ASP.NET

19-Sep-15 11:59

I am learning ASP and would like to ask you about confusion I have. I created a View based on a template - a List of some objects. Here is some code:

HTML

@model IEnumerable<MvcTestApplication1.Models.RestaurantReview>

@{
    ViewBag.Title = "Index";
}

<h2>Index</h2>

<p>
    @Html.ActionLink("Create New", "Create")
</p>
<table>
    <tr>
        <th>
            @Html.DisplayNameFor(model => model.Name)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.City)
        </th>
        <th>
            @Html.DisplayNameFor(model => model.Rating)
        </th>
        <th></th>
    </tr>

My question is:

- Typically when I want to refer to the object which was passed by controller I use Model (with capital M). But in above code, why model => model.Name, with small m is used? I would appreciate beginner like(elaborate) explanation.

- Also what is the type of model? With small m. How does it know model.Name exists?

modified 19-Sep-15 18:05pm.

Kornfeld Eliyahu Peter19-Sep-15 20:04

19-Sep-15 20:04

You just told the compiler the type of the model here:

HTML

@model IEnumerable<MvcTestApplication1.Models.RestaurantReview>

And it is small 'm' because 'model' is a keyword for Razor...

Skipper: We'll fix it.
Alex: Fix it? How you gonna fix this?
Skipper: Grit, spit and a whole lotta duct tape.

Member 1206160020-Sep-15 0:18

20-Sep-15 0:18

No

First of all like I said even though you told this to Razor

@model IEnumerable < MvcTestApplication1.Models.RestaurantReview >
you refer to model usually with: Model (capital M), isn't it???

And also Model, is of type IEnumerable, so how come Model.Name would work?
IEnumerable doesn't have Name attribute, etc. But again the code above uses model with small m.

modified 20-Sep-15 6:47am.

Kornfeld Eliyahu Peter20-Sep-15 0:56

20-Sep-15 0:56

Let make some order...

model is a keyword for Razor, so at the top line your have to write it lowercase (the way Razor defines it). The @ sign preceding it is only a sign for the HTML parser to switch to Razor there...

The parser is far more sophisticated than you think so when seeing a Class<t> (generics) like declaration it can resolve it to T and not to Class...So it knows about your actual type...

Inside the lambda expression the name is meaningless - you can call it blabla if you wish...

Now, for the Model (uppercase) version...It is used as a shortcut for the actual instance of your model data (after all you didn't assigned to it a variable name when defining it at @model, so the engine added a name for you - Model...)

Skipper: We'll fix it.
Alex: Fix it? How you gonna fix this?
Skipper: Grit, spit and a whole lotta duct tape.

Member 1206160020-Sep-15 1:34

20-Sep-15 1:34

Now, for the Model (uppercase) version...It is used as a shortcut for the actual instance of your model data (after all you didn't assigned to it a variable name when defining it at @model, so the engine added a name for you - Model...)

This I understand - Model refers to the list of objects which I passed to this view right?

But everything else like I said I don't understand ....
what is model? (with small m)
I thought only Model was used? (with capital m) etc.

Kornfeld Eliyahu Peter20-Sep-15 1:57

20-Sep-15 1:57

Do you refer to model (small m) that inside the lambda here?

HTML

@Html.DisplayNameFor(model => model.Name)

You can call it blabla as I told...it has no meaning!

HTML

@Html.DisplayNameFor(blabal => blabla.Name)

To understand the actual syntax, look here: https://msdn.microsoft.com/en-us/library/system.web.mvc.html.displaynameextensions.displaynamefor(v=vs.118).aspx#M:System.Web.Mvc.Html.DisplayNameExtensions.DisplayNameFor``2%28System.Web.Mvc.HtmlHelper{System.Collections.Generic.IEnumerable{``0}},System.Linq.Expressions.Expression{System.Func{``0,``1}}%29[^]

Skipper: We'll fix it.
Alex: Fix it? How you gonna fix this?
Skipper: Grit, spit and a whole lotta duct tape.

Member 1206160020-Sep-15 2:57

20-Sep-15 2:57

You can call it blabla as I told...it has no meaning!
Yeah but how it knows it should display string "Name", "City", etc. as titles of the table then?

Kornfeld Eliyahu Peter20-Sep-15 3:11

20-Sep-15 3:11

You actually ask how the IDE knows that your model inner type has properties by that name, so when you type . (dot) you can write the names...
1. The IDE actually compiles your code
2. You gave the context of your type in the line of @modle
3. The DisplayNameFor method has two overrides, one for IEnumerable<t> and one for T, as T is known there is no problem to let you use intellisense...

