Linq to SQL How to write "not-in" query - entity-framework

Question

I have the following 3 tables ( 1 base table and other 2 sattelite tables for each vehicle type.)
Vehicles
ID VehicleType
-----------------------------
1 Car
2 Truck
Cars
ID Make Model
-------------------------
1 Toyota Camry
2 Honda Accord
Trucks
ID Make Model
--------------------
1 Ford F150
2 Dodge Ram
Then i have corresponding DTO
public class VehicleDTO
{
public int ID {get;set;}
public int VehicleType {get;set;}
public IEnumerable<CarDTO> Cars {get;set;}
public IEnumerable<TruckDTO> Trucks {get;set;}
}
public class CarDTO
{
public int ID {get;set;}
public string Make {get;set;}
public string Model {get;set;}
}
public class TruckDTO
{
public int ID {get;set;}
public string Make {get;set;}
public string Model {get;set;}
}
Then i have list of Vehicle DTO as an argument to the method. I want find vehicles from DTO list that does not exists in the database by matching Make and Model for that Vehicle Type.
Idea is to then insert the missing vehicles into database.
I have the following query
public void FindMissingVehicles(IEnumerable<VehicleDTO> dtos)
{
var cars = (from dto in dtos
where !(from c in dbcontext.Cars
select new { c.Make, c.Model })
.Any(x => dto.VehicleType == 'Car' && dto.Car.Make == x.Make && dto.Car.Model == x.Model)
select dto).ToList();
var trucs = (from dto in dtos
where !(from t in dbcontext.Trucks
select new { t.Make, t.Model })
.Any(x => dto.VehicleType == 'Truck' && dto.Truck.Make == x.Make && dto.Truck.Model == x.Model)
select dto).ToList();
//insert missing cars and trucks into db here
}
The query above throws exception
Message "Non-static method requires a target." string
Questions
1> How do i construct this query.
2> Can i make this query async by using AnyAsync and ToListAsync. (I know i have to make method async with Task, and use await inside howevere i could not figure out the async query syntax)

Answer 1

Moreover, your approach has performance issue - you perform N queries - one for each of dto, instead of doing only two queries: one for cars and one for trucks:
var allCars = dtos.Where(x => x.VehicleType == "Car").ToList()
.SelectMany(x => x.Cars.Select(y => y.Make + "-" + y.Model).ToList()).ToList();
var existedCars = await dbcontext.Cars.Where(x => allCars.Contains(x.Make + "-" + x.Model))
.Select(x => x.Make + "-" + x.Model).ToListAsync();
var newCars = allCars.Except(existedCars).Select(x =>
{
var temp = x.Split('-');
return new CarDTO
{
Make = temp[0],
Model = temp[1]
};
}).ToList();
//exactly same code for Trucks

Answer 2

This is because of you can't have nested query in linq when one table is from dbContext and the other one is from in-memory enumerable, so if dbcontext.Cars and dbcontext.Trucks don't have a lot of rows, it's a good idea to load them in memory and use nested query like below:
var listCars = dbcontext.Cars.ToList();
var listTrucks = dbcontext.Trucks.ToList();
var cars = (from dto in dtos
where !(from c in listCars
select new { c.Make, c.Model })
.Any(x => dto.VehicleType == 'Car' && dto.Car.Make == x.Make && dto.Car.Model == x.Model)
select dto).ToList();
var trucs = (from dto in dtos
where !(from t in listTrucks
select new { t.Make, t.Model })
.Any(x => dto.VehicleType == 'Truck' && dto.Truck.Make == x.Make && dto.Truck.Model == x.Model)
select dto).ToList();