无法在 LINQ to Entities 查询中构造实体 [英] The entity cannot be constructed in a LINQ to Entities query

问题描述

有一个实体类型叫做Product，它是由实体框架生成的.我写了这个查询

There is an entity type called Product that is generated by entity framework. I have written this query

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

下面的代码抛出以下错误:

The code below throws the following error :

"实体或复杂类型 Shop.Product 不能在LINQ to Entities 查询"

"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 select p 而不是 select new Product { Name = p.Name}; 时，它可以正常工作.

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

如何执行自定义选择部分?

How can I preform a custom select section?

推荐答案

您不能(也不应该能够)投影到映射实体上.但是，您可以投影到匿名类型或 DTO:

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

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

你的方法将返回一个 DTO 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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