如何在LINQ lambda扩展方法中插入方法 [英] How to insert a method inside a LINQ lambda extension method

问题描述

我必须在LINQ lambda内放置一个方法.我有以下代码:

I have to place a method inside a LINQ lambda. I have the following code:

string productName = "Some product";

searchShoppingCart = shoppingCart.Where(m => productName.Equals(_ProductRepository.GetProductName(m.Id)));

基本上，此代码用于选择所有包含productName的shoppingCart实例.

Basically this code is used to select all the shoppingCart instances that contain productName.

方法string GetProductName(int shoppingCartId)是_ProductRepository中的一种方法，它返回一个产品的名称.此方法的实现方式及其逻辑无关紧要.

The method string GetProductName(int shoppingCartId) is a method from _ProductRepository that returns the name of one product. How this method is implemented and its logic does not matter.

问题是LINQ抛出异常.我知道引发此异常的原因，我只想知道一种解决方法.我尝试过

The problem is that LINQ throws an exception. I know the reasons why this exception is thrown, I just would like to know a workaround. I tried

var productContained = shoppingCart.Select(sc => new
                    {
                        scId = sc.Id,
                        productName = _ProductRepository.GetProductName(sc.Id)
                    });

searchShoppingCart = shoppingCart.Where(sc => sc.Id.Equals(productContained.Where(pc => pc.productName.Equals(productName))
                                                                           .Select(pc => pc.Id)));

但是它给了我同样的例外.还有其他解决方法吗?

but it gives me the same exception. Is there any other workaround?

更新

抛出的异常是

LINQ to Entities无法识别方法'System.String GetProductName(Int32)'，并且该方法无法转换为商店表达式.

推荐答案

它会引发异常，因为它试图将您的代码转换为SQL(并且无法执行).阅读本文以了解一些解决方法: http://thoai- nguyen.blogspot.it/2011/05/custom-function-entity-framework.html

It throws an exception because it tries to convert your code to SQL (and it can't do it). Read this article for some workarounds: http://thoai-nguyen.blogspot.it/2011/05/custom-function-entity-framework.html

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