如何编写3表的LINQ查询？

Question

• Table1 CAR (CARID, CarModelID ,CARuniqueinfo1, CARUniqueinfo2): contians all cars have been entered to the warehouse.

• Table2 CarModel (CarModelID ,Modelinfo1 ,Modelinfo2 )

• Table3 Sale (SaleID, CarID, clientID, EmpID)

What is the Linq Query that returns :

number of sold cars only for ModelID=101

DataClassesDataContext db = new DataClassesDataContext(); 

Answer 1

Simple Way:

var result =
    db.Sale
        .GroupBy(item => item.CarId)
        .Select(item => new { item.Key, item.Count() });

Nice way:

var result =
    from sale in db.Sale

    join car in db.CAR
    on car.CARID equals sale.CarID

    join carModel in db.CarModel
    on carModel.CarModelID equals car.CarModelID

    select new 
    { 
        Model = carModel,
        SoldCars = db.Sale.Count(item => item.CarID == car.CARID)
    };

Answer 2

Assuming you have a navigation propertiy for Sale(CarID) :

int all = db.Models
            .Where(m => m.Cars.SelectMany(c => c.Sales).Any())
            .Select(m => new {m.ModelID, m.Cars.Count}).ToArray();

Answer 3

var counts = Model.GroupBy(m => m.CarModelID)
                  .Select(grp => ModelId = grp.Key, Count = grp.Count())

Answer 4

This:

Dictionary<int, int> carsSold = new Dictionary<int, int>();
foreach (Car in Cars) {
 carrsold.Add(x => x.Id, Sales.Where(y => y.CarId == x.Id).Count());
}

will leave you with a dictionary that maps car id to amount sold.

carsSold[1] would return amount sold by the car with id of 1.

Answer 5

private int GetCarsSoldCount(int modelId)
{
  return db.Sale.Count(x => x.CarID == modelId);
}

Answer 6

        var r = from car in CarTable
                from sale in SalesTable
                where sale.CarID == car.CarID
                group sale by car.CarModelID into g
                select new { Model = g.Key, Count = g.Count() };