新对象的表达式树 [英] Expression tree for new object

问题描述

I'm trying to dynamically create an expression for a new object but I can't figure out how to do it.

void DoWork(Type t)
{

    //do some work to figure out which properties I want to use
    List<PropertyInfo>() props = (from p in t.GetProperties()
                                    where p.HasAttribute(MyAttribute)
                                    select p).ToList();

    //now I want to create a lambda expression that's like:  (x=> new {x.Prop1, x.Prop2, ...})
    //for each property in the list props

    //create parameter
    var param = Expression.Parameter(t,"t");
    //get list of expressions for properties
    var initValues = (from p in props
                        select Expression.PropertyOrField(param, p.Name)).ToList();

    //build expression body
    Expression body = Expression. //I have no idea what to do here

    //create lambda
    dynamic propLambda = Expression.Lambda(body, param);

    //use it!  MyFunction( x=> new {x.Prop1, x.Prop2,...});
    MyFunction(lambda);

}

推荐答案

这样的事情应该有效：

Something like this should work:

void DoWork(Type t)
{
    var param = Expression.Parameter(t, "t");
    
    var returnValue = Expression.New(t);
    
    var initValues = from p in t.GetProperties()
        where p.HasAttribute(MyAttribute)
        let value = Expression.Property(param, p)
        select Expression.Bind(p, value);
    
    var body = Expression.MemberInit(returnValue, initValues);
    
    var propLambda = Expression.Lambda(body, param);
    
    MyFunction(propLambda);
}

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