实体不能在一个LINQ被构造为实体的查询 [英] The entity cannot be constructed in a LINQ to Entities query

问题描述

有是受实体框架生成称为产品的实体类型。
我已经writen此查询

There is an entity type called product that is generated by entity framework. I have writen this query

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

下code引发以下错误：实体或复杂类型Shop.Product不能在LINQ建造成Entities查询

The code below throws the following error : "The entity or complex type Shop.Product cannot be constructed in a LINQ to Entities query"

var products = productRepository.GetProducts(1).Tolist();

但是当我使用选择P 而不是选择新的产品名称{= p.Name}; 它的工作原理正确的。

But when I use select p instead of select new Product { Name = p.Name}; it works correctly.

我如何preform自定义选择部分？

How can I preform a custom select section?

推荐答案

您不能（也不应该能）项目拖到映射实体。你可以，但是，项目到一个annonymous类型或到 DTO ：

You cannot (and should not be able to) project onto a mapped entity. You can, however, project onto an annonymous type or onto a DTO:

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

和你的方法将返回DTO的一个列表。

And your method will return a List of DTO's.

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

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