将节点/属性添加到表达式树 [英] Adding a node/property to an Expression Tree

问题描述

这是我第一次真正处理过表达式树，我有点迷茫.我很抱歉 这个问题根本没有任何意义.请考虑以下类:

This is the first time I've really dealt with Expression Trees, and I am a bit lost. I apologise if this question just doesn't make any sense at all. Consider the following classes:

public class Foo<T> {
    public T Value { get; set; }
    public bool Update { get; set;}
}

public class Bar {
    public Foo<bool> SomeBool { get; set; }
    public Foo<string> SomeString { get; set; }
}

所以现在我有一个如下所示的辅助方法:

So right now I have a helper method that looks like this:

public void Helper<T>(Expression<Func<Bar, Foo<T>>> baseExpression, Expression<Func<Bar, T>> valExpression, Expression<Func<Bar, bool>> updateExpression) 
{
    // Do some stuff with those expressions.
}

然后像这样被调用:

Helper(b=>b.SomeBool,b=>b.SomeBool.Value,b=>b.SomeBool.Update);

但是我不喜欢构建三个几乎完全相同的表达式，并且必须显式地传递 他们进入助手.我更喜欢这样的东西:

But I dislike building three almost exact same expressions, and having to explicitly pass them into the Helper. What I would prefer is to something like this:

Helper(b=>b.SomeBool);

然后:

public void Helper<T>(Expression<Func<Bar, Foo<T>>> baseExpression) 
{
    // Do some stuff
    var valExpression = ???; // append `.Value` to baseExpression
    var updateExpression = ???; // append `.Update` to baseExpression
}

但是我不太确定该怎么做... 正确的方向会被错误地应用.

But I'm not really sure how to do that... Its boggling my mind, any shove in the right direction would be wildly appriciated.

推荐答案

可以；如果您有baseExpression，则类似于:

Sure; if you have baseExpression, then something like:

var valExpression = Expression.Lambda<Func<Bar, T>>(
    Expression.PropertyOrField(baseExpression.Body, "Value"),
    baseExpression.Parameters);
var updateExpression = Expression.Lambda<Func<Bar, bool>>(
    Expression.PropertyOrField(baseExpression.Body, "Update"),
    baseExpression.Parameters);

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