我已经看过这个话题BETWEEN EQUIVALENT in LINQ
我在SQL中的原始查询:
SELECT ISNULL(Tcar.name, '') FROM dbo.models model
LEFT JOIN cars Tcar on Tcar.model = model.id AND
Tcar.year between model.Start and model.End
我需要在“左连接”内部之间实现,我试过这个:
我的课程:
public class car
{
public string name { get; set; }
public int model { get; set; }
public DateTime year { get; set; }
}
public class model
{
public int id { get; set; }
public DateTime Start { get; set; }
public DateTime End { get; set; }
}
我的实施:
var theModel = from model in models
join Tcar in cars
on new
{
ID = (int)model.id,
DateStart = (DateTime)model.Start,
DateEnd = (DateTime)model.End
}
equals new
{
ID = (int)Tcar.model,
DateStart = (DateTime)Tcar.year,
DateEnd = (DateTime)Tcar.year
} into tempCar
from finalCar in tempCar
select new
{
CAR = (finalCar == null ? String.Empty : finalCar.name)
};
解决方法:
var theModel = from model in models
join Tcar in cars
on model.id equals Tcar.model
where model.Start <= Tcar.year && model.End >= Tcar.year
select new
{
CAR = Tcar.name
};
如果我使用解决方法Linq翻译为此查询:
SELECT Tcar.name FROM dbo.models model
LEFT JOIN cars Tcar on Tcar.model == model.id
WHERE model.Start <= Tcar.year and model.End >= Tcar.year
我可以在“select new”之前放一个简单的地方,但是我必须通过这种方式实现,在左边的join中有“between”,我该怎么做?
答案 0 :(得分:5)
编辑 - 添加DefaultOrEmpty()
以使其成为左连接
像这样修改你的查询,这将强制where子句进入join on子句。它不会在Join中给你Between子句,但至少不会有where子句
var theModel = from model in models
from Tcar in cars.Where(x => model.id == x.model)
.Where(x => model.Start <= x.year && model.End >= x.year)
.DefaultOrEmpty()
select new
{
CAR = Tcar.name
};
答案 1 :(得分:2)
SQL Server应该考虑您的原始查询和LINQ生成的示例是相同的,因为WHERE model.Start <= Tcar.year and model.End >= Tcar.year
和ON Tcar.year between model.Start and model.End
都指定了连接条件。
通常首选使用ON
,因为它会使您的加入条件与其他搜索条件分开,但这是为了提高可读性而非性能。在我躺着的几张桌子上测试类似的查询会产生相同的查询计划,如果您看到不同的桌面计划,我会感到惊讶。