I was following this tutorial http://www.asp.net/mvc/tutorials/mvc-music-store
when I stumbled on this piece of code.
public ActionResult AddToCart(int id)
{
// Retrieve the album from the database
var addedAlbum = storeDB.Albums
.Single(album => album.AlbumId == id);
// Add it to the shopping cart
var cart = ShoppingCart.GetCart(this.HttpContext);
cart.AddToCart(addedAlbum);
// Go back to the main store page for more shopping
return RedirectToAction("Index");
}
I don't understand two things:
1)
var addedAlbum = storeDB.Albums
.Single(album => album.AlbumId == id);
What is this code doing? I don't know what the operator => does. Also I guess .Single is some function for the database?
2)
This function is having a call to itself? I don't see how it adds the album to the cart this way. Wouldn't this cause a function to go into an infinite loop?
It seems there are a lot of core C# that you aren't quite familiar with yet.
the => operator is the lambda operator, which is a succinct way of writing an inline function.
The Single function is an extension method which in this case is makes a call to the database. This method makes use of a neat feature known as expression trees to convert the strongly typed C# comparison into the corresponding SQL code. How it works is a pretty advanced topic, so for now just consider it "magic".
The AddToCart method of the cart object is different from the AddToCart controller action method the code is currently in. I don't have a link for that, since that's fairly basic object-oriented programming.
I would assume that cart.AddToCart will actually update the database.
Also read up on LINQ for a better understanding. This is most likely either Linq To Sql or LINQ to Entities using the Entity Framework.
The Action is being passed the ID of a album which can then be retrieved from the database with storeDB.Albums.Single() call. (the lambda is saying "find the entry in the database where the value in the AlbumId column matches the ID passed to the controller.") Think of .Single as the LINQ facsimile of:
SELECT TOP(1) *
FROM Albums
WHERE Albums.AlbumId = <id>
It's then grabbing the user's shopping cart and adding that fetched album object to the cart.
Then you're redirected to the index where it can list all entries in the cart.
Related
Let me explain the whole context:
I'm using ASP.NET MVC 2, EF4 (POCO).
I trying to do a generic repository for my app.
I'm having problem on updating a many to many relationship.
I have an item that is related to other by a many to many table. In the View, the user picks the desired Categories, and send just the chosen id's to the Controller.
Then, the Controller queries the Category Repository, adding it to the main item:
item.Categories.Add(CategoriesRepository.Single(id);
But, when I go the Repository and try to save like this:
Entities.ApplyCurrentValues(entity);
Context.SaveChanges();
But, the state of my entity is Added.
Then, I Cannot save my entity :(.
How can I solve this problem?
Thanks for your answers.
I have in the View, the following code:
<%= Html.CheckBoxList("Categories", ((IEnumerable<Categories>)ViewData["Categories"]).ToDictionary(c => c.ID.ToString(), c => c.Name)
, Model.Categories.ToDictionary(c => c.ID.ToString(),c => c.Name )) %>
Where CheckBoxList is a HTMLHelper.
Im putting the ids as values in the View, because I dont know other way to put and then get this information from the View.
How can I use the ObjectStateManager.ChangeRelationshipState method?
Like this? :
itemRepository.Db.ObjectStateManager.ChangeRelationshipState(item, item.Categories, "Categories", System.Data.EntityState.Modified);
I trying in this way, but it returns error.
Help! lol
You've got a few problems.
1) ApplyCurrentValues only works for scalar-properties. Since your trying to add a Category to the Categories navigational property on Item, this will not work.
2) You say this:
the user picks the desired Categories, and send just the chosen id's to the Controller.
How can your Controller accept a bunch of id's? How is this model binding done? We need more info on how your View is bound to your model, what's being passed to the action method. But it sounds like you need to redesign this particular View with the help of a ViewModel.
3) Change tracking with POCO's in MVC is a royal pain in the butt. In your scenario, you'll need to use ObjectStateManager.ChangeRelationshipState to manually set the Categories relationship to **Modified.
Honesty though, it's more pain than it's worth. I went through this same problem.
Cop it on the chin - go grab the entity first and use Controller.UpdateModel:
[HttpPost]
public ActionResult Item(Item item)
{
// get the existing item
var existingItem = ItemRepository.Single(item.Id);
// use MVC to update the model, including navigational properties
UpdateModel(existingItem);
// save changes.
Context.SaveChanges();
}
I'm trying to design a solution in MVC in which a string representation of a class is passed to the controller which should then build a grid with all the data belonging to that class in the DB. (I'm using an ORM to map classes to tables).
//A method in the Model that populates the Item Property
foreach (MethodInfo method in sDRMethods)
{
if (method.Name.Contains(_domainTable))
{
Items = method.Invoke(repositoryObject, null);
break;
}
}
//View uses this Items property of the Model to populate the grid.
public object Items;
//_domainTable is the name of the table/class (in string format).
