避免在Linq Select方法中重复代码 [英] Avoiding duplicate code in Linq Select method

问题描述

我有些愚蠢的情况，无法为烦人的问题找到简单而优雅的解决方案.

I have some stupid situation where I can't find simple and elegant solution for annoying problem.

我编写具有简单UI的asp.net应用程序，用于根据用户选择查询数据库.为了使用实体框架查询DB I.

I writing asp.net application with simple UI for querying database based on user choices. For querying DB I using Entity Framework.

在我的情况下，可选用户选择之一是自由文本，为此，我使用SQL Server FTS功能(使用

In my scenario, one of the optional user choices is a free text, and for that I using SQL Server FTS capabilities (using CONTAINSTABLE function, since I need to order results by relevance).

现在，我遇到以下情况:

Now, I have the following situation:

如果用户没有提供了自由文本条件，我将创建一个简单的Linq查询，其结果类型为IQueriable<Result>(其中"Result"是具有表中数据的实体)

If user did not provided free text criteria, I creating simple Linq query with result of type IQueriable<Result> (where 'Result' is an entity with data from table)

但是，如果用户 did 提供了自由文本条件，我将使用CONTAINSTABLE创建查询，其类型为IQueriable<ResultWithRank>(其中"ResultWithRank"是一个包含两个实体的对象:"Result"和排名"，因为CONTAINSTABLE会导致内部联接.

But, if user did provided free text criteria, I creating query with CONTAINSTABLE, and its type is IQueriable<ResultWithRank> (where 'ResultWithRank' is a object contains two entities: 'Result' and 'Rank', since CONTAINSTABLE results in inner join).

在此阶段，构建可查询对象后，需要在其上执行选择"方法，以将其转换为有用的东西.

At this stage, after I built my queriable, I need to execute 'Select' method on it, in order to convert it to something useful.

问题出在这里

在第一种情况下，我的select语句如下:

In first case, my select statement looks like this:

var result = queryable.Select(entity => /*.. about 20 lines of reshapying code .. */

在第二种情况下，它看起来像这样:

In second case, it looks like this:

var result = queryable.Select(entity.Result => /*.. about 20 lines of exactly the same reshapying code .. */

我想避免重复选择"代码，因为这两种情况都相同.我试图将其移至外部方法，但这未能执行，因为Linq试图将我的方法转换为SQL并显然失败了.

I want to avoid duplication of "select" code, because it identical for both cases. I tried to move it to external method, but this was failing to execute, since Linq was trying to convert my method to SQL and obviously failed.

如何在不重复选择"代码的情况下以一种优雅的方式解决此问题?

How I can resolve this problem in some elegant way, without duplicating 'select' code?

推荐答案

我会使用:

Expression<Func<Result, Foo>> conversion = result => { ... };

第一种情况:

var result = queryable.Select(conversion);

第二种情况:

var result = queryable.Select(entity => entity.Result)
                      .Select(conversion);

基本上可以同时执行两个投影，因此您的第一个投影(在第二种情况下)会使您陷入已经解决的情况.

Basically use the fact that you can perform two projections together, so that your first projection (in the second case) gets you into a situation you've already tackled.

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