How can I turn a lambda expression specifying a property into an asp.net mvc compatible 'name' string representing the same?

Question

Assume

string value = ViewModelObject.SomeList[n].AnotherList[m].SomeProperty.ToString() //value is '5'

I need to turn this:

Expression<Func<ViewModelObjectType, object>> exp = x => x.SomeList[n].AnotherList[m].SomeProperty

into

<input type='hidden' name='SomeList[n].AnotherList[m].SomeProperty' value='5'/>

where n and m are integers.

I'm betting someone's solved this before. I want to bind my javascript control to my page viewmodel in a type safe manner. I'm playing around with the expression classes now and I can extract the property as a string but the rest of it I haven't figured out yet.

Thanks!

Are you sure you want `name` to be `"SomeList[n]..."` instead of `"SomeList[0]..."`, e.g.? — StriplingWarrior, Jan 01 '15 at 23:08
I know. But MVC generally binds well when you have property names that have constant integer values in the `name` property in HTML, instead of variable names. — StriplingWarrior, Jan 01 '15 at 23:13
I'm going to add the so I can break free of the stiff index requirements, actually — Isaac Bolinger, Jan 01 '15 at 23:21
The idea was to have my javascript control generate its own hidden inputs and keep them updated as the page changes. Sometimes they are deleted and in this case I wouldn't have to worry about regenerating inputs belonging to other controls of the same type. — Isaac Bolinger, Jan 01 '15 at 23:26

Darin Dimitrov · Accepted Answer · 2015-01-01T23:18:36.297

4

The @Html.HiddenFor helper seems to do what you need:

@Html.HiddenFor(x => x.SomeList[n].AnotherList[m].SomeProperty)

But if for some reason you cannot rely on what's already built into the framework you could always roll your own stuff using the ExpressionHelper.GetExpressionText method which is what the ASP.NET MVC built-in helpers are already using:

public static class HtmlExtensions
{
    public static string Foo<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> ex)
    {
        return ExpressionHelper.GetExpressionText(ex);
    }
}

and then in your strongly typed view use it like that:

<input type='hidden' name='@Html.Foo(x => x.SomeList[n].AnotherList[m].SomeProperty)' value='5'/>

edited Jan 01 '15 at 23:18

answered Jan 01 '15 at 23:10

Darin Dimitrov

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Yes I was looking for a way around hidden for. I have some black magic to work. – Isaac Bolinger Jan 01 '15 at 23:20
Well, in this case you might also try the `ExpressionHelper.GetExpressionText` method as shown in my answer. But I'd rather try to fight the black magic at its root rather than extending it. – Darin Dimitrov Jan 01 '15 at 23:20
indeed, you've been a great help. I don't want to fiddle with the expression classes. – Isaac Bolinger Jan 01 '15 at 23:23

score 1 · Answer 2 · edited May 23 '17 at 12:05

I had to use this courtesy of: ExpressionHelper.GetExpressionText(expression) not returning the name of my property

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);
}

My NodeType was always evaluating as ExpressionType.Convert

How can I turn a lambda expression specifying a property into an asp.net mvc compatible 'name' string representing the same?

2 Answers2