这里有一种不声明额外类的方法:

public List<Product> GetProducts(int categoryID)
{
    var query = from p in db.Products
            where p.CategoryID == categoryID
            select new { Name = p.Name };
    var products = query.ToList().Select(r => new Product
    {
        Name = r.Name;
    }).ToList();

    return products;
}

但是，只有当您想将多个实体组合到一个实体中时，才可以使用这种方法。上面的功能(简单的产品到产品映射)是这样完成的:

public List<Product> GetProducts(int categoryID)
{
    var query = from p in db.Products
            where p.CategoryID == categoryID
            select p;
    var products = query.ToList();

    return products;
}

只添加AsEnumerable():

public IQueryable<Product> GetProducts(int categoryID)
{
    return from p in db.Products.AsEnumerable()
           where p.CategoryID== categoryID
           select new Product { Name = p.Name};
}

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>

如果你正在执行实体的Linq，你不能在查询的选择闭包中使用带有new的ClassType，只允许匿名类型(new没有类型)

看看我的项目的这个片段

//...
var dbQuery = context.Set<Letter>()
                .Include(letter => letter.LetterStatus)
                .Select(l => new {Title =l.Title,ID = l.ID, LastModificationDate = l.LastModificationDate, DateCreated = l.DateCreated,LetterStatus = new {ID = l.LetterStatusID.Value,NameInArabic = l.LetterStatus.NameInArabic,NameInEnglish = l.LetterStatus.NameInEnglish} })
                               ^^ without type__________________________________________________________________________________________________________^^ without type

如果你在选择闭包中添加了new关键字，即使在复杂的属性上，你也会得到这个错误

因此，从Linq上的new关键字删除类类型到实体查询，

因为它将转换为sql语句并在SqlServer上执行

什么时候我可以使用new with types on select closure?

如果你在处理LINQ to Object(内存收集)，你可以使用它

//opecations in tempList , LINQ to Entities; so we can not use class types in select only anonymous types are allowed
var tempList = dbQuery.Skip(10).Take(10).ToList();// this is list of <anonymous type> so we have to convert it so list of <letter>

//opecations in list , LINQ to Object; so we can use class types in select
list = tempList.Select(l => new Letter{ Title = l.Title, ID = l.ID, LastModificationDate = l.LastModificationDate, DateCreated = l.DateCreated, LetterStatus = new LetterStatus{ ID = l.LetterStatus.ID, NameInArabic = l.LetterStatus.NameInArabic, NameInEnglish = l.LetterStatus.NameInEnglish } }).ToList();
                                ^^^^^^ with type 

在我对查询执行了ToList后，它变成了内存集合，所以我们可以在选择中使用新的classttypes

你可以像下面这样添加AsEnumerable到你的集合:

public IQueryable<Product> GetProducts(int categoryID)
{
    return from p in db.Products.AsEnumerable()
           where p.CategoryID== categoryID
           select new Product { Name = p.Name};
}

您不能(也不应该)将项目投射到映射实体上。但是，你可以投射到匿名类型或DTO上:

public class ProductDTO
{
    public string Name { get; set; }
    // Other field you may need from the Product entity
}

您的方法将返回DTO的列表。

public List<ProductDTO> GetProducts(int categoryID)
{
    return (from p in db.Products
            where p.CategoryID == categoryID
            select new ProductDTO { Name = p.Name }).ToList();
}