[英]Entity Framework select object based on filters accross multiple child collections
假设我拥有以下域(不是我的实际域,而是一个简单的示例)
public class ClassRoom
{
public int Id {get;set;}
public string Name {get;set;}
public virtual ICollection<Desk> Desks{get;set;}
public virtual ICollection<LunchBox> LunchBoxs{get;set;}
}
public class Desk
{
public int Id {get;set;}
public String Colour {get;set;}
public String Make {get;set;}
Public ClassRoom ClassRoom {get;set;}
}
public class LunchBox
{
public int Id {get;set;}
public String Colour {get;set;}
public int Volume {get;set;}
}
我希望能够如下查询
“给我所有有蓝色书桌或绿色午餐盒的课程”,返回课程列表
我本以为代码是
var efClasses = (from d in myentity.ClassRooms
where ( (d.Desks.Colour == "blue")
|| (d.LunchBoxs.Colour == "green) )
select d).Distinct();
这样做给我错误
无法将lambda表达式转换为“字符串”类型,因为它不是委托类型(显然对颜色不满意,它期望在此处使用一种方法
所以我把它改成了实验
var efClasses = (from d in myentity.ClassRoom
where ( (d.Desks.Where(x=>x.Colour == "blue"))
|| (d.LunchBoxs.Where(x=>x.Colour == "green)) )
select d).Distinct();
但这也不会编译(事后看来,我有一种运气。
我可以通过将my更改为myentity.Desks和myEntity.Lunchboxs,然后返回两个单独的ClassRooms列表,然后找到并集,来进行另一种方法,但这将需要2次单独的数据库命中,并且感觉很hack
代替使用count> 0,可以使用Any
var efClasses = (from d in myentity.ClassRoom
where (d.Desks.Any(x => x.Colour == "blue") ||
d.LunchBoxs.Any(x => x.Colour == "green"))
select d);
像这样使用Count> 0。
var efClasses = (from d in myentity.ClassRoom
where (d.Desks.Count(x => x.Colour == "blue") > 0
|| d.LunchBoxs.Count(x => x.Colour == "green") > 0)
select d);
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