Skipper: We'll fix it.
Alex: Fix it? How you gonna fix this?
Skipper: Grit, spit and a whole lotta duct tape.

Member 1206160020-Sep-15 3:41

20-Sep-15 3:41

As in my original question, what is there model and what is Model?? (when used inside html - not in the first line I mean)

F-ES Sitecore20-Sep-15 1:12

F-ES Sitecore

20-Sep-15 1:12

When referring to the model passed to the view you use Model. Your DisplayFor is an extension that works on the current model object and it uses a lambda expression to say what property you are interested in, with the "model => model.Name" being the expression. The way expressions work is you pick a variable that is used to refer to the object, that's the bit before the =>. Anything after the => you can use that variable. The variable can be anything though, the reason model.Name is working for you is because you called the variable model. This code is just as valid

@Html.DisplayNameFor(xyz => xyz.Rating)

In that case xyz is the same type as your model and Rating is the property on your model.

Your code isn't valid though as your model is an IEnumerable which doesn't have properties like name etc. If you want to get the header row for your data, you can do something like

@Html.DisplayNameFor(model => model.First().Name)

"model" is your IEnumerable so you're accessing the Name property of the first item in your IEnumerable which will be a RestaurantReview type. Note this will fail if you don't have any items in your model, so check the model isn't empty first.

Member 1206160020-Sep-15 1:38

20-Sep-15 1:38

Your code isn't valid though as your model is an IEnumerable which doesn't have properties like name etc. If you want to get the header row for your data, you can do something like

That is my point!! The code is valid though because it was generated by Visual Studio Template!!

I was also surprised if model (with small m) refers to IEnumerable, then how come model.Name makes sense? do you understand?

modified 20-Sep-15 9:46am.

Richard Deeming21-Sep-15 2:24

Richard Deeming

21-Sep-15 2:24

Looking at the documentation of the DisplayNameFor method[^], there are two overloads:

DisplayNameFor(HtmlHelper<TModel>, Expression<Func<TModel, TValue>>)
DisplayNameFor(HtmlHelper<IEnumerable<TModel>>, Expression<Func<TModel, TValue>>)

In this case, since your model is IEnumerable<RestaurantReview>, you're calling the second overload.

That overload takes a function which accepts a single item from your enumerable sequence, and returns one of its properties.

So in the code you've posted, model refers to a single RestaurantReview instance, not the IEnumerable<RestaurantReview> represented by the Model.

The naming convention is slightly confusing - it might have made more sense to have:

Html.DisplayNameFor(item => item.Name)

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Member 1206160021-Sep-15 2:50

21-Sep-15 2:50

Thanks finally I have heard something that is close to a reasonable explanation. Please add further details, if you like.

Member 1206160021-Sep-15 2:56

21-Sep-15 2:56

By the way if I do this:

HTML

<th>            @Html.DisplayNameFor(model => model.name)</th>

Where

HTML

@using TestMVCApplication.Models

<!--Declare that we will use this model.-->
@model List<Product>

I get

Compilation Error

C++

Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. 

Compiler Error Message: CS1061: 'System.Collections.Generic.List<TestMVCApplication.Models.Product>' does not contain a definition for 'name' and no extension method 'name' accepting a first argument of type 'System.Collections.Generic.List<TestMVCApplication.Models.Product>' could be found (are you missing a using directive or an assembly reference?)

Why?

PS Product has that property though

Richard Deeming21-Sep-15 3:19

Richard Deeming

21-Sep-15 3:19

I think the problem is that the generic HtmlHelper<TModel> class is not covariant. Therefore, you can't cast an instance of HtmlHelper<List<Product>> to HtmlHelper<IEnumerable<Product>>.

In this case, the model parameter will be the same type as the Model - ie: List<Product> - so you'll need to use FirstOrDefault in the lambda expression:

@Html.DisplayNameFor(model => model.FirstOrDefault().name)

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Member 1206160021-Sep-15 4:31

21-Sep-15 4:31

One more question. Why here

HTML

@Html.DisplayNameFor(model => model.name)

The title (e.g. "Name") of the property is printed on my web page instead of value of property?

Richard Deeming21-Sep-15 6:14

Richard Deeming

21-Sep-15 6:14

Because you're using DisplayNameFor. When you want to display the value, you use DisplayFor.

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Member 1206160021-Sep-15 8:41