Question

Similar to question How can I get property name strings used in a Func of T.

Let’s say I had a lambda expression
stored like this in a variable called “getter”

Expression<Func<Customer, string>> productNameSelector =
    customer => customer.Product.Name;

how can I extract the string “Product.Name” from that?

I now fixed it somewhat haxy with

var expression = productNameSelector.ToString();
var token = expression.Substring(expression.IndexOf('.') + 1);

But i’d like to find a more solid way 😉

Answer 1

The expression tree for your expression looks like this:

           .
          / \
         .   Name
        / \
customer   Product

As you can see, there is no node that would represent Product.Name. But you can use recursion and build the string yourself:

public static string GetPropertyPath(LambdaExpression expression)
{
    return GetPropertyPathInternal(expression.Body);
}

private static string GetPropertyPathInternal(Expression expression)
{
    // the node represents parameter of the expression; we're ignoring it
    if (expression.NodeType == ExpressionType.Parameter)
        return null;

    // the node is a member access; use recursion to get the left part
    // and then append the right part to it
    if (expression.NodeType == ExpressionType.MemberAccess)
    {
        var memberExpression = (MemberExpression)expression;

        string left = GetPropertyPathInternal(memberExpression.Expression);
        string right = memberExpression.Member.Name;

        if (left == null)
            return right;

        return string.Format("{0}.{1}", left, right);
    }

    throw new InvalidOperationException(
        string.Format("Unknown expression type {0}.", expression.NodeType));
}