Get the property name used in a Lambda Expression in .NET 3.5

Question

I have a problem that has been nagging me for some time now and I can't find the answer.

I need to obtain the name of the property that is being referenced in a Lambda Expression. I would provide the lambda expression to a method that would return a string. For example if I have:

x => x.WeirdPropertyName

then the method would return:

"WeirdPropertyName"

I have read that it can be done with expression trees, but the answer has eluded me.

Thanks for any help

Answer 1

Here you go:

string GetPropertyName<T>(Expression<Func<T>> property)
{
    var propertyInfo = (property.Body as MemberExpression).Member as PropertyInfo;
    if (propertyInfo == null)
    {
        throw new ArgumentException("The lambda expression 'property' should point to a valid Property");
    }
    return propertyInfo.Name;
}

Answer 2

I've got a pretty comprehensive answer here.

In addition to dealing with expressions like x => x.WeirdPropertyName, it can also deal with "extended" expressions such as x => x.WeirdMember.WeirdPropertyName.

Here's the code from that answer:

// code adjusted to prevent horizontal overflow
static string GetFullPropertyName<T, TProperty>
(Expression<Func<T, TProperty>> exp)
{
    MemberExpression memberExp;
    if (!TryFindMemberExpression(exp.Body, out memberExp))
        return string.Empty;

    var memberNames = new Stack<string>();
    do
    {
        memberNames.Push(memberExp.Member.Name);
    }
    while (TryFindMemberExpression(memberExp.Expression, out memberExp));

    return string.Join(".", memberNames.ToArray());
}

// code adjusted to prevent horizontal overflow
private static bool TryFindMemberExpression
(Expression exp, out MemberExpression memberExp)
{
    memberExp = exp as MemberExpression;
    if (memberExp != null)
    {
        // heyo! that was easy enough
        return true;
    }

    // if the compiler created an automatic conversion,
    // it'll look something like...
    // obj => Convert(obj.Property) [e.g., int -> object]
    // OR:
    // obj => ConvertChecked(obj.Property) [e.g., int -> long]
    // ...which are the cases checked in IsConversion
    if (IsConversion(exp) && exp is UnaryExpression)
    {
        memberExp = ((UnaryExpression)exp).Operand as MemberExpression;
        if (memberExp != null)
        {
            return true;
        }
    }

    return false;
}

private static bool IsConversion(Expression exp)
{
    return (
        exp.NodeType == ExpressionType.Convert ||
        exp.NodeType == ExpressionType.ConvertChecked
    );
}

Answer 3

The only way I know of getting the string name of a property is via reflection.