c# - 在 ASP.NET MVC 中传递匿名类型

Question

我在 C# 中使用 ASP.net MVC。为什么这是代码:

public IQueryable<Product> ListProducts(string prodcutType)
{
    var results = from p in db.Products
        join s in db.Stocks
        on p.ID equals s.IDProduct
        where p.ptype == prodcutType
        select new { s.width, s.height, s.number};                 
    return results;
}

显示以下错误？

Error 1 Cannot implicitly convert type System.Linq.IQueryable<AnonymousType#1> to System.Linq.IQueryable<eim.Models.Product>. An explicit conversion exists (are you missing a cast?)

Answer 1

因为 select new { s.width, s.height, s.number}表示 System.Linq.IQueryable<AnonymousType#1>但是你的函数期望返回 IQueryable<Product> .将您的代码更改为:

public IQueryable<Product> ListProducts(string prodcutType)
{

    var results = from p in db.Products
                  join s in db.Stocks
                  on p.ID equals s.IDProduct
                  where p.ptype == prodcutType
                  select p;
    return results;
}

更新:

或者您可能需要 IQueryable<Stock> :

public IQueryable<Stock> ListProducts(string prodcutType)
{

    var results = from p in db.Products
                  join s in db.Stocks
                  on p.ID equals s.IDProduct
                  where p.ptype == prodcutType
                  select s;
    return results;
}

如果你只想要 3 个属性 width+height+number 创建新类型。例如:

public class SomeType {
    public int Width { get; set; }
    public int Height { get; set; }
    public int Number { get; set; }
}

public IQueryable<SomeType> ListProducts(string prodcutType)
{

    var results = from p in db.Products
                  join s in db.Stocks
                  on p.ID equals s.IDProduct
                  where p.ptype == prodcutType
                  select new SomeType {
                      Width = s.width,
                      Height = s.height,
                      Number = s.number
                  };
    return results;
}