Combine Lambda Expressions

Question

I am looking for a way to combine two lambda expressions, without using an Expression.Invoke on either expression. I want to essentially build a new expression

Answer 1

Use a visitor to swap all instances of the parameter f to m.SubModel.Foo, and create a new expression with m as the parameter:

internal static class Program
{
    static void Main()
    {

        Expression> expression1 = m => m.SubModel.Foo;
        Expression> expression2 = f => f.Bar.Value;

        var swap = new SwapVisitor(expression2.Parameters[0], expression1.Body);
        var lambda = Expression.Lambda>(
               swap.Visit(expression2.Body), expression1.Parameters);

        // test it worked
        var func = lambda.Compile();
        Model test = new Model {SubModel = new SubModel {Foo = new Foo {
             Bar = new Bar { Value = "abc"}}}};
        Console.WriteLine(func(test)); // "abc"
    }
}
class SwapVisitor : ExpressionVisitor
{
    private readonly Expression from, to;
    public SwapVisitor(Expression from, Expression to)
    {
        this.from = from;
        this.to = to;
    }
    public override Expression Visit(Expression node)
    {
         return node == from ? to : base.Visit(node);
    }
}