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
– StriplingWarrior, Commented Jan 1, 2015 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
– StriplingWarrior, Commented Jan 1, 2015 at 23:13
I'm going to add the <input type=hidden name="foo.bar.Index" value='weirdindexvalue' /> so I can break free of the stiff index requirements, actually — Isaac Bolinger
– Isaac Bolinger, Commented Jan 1, 2015 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
– Isaac Bolinger, Commented Jan 1, 2015 at 23:26

Darin Dimitrov · Accepted Answer · 2015-01-01 23:18:36Z

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 1, 2015 at 23:18

answered Jan 1, 2015 at 23:10

Darin Dimitrov

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3 Comments

Isaac Bolinger Over a year ago

Yes I was looking for a way around hidden for. I have some black magic to work.

Darin Dimitrov Over a year ago

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.

Isaac Bolinger Over a year ago

indeed, you've been a great help. I don't want to fiddle with the expression classes.

Community · Accepted Answer · 2017-05-23 12:05:53Z

1

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

edited May 23, 2017 at 12:05

CommunityBot

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answered Jan 2, 2015 at 5:07

Isaac Bolinger

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