Question

I am just learning Linq and ran into a problem. For some validation, I am getting the last odometer reading from our database and need to compare that to the next reading. The odometer reading is an int on the incoming data and double on the database (changed to int on the dbml file).

Below is my code:

private bool IsValidOdometer(string equipment, int odometerReading)
{
    bool returnVariable = true;
    CarteGraphDataDataContext db = new CarteGraphDataDataContext();

    var odometer = (from p in db.EquipmentMainGenerals join q in db.EquipmentFuelLogs 
            on p.wdEquipmentMainGeneralOID equals q.wdEquipmentMainGeneralOID
            where p.VehicleId == equipment
            orderby q.Odometer descending
            select q.Odometer).Take(1);

    int previousOdometer = odometer;

    if (odometer.Count() != 0)
    {
        if (odometerReading < previousOdometer)
        {
            returnVariable = false;
        }
    }

    return returnVariable;
}

The problem line is int previousOdometer = odometer;. The error I get is:

Cannot implicitly convert type ‘System.Linq.IQueryable’ to ‘int’

How do I fix this?

Answer 1

Instead of Enumerable.Take use Enumerable.Single. Enumerable.Take will return an IEnumerable but Enumerable.Single will return a single instance (or throw):

int odometer = (from p in db.EquipmentMainGenerals
                join q in db.EquipmentFuelLogs 
                on p.wdEquipmentMainGeneralOID
                    equals q.wdEquipmentMainGeneralOID
                where p.VehicleId == equipment
                orderby q.Odometer descending
                select q.Odometer).Single();

int previousOdometer = odometer;

Also, I would explicitly type odometer here instead of implicitly as you’ve done.

Lastly your line

CarteGraphDataDataContext db = new CarteGraphDataDataContext();

should really be in using block like so

using(CarteGraphDataDataContext db = new CarteGraphDataDataContext()) {
    // okay to go
}