Getting Expression Text for lambda Expressions

Question

I have written a simple extension method for HtmlHelper class like

public static string GetExpressionNames<TModel>(this HtmlHelper<TModel> helper,params Expression<Func<TModel,object>>[] args) where TModel:class
        {
            string returnStr = string.Empty;
            int i = 0;
            foreach (var x in args) 
            {
                returnStr += (++i).ToString() + ExpressionHelper.GetExpressionText(x) + "<br/>";
            }
            return returnStr;
        }

Currently, it's just accepting array of LambdaExpressions defined on Model properties (returning object) and add their expression text to a string which is then returned by this function. The problem is that, for string type properties it's working fine, but for int properties it's returning the empty string as expression text. The reason is that for expression that returns int values the body of expression looks like following image:

enter image description here

but for strings, its like

enter image description here

I think convert method is expressions that return integar values is causing the empty string to be returned as Expression text. How can I get around this problem? I just need original expression text i.e Id for Convert(x.id) and Name for x.Name; it does not matter how it is processing it at the back end.

Are all of your expressions going to be simple or are they going to be nested? ie are you always expecting x=>x.Foo ? — Bob Vale
– Bob Vale, Commented Sep 16, 2011 at 14:12

Bob Vale · Accepted Answer · 2011-09-16 15:00:11Z

6

I have this extension method to do it for me

public static string GetMemberName(this LambdaExpression expr) {
  var lexpr = expr;
  MemberExpression mexpr = null;
  if (lexpr.Body is MemberExpression) {
    mexpr = (MemberExpression) lexpr.Body;
  } else if (lexpr.Body is UnaryExpression) {
    mexpr = (MemberExpression) ((UnaryExpression) lexpr.Body).Operand;
  }
  if (mexpr == null) {
    return null;
  }
  return mexpr.Member.Name;
}

You may want to consider putting extra checks as if Convert doesn't containt a memberexpression you will get a cast error.

answered Sep 16, 2011 at 15:00

Bob Vale

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Comments

StriplingWarrior · Accepted Answer · 2011-09-16 14:11:33Z

1

Your question isn't complete enough for me to know whether you need to handle more complex scenarios (method calling, addition, etc), but if you're just expecting the expression to contain a property, and you just want the property's name, you could write code that looks into the Body of the lambda expression itself. If the body is a Convert expression, you could look at the inner expression. Then pull the property's name off of the MemberAccess expression inside that.

answered Sep 16, 2011 at 14:11

StriplingWarrior

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1 Comment

StriplingWarrior Over a year ago

@Muhammed: Bob Vale's answer is what I have in mind. Feel free to accept his.

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