go-queryset | safe ORM for Go with code generation | SQL Database library

I am working to learn Django, and have built a test database to work with. I have a table that provides basic vendor invoice information, so, and I want to simply present a user with the total value of invoices that have been loaded to into the database. I found that the following queryset does sum the column as I'd hoped:

I'm using Django filters (django-filter) in my project. I have the models below, where a composition (Work) has a many-to-many instrumentations field with a through model. Each instrumentation has several instruments within it.

models.py:

Let's say I have a model My_model and I have a list of ids for this model;

I'm loosely following the example laid out here:

Django Queryset with filtering on reverse foreign key

Model:

I have two model like this with following fields:

I have a Django application with Django Rest Framework that is storing records in Postgres. A Vehicle model has an end_date DateField that represents the final payment date of a finance agreement, and a monthly_payment FloatField that represents the payment amount. The finance payment is made monthly, on the same day of the month as the final payment (e.g. if end_date is 25/01/2020, a payment is made on the 25th of every month between now and 25/01/2020 inclusive.)

I have a ListVehicle ListCreateAPIView that returns a paginated list of vehicle records. I am using a custom PageNumberPagination class to return a data object alongside the results array that is populated by aggregating some of the fields in the Vehicle model. I want to include a field in this data object that contains the total remaining amount left to pay on all of the Vehicle entities in the database.

I have tried using @property fields in the model that calculate the total remaining amount for each Vehicle, but you can't aggregate over calculated properties (at least not with queryset.aggregate), so the following solution did not work:

i am trying to make the following view with return JsonResponse() at the end work correctly:

In my views.py, I do:

I'm having doubt regarding lazy evaluation in django-querysets.

This is my django query:

Method1:

tyres_in_car = Car.objects.filter(serial_no__startswith('AB')).values('tyre__type')

In this query I'm accessing foreign key values using .values() (tyre type) in this case.

Another approach which I use is:

Method2:

Line1 : tyres = Car.objects.filter(serial_no__startswith('AB'))

Line2 : all_tyres = tyres.tyre.all()

Line3 : tyres_in_car = [ ty.type for ty in all_tyres ]

Since, I'm using .values() in both the methods, does the query hits database only once in both the cases( because of lazy evaluation in case of Method 2) or it hits two times in case of Method 2.

From the perspective of code readability, Method 2 looks more appropriate in my opinion.