Question

Background

.NET 4, C#, MVC3, using JsonFx to serialize and deserialize data. Base controller has been extended to intercept all requests and do the following:

1. Get some JSON from a remote server.
2. Run a LINQ query based on passed in keys (hero, body, footer).
3. Return a generic model to the view.

This code works fine when running in a controller inheriting from the base controller, but when placed in the Base controller and called from an inherited controller, I get the following error:

Unable to cast object of type 'System.Linq.Expressions.ConstantExpression' to type 'System.Linq.Expressions.ParameterExpression'.

This is the offending line:

    var queryHero = heroModel.ArrayItems().Where(o => o.DisplayName == keyHero);

Question

How do I avoid getting a type error when in the base controller? It’s the same code that runs fine in the inherited controller.

Thanks for your time.

Full Code

public models.GenericPageModel GetGenericPageContent(string keyHero, string keyBody, string keyFooter)
{
    try
    {
        // get content "tables"
        var heroContent = GetJson("Page_Section_Hero_Content");
        var bodyContent = GetJson("Page_Section_Body_Content");
        var footerContent = GetJson("Page_Section_Footer_Content");

        // new reader
        var reader = new JsonReader(new DataReaderSettings(new DataContractResolverStrategy()));

        // read it
        var heroModel = reader.Query<models.PageSectionHeroContent>(heroContent);
        var bodyModel = reader.Query<models.PageSectionBodyContent>(bodyContent);
        var footerModel = reader.Query<models.PageSectionFooterContent>(footerContent);

        // run query for current page
        var queryHero = heroModel.ArrayItems().Where(o => o.DisplayName == keyHero);
        var queryBody = bodyModel.ArrayItems().Where(o => o.DisplayName == keyBody);
        var queryFooter = footerModel.ArrayItems().Where(o => o.DisplayName == keyFooter);

        // models for return
        models.PageSectionHeroContent hero;
        models.PageSectionBodyContent body;
        models.PageSectionFooterContent footer;

        // any hero content?
        if (queryHero.Any())
            hero = new models.PageSectionHeroContent { DisplayName = queryHero.FirstOrDefault().DisplayName, 
                ContentXML = queryHero.FirstOrDefault().ContentXML };
        else
            hero = new models.PageSectionHeroContent { DisplayName = "Sorry, there was an error.", 
                ContentXML = "<details><error>No data was returned.</error></details>" };

        // any body content?
        if(queryBody.Any())
            body = new models.PageSectionBodyContent { DisplayName = queryBody.FirstOrDefault().DisplayName, 
                ContentXML = queryBody.FirstOrDefault().ContentXML };
        else
            body = new models.PageSectionBodyContent { DisplayName = "Sorry, there was an error.", 
                ContentXML = "<details><error>No data was returned.</error></details>" };

        // any footer content?
        if(queryFooter.Any())
            footer = new models.PageSectionFooterContent { DisplayName = queryFooter.FirstOrDefault().DisplayName, 
                ContentXML = queryFooter.FirstOrDefault().ContentXML };
        else
            footer = new models.PageSectionFooterContent { DisplayName = "Sorry, there was an error.", 
                ContentXML = "<details><error>No data was returned.</error></details>" };

        // build generic page model
        var model = new models.GenericPageModel { PageSectionHeroContent = hero, PageSectionBodyContent = body, PageSectionFooterContent = footer };

        return model;

    }
    catch (Exception ex)
    {   
        //todo: handle, log exception
        return null;
    }
}

Answer 1

Can’t be sure what it is that is NOT initializing on time in the BaseController, but found a work-around.

DISCLAIMER: I am on the same dev team as boynamedjib and this solution may be suited the best for our particular situation. Having said that, the solution is worth posting, we feel, as it might help others who encounter this quirk.

Solution

The solution was found in making use of a combination of dynamic types and ExpandoObjects that are specific to C# 4.0, as well as the IDictionary type.

 public models.GenericPageDataModel GetGenericPageContent(string keyHero, string keyBody, string keyFooter)
        {
            try
            {
                var pageData = new List<models.GenericPageData>
                             {
                                 new models.GenericPageData{Key = "HeroModel",Value = GetJson("pro_Page_Section_Hero_Content")},
                                 new models.GenericPageData{Key = "BodyModel",Value = GetJson("pro_Page_Section_Body_Content")},
                                 new models.GenericPageData{Key = "FooterModel",Value = GetJson("pro_Page_Section_Footer_Content")}
                             };

                var reader = new JsonReader();

                var model = new models.GenericPageDataModel();
                foreach (var p in pageData)
                {
                    var objList = new List<ExpandoObject>();
                    dynamic output = reader.Read(p.Value);
                    foreach (var h in output)
                    {
                        dynamic obj = new ExpandoObject();
                        foreach (dynamic o in h)
                        {
                            var item = obj as IDictionary<String, object>;
                            item[o.Key] = o.Value;
                        }
                        objList.Add(obj);
                    }
                    switch (p.Key)
                    {
                        case ("HeroModel"):
                            model.HeroModel = objList.FirstOrDefault(o => o.FirstOrDefault(i => i.Key.Equals("DisplayName")).Value.Equals(keyHero));
                            break;
                        case ("BodyModel"):
                            model.BodyModel = objList.FirstOrDefault(o => o.FirstOrDefault(i => i.Key.Equals("DisplayName")).Value.Equals(keyBody));;
                            break;
                        case ("FooterModel"):
                            model.FooterModel = objList.FirstOrDefault(o => o.FirstOrDefault(i => i.Key.Equals("DisplayName")).Value.Equals(keyFooter));;
                            break;
                        default:
                            break;
                    }
                }
                return model;
            }
            catch (Exception ex)
            {
                return null;
            }
        }

Supporting Models

public class GenericPageData
        {
            public string Key { get; set; }
            public string Value { get; set; }
        }

        public class GenericPageDataModel
        {
            public ExpandoObject HeroModel { get; set; }
            public ExpandoObject BodyModel { get; set; }
            public ExpandoObject FooterModel { get; set; }
        }

Razor Usage

@model my.project.com.Models.ContentModels.GenericPageDataModel        

@{
    ViewBag.Title = "My Title";
    Layout = "~/Views/Shared/_Layout.cshtml";

    ViewBag.heroDisplayName = @Model.HeroModel.ToDictionary(p => p.Key).FirstOrDefault(k => k.Key.Equals("DisplayName")).Value.Value;
}

<h1> @ViewBag.heroDisplayName</h1>