有一种名为Product的实体类型是由实体框架生成的。
我写了这个问题
public IQueryable<Product> GetProducts(int categoryID)
{
return from p in db.Products
where p.CategoryID== categoryID
select new Product { Name = p.Name};
}
下面的代码抛出以下错误:
实体或复杂类型的Shop。产品不能构造在
LINQ到实体查询"
var products = productRepository.GetProducts(1).Tolist();
但是当我使用select p而不是select new Product {Name = p.Name};它工作正常。
如何执行自定义选择节?
为了回应另一个被标记为重复的问题(见这里),我根据Soren的答案想出了一个快速而简单的解决方案:
data.Tasks.AddRange(
data.Task.AsEnumerable().Select(t => new Task{
creator_id = t.ID,
start_date = t.Incident.DateOpened,
end_date = t.Incident.DateCLosed,
product_code = t.Incident.ProductCode
// so on...
})
);
data.SaveChanges();
注意:
这个解决方案只适用于Task类上有一个导航属性(外键)(这里称为“Incident”)。
如果你没有,你可以使用“AsQueryable()”其他发布的解决方案之一。
它不会让您映射回Product,因为这是您正在查询的表。你需要一个匿名函数,然后你可以将它添加到一个ViewModel,并将每个ViewModel添加到List<MyViewModel>并返回这些。这是一个轻微的题外话,但我包含了关于处理可为空日期的警告,因为这是一个难以处理的问题,以防您有任何问题。我是这样处理的。
希望你有一个ProductViewModel:
public class ProductViewModel
{
[Key]
public string ID { get; set; }
public string Name { get; set; }
}
我有依赖注入/存储库框架,我调用一个函数来获取我的数据。以你的帖子为例,在你的Controller函数调用中,它看起来是这样的:
int categoryID = 1;
var prods = repository.GetProducts(categoryID);
在存储库类中:
public IEnumerable<ProductViewModel> GetProducts(int categoryID)
{
List<ProductViewModel> lstPVM = new List<ProductViewModel>();
var anonymousObjResult = from p in db.Products
where p.CategoryID == categoryID
select new
{
CatID = p.CategoryID,
Name = p.Name
};
// NOTE: If you have any dates that are nullable and null, you'll need to
// take care of that: ClosedDate = (DateTime?)p.ClosedDate ?? DateTime.Now
// If you want a particular date, you have to define a DateTime variable,
// assign your value to it, then replace DateTime.Now with that variable. You
// cannot call a DateTime.Parse there, unfortunately.
// Using
// new Date("1","1","1800");
// works, though. (I add a particular date so I can edit it out later.)
// I do this foreach below so I can return a List<ProductViewModel>.
// You could do: return anonymousObjResult.ToList(); here
// but it's not as clean and is an anonymous type instead of defined
// by a ViewModel where you can control the individual field types
foreach (var a in anonymousObjResult)
{
ProductViewModel pvm = new ProductViewModel();
pvm.ID = a.CatID;
pvm.Name = a.Name;
lstPVM.Add(rvm);
}
// Obviously you will just have ONE item there, but I built it
// like this so you could bring back the whole table, if you wanted
// to remove your Where clause, above.
return lstPVM;
}
回到控制器,你需要:
List<ProductViewModel> lstProd = new List<ProductViewModel>();
if (prods != null)
{
// For setting the dates back to nulls, I'm looking for this value:
// DateTime stdDate = DateTime.Parse("01/01/1800");
foreach (var a in prods)
{
ProductViewModel o_prod = new ReportViewModel();
o_prod.ID = a.ID;
o_prod.Name = a.Name;
// o_prod.ClosedDate = a.ClosedDate == stdDate ? null : a.ClosedDate;
lstProd.Add(o_prod);
}
}
return View(lstProd); // use this in your View as: @model IEnumerable<ProductViewModel>