如何編寫3表的LINQ查詢？

Question

• 表1 CAR（CARID，CarModelID，CARuniqueinfo1，CARUniqueinfo2）：表示已將所有汽車輸入倉庫。

• 表2 CarModel（CarModelID，Modelinfo1，Modelinfo2）

• 表3銷售（SaleID，CarID，clientID，EmpID）

返回的Linq查詢是什么：

僅ModelID = 101的售出汽車數量

DataClassesDataContext db = new DataClassesDataContext(); 

Answer 1

簡單方法：

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

好方法：

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

假設您有一個用於Sale(CarID)的導航屬性：

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

這個：

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());
}

將為您提供一本詞典，該詞典將汽車ID映射到已售出的金額。

carsSold[1]將返回ID為1的汽車的銷售金額。

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() };