MVC3 razor based htmlhelper with lambda field expressions based on model

Question

I am creating a fluent HtmlHelper in MVC - to create a grid based on HTML. I am aware of mvc contrib and WebGrid - but I am making my own and have a specific problem:

I have to enter this:

@Html.DSGridFor().AddColumn(x=>x.FirstOrDefault().Message)

but I want to be able to type this:

@Html.DSGridFor().AddColumn(x=>x.Message)

The code that gets called when I start with @Html.DSGridFor() - taking in the page based model.

public static DSGridHelper<TModel> DSGridFor<TModel>(this HtmlHelper<TModel> html)
{
   return new DSGridHelper<TModel>(html);
}

and then within the class DSGridHelper I have this:

public DSGridHelper<TModel> AddColumn(Expression<Func<TModel, dynamic>> property, string HeaderText = null)
        {
            string ColumnName = (property.Body as MemberExpression).Member.Name;

            DSGridColumn DSGC = new DSGridColumn();
            DSGC.ColumnName = ColumnName;
            DSGC.HeaderText = HeaderText ?? ColumnName;
            DSColumnList.Add(DSGC);

            return this;
        }

public List<DSGridColumn> DSColumnList { get; set; }

and the column class at the moment is really basic:

  public class DSGridColumn
    {
        public DSGridColumn()
        {

        }

        public string ColumnName { get; set; }
        public string HeaderText { get; set; }

    }

I can get this code working fine with string based column names, but I want the declaring code in the razor page to be simple in format and strongly typed. At the moment I have to type x=>x.First().Message but I really only need x=>x.Message to identify the column.

I appreciate any help.

UPDATE

Thanks to Justin I can now provide my/our code.

View:

@(Html.DSGridFor3().AddColumn(x => x.Message)
                   .AddColumn(x => x.Host)
                   .ToMvcString())

HTML Helper call:

public static DSGridHelper3<T> DSGridFor3<T>(this HtmlHelper<IEnumerable<T>> htmlHelper)
{
         return new DSGridHelper3<T>(htmlHelper);
}

Returning class:

public class DSGridHelper3<T>
    {
        private HtmlHelper _htmlHelper;
        //private IEnumerable<T> _dataList;
        public List<DSGridColumn> DSColumnList { get; set; }

        public DSGridHelper3(HtmlHelper<IEnumerable<T>> htmlHelper)
        {
            _htmlHelper = htmlHelper;
           // _dataList = htmlHelper.ViewData.Model;
            DSColumnList = new List<DSGridColumn>();
        }

        public DSGridHelper3<T> AddColumn(Expression<Func<T, object>> property)
        {
            string columnName = (property.Body as MemberExpression).Member.Name;
            DSGridColumn DSGC = new DSGridColumn();
            DSGC.ColumnName = columnName;
            DSGC.HeaderText = columnName;
            DSColumnList.Add(DSGC);

            return this;
        }

        public MvcHtmlString ToMvcString()
        {
            sb.Append("<table>");
            sb.Append("<tr>");
            sb.Append("<td>");
            sb.Append("hello world within a table");
            sb.Append(@"</td>");
            sb.Append("<td>");
            sb.Append("hello world within a table");
            sb.Append(@"</td>");
            sb.Append(@"</tr>");
            sb.Append(@"</table>");


            return new MvcHtmlString(sb.ToString());

        }
    }

UPDATE 2

If you wanted to manually insert a different type (perhaps because you are going to get a small amount of table data from ViewData rather than the model of the page) then here is some more code:

View:

@(Html.DSGridFor3<DanSoftware.MVC.Areas.Errors.Code.ELMAH_Error>().AddColumn(x => x.Message).ToMvcString();)

Alternative signature for the DSGridHelper ...helper

public static DSGridHelper3<T> DSGridFor3<T>(this HtmlHelper htmlHelper)
        {
            return new DSGridHelper3<T>(htmlHelper);
        }

Additional constructor:

public DSGridHelper3(HtmlHelper htmlHelper)
        {
            _htmlHelper = htmlHelper;
            // _dataList = htmlHelper.ViewData.Model;
            DSColumnList = new List<DSGridColumn>();
        }

Hope this helps someone and thanks Justin!

But here ye be warned - careful with the column name extraction - it doesn't work all the time. The database is basically the Elmah table. When trying to get the ErrorID the expression is actually {x => Convert(x.ErrorId)} which fails in the above code. SOLUTION WELCOME TO THIS TOO! — Dan B
– Dan B, Commented Jun 6, 2011 at 21:09
Opened a separate question here stackoverflow.com/questions/6269822/… — Dan B
– Dan B, Commented Jun 7, 2011 at 18:21

Justin Soliz · Accepted Answer · 2011-06-05 18:39:13Z

2

I dont have Visual Studio with me but I'll take a stab at this...

I would take in a collection as a datatype either in your DsGridFor method or in the AddColumn method. This will allow you to send Strongly-typed arguments from a collection. Say you wanted a generic method of AddColumn for a given collection with access to the class properties vs the collection methods, it would look something like this (just an example):

    public static DSGridHelper<T> AddColumn<T>(this HtmlHelper<IEnumerable<T>> htmlHelper, Expression<Func<T, object>> property) where T : class
    {
        string columnName = (property.Body as MemberExpression).Member.Name;

        DSGridColumn DSGC = new DSGridColumn();
        DSGC.ColumnName = ColumnName;
        DSGC.HeaderText = HeaderText ?? ColumnName;
        DSColumnList.Add(DSGC);

        return this;
    }

For your situation, to new-up a DsGridHelper class I might explicitly set a model-type first and then add overloads as I go:

    public static DSGridHelper<T> DSGridFor<T>(this HtmlHelper<IEnumerable<T>> htmlHelper) where T : class
    {
        return new DSGridHelper<T>(htmlHelper);
    }

And then my DsGridHelper might look something like this:

public class DsGridHelper<T>
{
    private HtmlHelper _htmlHelper;
    private IEnumerable<T> _dataList;

    public DsGridHelper(HtmlHelper<IEnumerable<T>> htmlHelper)
    {
        _htmlHelper = htmlHelper;
        _dataList = htmlHelper.ViewData.Model;
    }

    public DsGridHelper<T> AddColumn(Expression<Func<T, object>> property)
    {
        string columnName = (property.Body as MemberExpression).Member.Name;
        DSGridColumn DSGC = new DSGridColumn();
        DSGC.ColumnName = ColumnName;
        DSGC.HeaderText = HeaderText ?? ColumnName;
        DSColumnList.Add(DSGC);

        return this;
    }
}

edited Jun 5, 2011 at 18:39

answered Jun 5, 2011 at 18:32

Justin Soliz

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6 Comments

Dan B Over a year ago

Code is mostly working (SUPER) intellisense wise but struggling with an error when running it: The model item passed into the dictionary is of type 'System.Data.Objects.ObjectQuery1[System.String]', but this dictionary requires a model item of type 'System.Collections.Generic.IEnumerable1

Justin Soliz Over a year ago

I assume its somewhere in your grid class, maybe when you're adding your columns? I'd have to see a bit more of your code to see whats causing the issue.

Dan B Over a year ago

SUCCESS! I was doing something very silly LOL. It helps if one passes the correct model type to the view. blush. I'll post my code in a sec. BTW - ur a genius!

Justin Soliz Over a year ago

Looks good, glad I could help. I'll take a look at the Elmah issue you're having.

Dan B Over a year ago

One more question I have just thought of - how would I best pass a different model into the implementation you have helped me out with? I may have two tables (maybe a smaller one) that I add to the page using ViewData rather than the model. Thank you once again Justin!

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