将表达式转换为另一个？ [英] Converting expression to another?

问题描述

我有一个小挑战，我不知道该如何解决。

我需要从此 Expression< Func< TEntity，URequest，bool>> 转换为此 Expression< Func< TEntity，bool>> 。

第二个将用于查询数据源。

这个想法是让它具有一个带有以下签名的基类构造函数

 抽象类Base 
 {
 Base（Expression< Func< TEntity，TRequest，bool>>表达式）{....} 
} 
  

我可以在派生类中提供这样的表达式

  class Derived：Base 
 {
 Derived（）：
 base（（enttiy，request）=> entity.SomeProp == request.SomePropValue）{} 
} 
  

基地以此方式使用

  /// Ctor 
 Base（Expression< Func< TEntity，TRequest，bool>表达式）
 {
 _pipelineBuilder.AddFetchEntityStep（表达式）
} 
  

AddFetchEntityStep是管道中的步骤

管道如下所示。

步骤1：FetchEntity
步骤2：执行
步骤3：验证
步骤3 ：已执行

现在，有两种方法可以通过ID或其他属性来检索实体。

为此，我有

  ReadOnlyRepository 
 { 
 TEntity GetById< TEntity>（对象ID）{....} 
 TEntity GetBy< TEntity>（Expression< Func< TEntity，bool>"表达式）{....} 
  

在AddFetchEntityStep中，我进行了一次检查以了解要调用什么，类似于

  public void AddFetchEntityStep（表达式< Func< TEntity，URequest，bool>"表达式= null）
 {
 if（expression == null）
 {
 _repo.GetById< TEntity>（1）
} 
 
否则
 {
 _repo.GetBy（。 ....）////问题
} 
} 
  

我知道它们是两个不同的签名
Expression< Func< TEntity，bool>> 和 Expression< Func< TEntity，TRequest，bool> ;>

解决方案

您不能简化

只要使用lambda表达式的调用者未提供request参数，请考虑使用 Func< URequest，Expression< Func< TEntity，bool>>> 而不是 Expression< Func< TEntity，URequest，bool>> 。

lambda表达式看起来像这样

（请求） => （完整）=> entity.SomeProp == request.SomePropValue 。

然后，您的基类可以调用它来将 request对象绑定到表达式。 / p>

顺便说一句，前缀不是 T 的通用参数名称是反模式。

I have a little challenge which I don't know how to solve.

I need to convert from this Expression<Func<TEntity, URequest, bool>> to this Expression<Func<TEntity, bool>>.

The 2nd is going to be used to query a data source.

The idea is this having a base class constructor with the following signature

abstract class Base
{
    Base(Expression<Func<TEntity, TRequest, bool>> expression) { .... }
}

I can provide an expression in the derived something like this

class Derived : Base 
{
   Derived() : 
        base ((enttiy, request) => entity.SomeProp == request.SomePropValue) { } 
}

This is used by the Base as such

/// Ctor
Base(Expression<Func<TEntity, TRequest, bool>> expression)
{
    _pipelineBuilder.AddFetchEntityStep (expression)
}

Where AddFetchEntityStep is a step in a pipeline

The pipeline looks like this.

Step 1 : FetchEntity Step 2 : Executing Step 3 : Validate Step 3 : Executed

Now there are two ways of retrieving an entity by Id or by another property.

For this I have a

ReadOnlyRepository
{
    TEntity GetById<TEntity>(object id) { .... } 
    TEntity GetBy<TEntity>(Expression<Func<TEntity, bool>> expression) { .... }

In the AddFetchEntityStep I do a check in order to know what Get to invoke, something like

public void AddFetchEntityStep (Expression<Func<TEntity, URequest, bool>> expression = null)
{
     if (expression == null )
     {   
         _repo.GetById<TEntity>(1)
     }  

     else 
     {
         _repo.GetBy(.....) //// The problem 
     }
}

I know they are two different signatures Expression<Func<TEntity,bool>> and Expression<Func<TEntity, TRequest, bool>>

解决方案

You cannot simply use lambda expression to convert an expression tree to another.

As long as the request parameter is not provided by the caller that specifies lambda expression , consider use Func<URequest,Expression<Func<TEntity,bool>>> instead of Expression<Func<TEntity, URequest, bool>>.

And the lambda expression would look like this

(request) => (enttiy) => entity.SomeProp == request.SomePropValue.

Then your base class could call it to bind a 'request' object to the expression.

Btw, generic parameter names with prefix other than T is antipattern.

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