ExpressionHelper.GetExpressionText(expression) not returning the name of my property

Question

I have implemented a MVC Extension to format the numbers in my application. It is based off the code found here. And is as follows

public static MvcHtmlString DecimalBoxFor<TModel>(this HtmlHelper<TModel> html, Expression<Func<TModel, double?>> expression, string format, object htmlAttributes = null)
{
    var name = ExpressionHelper.GetExpressionText(expression);   
    double? dec = expression.Compile().Invoke(html.ViewData.Model);
    var value = dec.HasValue ? (!string.IsNullOrEmpty(format) ? dec.Value.ToString(format) : dec.Value.ToString()): "";
    return html.TextBox(name, value, htmlAttributes);
}

When I call it with the following line of Razor syntax

@Html.DecimalBoxFor(model => Model.PointAttributes[i].Data.Y,"0.000", new { @class = "span1 number" })

I get an exception because the variable 'name' in my extension is an empty string. I have tried changing the var name line to this but it only gives me the property name of 'Y' and not the full 'Model.PointAttributes[i].Data.Y' that I need to bind the model back for MVC.

var name = ((expression.Body is MemberExpression ?((MemberExpression)expression.Body).Member : ((MemberExpression)((UnaryExpression)expression.Body).Operand).Member)).Name;

score 9 · Answer 1 · answered Feb 20 '13 at 13:59

9

Try using this function:

    static public string GetExpressionText(LambdaExpression p)
    {
        if (p.Body.NodeType == ExpressionType.Convert || p.Body.NodeType == ExpressionType.ConvertChecked)
        {
            p = Expression.Lambda(((UnaryExpression)p.Body).Operand,
                p.Parameters);
        }
        return ExpressionHelper.GetExpressionText(p);
    }

answered Feb 20 '13 at 13:59

Nadav

357
3
10

1

This answer led me to the solution, and I created/released [Mariuzzo.Web.Mvc.Extras](https://github.com/rmariuzzo/Mariuzzo.Web.Mvc.Extras) – Rubens Mariuzzo Feb 21 '13 at 14:36

score 7 · Accepted Answer · answered Feb 21 '13 at 14:35

7

This is a known behavior. I have figured out writing my own version of ExpressionHelper that handle that specific case. Now you have two option:

Use the NuGet package:

Install-Package Mariuzzo.Web.Mvc.Extras

Or just grab the source code of the aforementioned ExpressionHelper and glue it into your project.

answered Feb 21 '13 at 14:35

Rubens Mariuzzo

28,358
27
121
148

Thanks @AarolamaBluenk, I will take in account your suggestion, and will definitively improve myself. Thanks again. – Rubens Mariuzzo Mar 06 '13 at 19:59
We ran into this and this worked perfectly for us. Thank you! – Chris Barr Sep 27 '13 at 19:52

score 3 · Answer 3 · edited May 23 '17 at 11:53

Here a 'hybrid' one :)

    public static void AddModelError<TModel>(this ModelStateDictionary state, Expression<Func<TModel, object>> expression, string message)
    {
        LambdaExpression lambdaExpression = null;
        string fieldName = string.Empty;

        if (expression.Body.NodeType == ExpressionType.Convert || expression.Body.NodeType == ExpressionType.ConvertChecked)
        {
            lambdaExpression = Expression.Lambda(((UnaryExpression)expression.Body).Operand, expression.Parameters);
            fieldName = ExpressionHelper.GetExpressionText(lambdaExpression);
        } else {
            fieldName = ExpressionHelper.GetExpressionText(expression);
        }

        state.AddModelError(fieldName, message);
    }

This one is more compact and probably a better solution:

https://stackoverflow.com/a/12689563/951001

user1433194 · Answer 4 · 2012-06-03T05:54:23.187

0

If you can get away without using a nullable type it seems to work (i.e. remove the ? after double, or as in my case decimal). So

Expression<Func<TModel, double?>>

becomes

Expression<Func<TModel, double>>.

If you step through it with the nullable type in place you'll see the expression has a convert() function in it which seems to be the 'problem'. I'm sure like me you would be interested in how to make this function work for nullable types as well.

edited Jun 03 '12 at 05:54

answered Jun 03 '12 at 05:43

user1433194

23
1
4

Unfortunately it needs to be a nullable type. – PlTaylor Nov 24 '12 at 22:01

score 0 · Answer 5 · answered Aug 23 '13 at 11:29

I know it's closed but for the record;

That's better handled by a template so you can specify what datatype you are using in the model and how it is represented in the template (single responsability). Also you won't need to modify the MVC framework.

MSDN UiHint attribute

ExpressionHelper.GetExpressionText(expression) not returning the name of my property

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