Question

你能告诉我Linq2SQL对我的sql server执行查询的位置吗？我希望在映射到名为Car的域名对象后发生这种情况。

public class Car
{
    public Guid CarId { get; set; }
    public string Make { get; set; }
    public string Model { get; set; }
    public int HorsePower { get; set; }
}

public class CarRepository
{
    private readonly MyDataContext _dc;

    private readonly Func<DbCar, Car> _mappedCar =
        c => new Car
                 {
                     CarId = c.CarId,
                     HorsePower = c.HorsePower,
                     Make = c.Make,
                     Model = c.Model,
                 };

    public CarRepository(MyDataContext dc)
    {
        _dc = dc;
    }

    public Car GetCar(Guid carId)
    {
        var car = _dc.GetTable<DbCar>()
            .Select(_mappedCar)
            .Single(c => c.CarId == carId);                

        return car;
    }        
}

Answer 1

这是对的。延迟执行SQL查询，直到调用Single()为止。您可以通过像这样断开查询并添加断点来确认这一点：

var carQuery = _dc.GetTable<DbCar>().Select(_mappedCar)  // <= breakpoint
var car = carQuery.Single(c => c.CarId == carId);

如果对数据库运行profiler，则应该在逐步执行代码时看到执行查询的位置。

此处有更多信息：LINQ and Deferred Execution

Linq-to-SQL何时运行查询？

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