How do I use and ExpressionTree to access the name of the property in a lambda expression

Question

I'm using the following approach to get the name of a property specified in a lambda by inspecting the resulting ExpressionTree:

var name =GetPropertyName<Entity1, Entity2>(x => x.Entity2);

public string GetPropertyName<T, P>(Expression<Func<T, P>> expression)
    {
        var memberExpression = expression.Body as MemberExpression;
        var propertyInfo = memberExpression.Member as PropertyInfo;
        return propertyInfo.Name;
    }

//name is "Entity2"

Given the following expression i want to extract the names "Entity2s", "Entity3s" and "Entity4s"

var names = GetPropertyNames<Entity1, IEnumerable<Entity4>>(x => x.Entity2s.SelectMany(x => x.Entity3s).SelectMany(x  => x.Entity4s));

Answer 1

Here is a method for extracting the member names from exactly the Expression tree you provided. A more generic method should probably be based on an ExpressionVisitor subclass.

public static List<string> GetPropertyNames<T, P>(Expression<Func<T, P>> fe) {
    var ans = new List<string>();
    var callExpr1 = fe.Body as MethodCallExpression;
    var callExpr2 = callExpr1.Arguments[0] as MethodCallExpression;
    var e2MemberExpr1 = callExpr2.Arguments[0] as MemberExpression;
    ans.Add(e2MemberExpr1.Member.Name);
    var e2MemberExpr2 = (callExpr2.Arguments[1] as LambdaExpression).Body as MemberExpression;
    ans.Add(e2MemberExpr2.Member.Name);
    var e1MemberExpr1 = (callExpr1.Arguments[1] as LambdaExpression).Body as MemberExpression;
    ans.Add(e1MemberExpr1.Member.Name);
    return ans;
}