//repositoryObject is the object that has methods to return IEnumerable<class> collection object of each type.
The problem I have is that I do not know how to cast the "Items" property in my view to iterate through it and build a grid.
I have tried using the "http://mvcsharp.wordpress.com/2010/02/11/building-a-data-grid-in-asp-net-mvc/" but the generic extension method is expecting to know the specific type that it should work with.
I would prefer to use MVC but it looks like I cannot easily have this working(which is very hard to believe).
I really don't like the sound of what you are trying to do. Why convert the table to a string?
The only time you would convert to a string, is when the view gets rendered. And that, in most cases, should be left to the MVC framework.
The code you mentioned uses an HtmlTextWriter which is fine, because it will render straight to the response.
However, it sounds as if you are trying to reinvent the wheel by rendering everything to a string, rather than leaving that to the framework.
Note that in MVC the views are just templates for rendering strings, which is, if I have understood you, exactly what you need.
So, if I have remotely understood what you are trying to do, and it is a big if because your post is not clear, you should pass your class to view as part of the strongly typed model, and then write some basic design logic into the view.
If I am right, which is not certain, I think you have misunderstood how MVC works.
Have a look at a few examples of how to use views to render the data in a model. The model can be any class, it can be an IEnumerable, a list, whatever, and you can use foreach loops in the view to render out what you want, how you want it.
In this sense, MVC is very different to writing custom controls in plain vanilla ASP.NET.
Thanks for your reply awrigley.
The requirement is quite simple. I perhaps made it sound awfully complex in my post.
On an Index view, I have to populate a dropdownlist with all the tables of the application that are system lookup. The "Admin" of the app, selects an item from the dropdownlist which should show the contects of that table in a grid so that the admin can perform CRUD operations using that grid.
What I am trying to do is, pass the selected item (which is the name of the table) to the controller which in turn passes it to the ViewModel class. This class uses reflection to invoke (code shown in my original question) the right method of a repository which has got methods like:
public IEnumerable GetAllTable1Data()
{
.....
}
The problem I have is that when I invoke the method, it returns a type "object" which I cannot cast to anything specific because I don't know the specific type that it should be cast to. When this object is passed to the view, the grid is expecting an IEnumerable or IEnumerable but I do not know this information. I am not able to do this:
(IEnumerable)method.Invoke(repositoryObject, null)
I get: cannot cast IEnumerable to IEnumerable
I (kind of) have the grid now displaying but I am using a Switch statement in the view that goes:
Switch(SLU_Type)
{
case "SLU_Table1": Html.Grid((IEnumerable)Model.Items);
case "SLU_Table2": Html.Grid((IEnumerable)Model.Items);
.....
}
I don't like this at all, it feels wrong but I just cannot find a decent way!
I could have partial views for each of the system look up tables but for that I'll have to add around 30 partial views with almost exactly same code for the Action & View. This does not seem right either!
Hopefully, this gives you a better understanding of what I'm trying to achieve.
Sorry for the newbie question, but I have the following query that groups parking spaces by their garage, but I can't figure out how to iterate the data in the view. I guess I should strongly type the view but am a newbie and having lots of problems figuring this out. Any help would be appreciated.
Public Function FindAllSpaces() Implements ISpaceRepository.FindAllSpaces
Dim query = _
From s In db.spaces _
Order By s.name Ascending _
Group By s.garageid Into spaces = Group _
Order By garageid Ascending
Return query
End Function
The controller is taking the query object as is and putting it into the viewdata.model and as stated the view is not currently strongly typed as I haven't been able to figure out how to do this. I have run the query successfully in linqpad.
Simply have your ViewPage inherit from the generic ViewPage<T> where the T is IEnumerable<Space> (or whatever your model is).
<%#Page ... Inherits="System.Web.Mvc.ViewPage<IEnumerable<Space>> ... %>
If you wish to strongly type the view then the results of your FindAllSpaces needs to be put into an object which is then returned to your view.
So you may have an object called Spaces and it has a property of say type IQueryable and called Spaces.
Then in your view you can itterate through Model.Spaces like foreach(var space in Model.Spaces)
What might be better is that each record that is returned from your query is an object in its own right called Space.
So now your object Spaces has a property called public IQueryable<Space> Spaces {get;set;}
Now in your view you would inherit from <IQueryable<Spaces>> and you can now itterate like this foreach(Space in Model.Spaces).
The final step is to turn each "Space" into a PartialView which inherits from <Space>.
I am new to ASP.NET MVC, particularly ajax operations. I have a form with a jquery dialog for adding items to a drop-down list. This posts to the controller action.
If nothing (ie void method) is returned from the Controller Action the page returns having updated the database, but obviously there no chnage to the form. What would be the best practice in updating the drop down list with the added id/value and selecting the item.
