[英]how to write this LINQ query of 3 tables?
表1 CAR(CARID,CarModelID,CARuniqueinfo1,CARUniqueinfo2):表示已将所有汽车输入仓库。
表2 CarModel(CarModelID,Modelinfo1,Modelinfo2)
表3销售(SaleID,CarID,clientID,EmpID)
返回的Linq查询是什么:
仅ModelID = 101的售出汽车数量
DataClassesDataContext db = new DataClassesDataContext();
简单方法:
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)
};
假设您有一个用于Sale(CarID)
的导航属性:
int all = db.Models
.Where(m => m.Cars.SelectMany(c => c.Sales).Any())
.Select(m => new {m.ModelID, m.Cars.Count}).ToArray();
var counts = Model.GroupBy(m => m.CarModelID)
.Select(grp => ModelId = grp.Key, Count = grp.Count())
这个:
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());
}
将为您提供一本词典,该词典将汽车ID映射到已售出的金额。
carsSold[1]
将返回ID为1的汽车的销售金额。
private int GetCarsSoldCount(int modelId)
{
return db.Sale.Count(x => x.CarID == modelId);
}
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() };
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