feature: job exporting (resolves #155)

Disco.Web.Extensions/Disco.Web.Extensions.csproj

@@ -111,6 +111,7 @@
     <Compile Include="MvcExtensions\PartialCompiled\PartialCompiledHtmlExtensions.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="MvcExtensions\XmlResult.cs" />
+    <Compile Include="RazorExtensions\DropDownListExtensions.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Disco.BI\Disco.BI.csproj">

Disco.Web.Extensions/RazorExtensions/DropDownListExtensions.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Web.Mvc.Html;
+using System.Web.Mvc;
+
+namespace Disco.Web.Extensions
+{
+    public static class DropDownListExtensions
+    {
+        public static MvcHtmlString DropDownListFor<TModel, TObject, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, Func<TModel, IEnumerable<TObject>> source, Func<TObject, string> valueGenerator, Func<TObject, string> textGenerator, string instructionMessage = null)
+        {
+            var selectList = source(htmlHelper.ViewData.Model)
+                .Select(i => new SelectListItem() { Value = valueGenerator(i), Text = textGenerator(i) });
+
+            if (instructionMessage != null)
+            {
+                selectList = new SelectListItem[]
+                    { new SelectListItem { Text = instructionMessage, Value = string.Empty } }
+                    .Concat(selectList);
+            }
+
+            return htmlHelper.DropDownListFor(expression, selectList);
+        }
+    }
+}