Replace a type in an expression tree

Question

I\'m struggling with the modification of an expression tree. I\'ve simplified the example to make it easier to display here. Let\'s start with two classes:

    p         


        

Answer 1

After some more searching I found the answer here: How to change a type in an expression tree?. It didn't show up in the suggestions when I submitted my question.

As I don't really need the Filter class, I instead created an interface with only the properties that I want to be able to filter (IEntity) and modified the Entity class to implement it. Now I'm able to get the desired results with this:

// Example use: return entities.Entities.Where(ExpressionTransformer.Transform(filter));
internal static class ExpressionTransformer where TTo : TFrom
{
    public class Visitor : ExpressionVisitor
    {
        private ParameterExpression _parameter;

        public Visitor(ParameterExpression parameter)
        {
            _parameter = parameter;
        }

        protected override Expression VisitParameter(ParameterExpression node)
        {
            return _parameter;
        }
    }

    public static Expression> Tranform(Expression> expression)
    {
        ParameterExpression parameter = Expression.Parameter(typeof(TTo));
        Expression body = new Visitor(parameter).Visit(expression.Body);
        return Expression.Lambda>(body, parameter);
    }
}

In case you need to do something similar but you cannot work with an interface or you cannot make your class implement that interface: the answer is also in the above mentioned answer