding the Include and ThenInclude. Include is explicitly to eager-load a navigation property. However, you're doing a couple of things that are likely hindering this.

First, you're selecting into a new Customer. That alone may be enough to break the logic of Include. Second, you're overriding what gets put in the CustomerStatus collection. That should ideally be just loaded in automatically via Include, but by altering it to just have the first entity, you're essentially throwing away the effect of Include. (Selecting a relationship is enough to cause a join to be issued, without explicitly calling Include). Third, the ThenInclude is predicated on the Include, so overriding that is probably throwing out the ThenIncude as well.

All this is conjecture. I haven't done anything exactly like what you're doing here before, but nothing else makes sense.

Try selecting into a new CustomerStatus as well:

CustomerStatus = x.CustomerStatus.OrderByDescending(o => o.Date).Select(s => new CustomerStatus
{
    x.Id,
    x.Status,
    x.Date,
    x.CustomerId,
    x.Customer,
    x.StatusNavigation
 })

You can remove the Include/ThenInclude at that point, because the act of selecting these relationships will cause the join.