I think my options are:
1) Construct and return the html manually that makes up the new <select> tag
[this would be easy enough and work, but seems like I am missing something]
2) Use some kind of "helper" to construct the new html
[This seems to make sense]
3) Only return the id/value and add this to the list and select the item
[This seems like an overkill considering the item needs to be placed in the correct order etc]
4) Use some kind of Partial View
[Does this mean creating additional forms within ascx controls? not sure how this would effect submitting the main form its on? Also unless this is reusable by passing in parameters(not sure how thats done) maybe 2 is the option?]
UPDATE:
Having looked around a bit, it seems that generating html withing the controller is not a good idea. I have seen other posts that render partialviews to strings which I guess is what I need and separates concerns (since the html bits are in the ascx). Any comments on whether that is good practice.
look at the ContentResult you can specify the mime type of what you return (text/html)
You could alternatively make a control that take a IEnumerable of whatever you put in the selectlist, and build it using the view engine. That way you keep the formatting of the html (in this case a list of options) into a view, and not in your code.
<%# Control Language="C#"Inherits="System.Web.Mvc.ViewUserControl<IEnumerable<Article>>"%>
<%foreach (var article in Model){%>
<option><%:article.Title %></option>
<%} %>
I think I would go for that second one
From what I understood, the jQuery dialog contains a form that, when submitted, will post to an action which updates the database with some information. You want to get the newly added database information and update the same form that was used to trigger the database update.
If that is the case, then I think the best clean and logical option is to return JSON serialization of the items to be put in the drop down right after you update the database. Then, using jQuery, you would clear the drop down and append option tags into it.
You can also write a new, seperate action that returns the JSON serialization of the database objects you need. You would have jQuery call another post to this action as a callback to your first ajax post (the one used to update the database).
Here is a quick snippet
public ActionResult UpdateDatabase(string something)
{
/// update the database
IEnumerable<Items> items = getItemsFromDatabase(); // or w/e
var vals = items.Select(x=> new { value = x.ID, text = x.Name }); // something similar
return Json(vals);
}
Personally, I would write a separate function that returns JSON. This ensure separation of concerns, and gives me a function I can use in many different places.
Returning a JsonResult with all the items is the most versatile and least-bandwidth intensive solution as long as you are happy to iterate through the list in jQuery and update your drop-down list.
Using a partial view is nice for HTML that you can .load(...) directly into your select, but less versatile.
I would go with the JsonResult.
In your Controller:
public JsonResult UpdateItem(string sItem)
{
// 1. Insert new item into database if not exist...
// {update code here}
// 2. retrieve items from database:
IEnumerable<Item> Items = GetItems();
// 3. return enumerable list in JSON format:
return new JsonResult{ Data = new {Items = Items, Result = "OK" }};
}
On client-side:
Iterate through Items array and add the items to your list.
I'm using NerdDinner as a guide for my first MVC/LINQ to SQL project. It discusses the use of the ViewModel pattern when a View needs data from multiple sources - in their example: Dinners and Countries (serves as the drop down list).
In my application, the problem is a bit different. It's not so much different data, rather data linked via a key constraint. I have a Story table that links to aspnet_users via the UserId key. I would like to have easy access to the UserName for each story.
Since I'm using the repository pattern and returning IQueryable in some cases for deferred execution, I'm struggling with the correct way to shape the data. So I'm using this VideModel pattern right now to make it work but not sure if it's the right way.
Instead of returing IQueryable Story (which wouldn't work since I need the UserName), I'm returning a new custom class UserStory, which has a Story property and a string Username property.
What are your thoughts?
It seems like your question has less to do with MVC as it is simply a question about how to access the story data based on the username string.
Would it be possible to create a view in your database with all the UserStory data, the username, along with userid in it? That way, you could select from the view based on the username you have.
To create the view, you would simply have to do a join between the user table and the userstory table based on the userid.
After that, you could still use the repository pattern with the IQueryable being returned.
If you are wanting to do updates, it would be simple to do since you still have the userid, and would be able to link back to the actual table which would need the update.
If you look at Kigg, you will see that they mess about with the initial model to create custom ViewModels. That's the thing that NerdDinner doesn't cover in any detail. You could create a StoriesWithUserName class that inherits from Stories, but adds a new property - UserName. Then you return that to your View which would inherit from IEnumerable<StoriesWithUserName>
[EDIT]
Oops. Didn't spot that you already did this :o)
Using the repository pattern and returning an IQueryable of Stories is fine. The relationship allows you to access the the username value something like this >>
Assuming you are returning the IQueryable in your model object:
foreach(Story story in Model.Stories)
{
// do something with the value
response.write(story.aspnet_user.UserName);
};
Your Repository method would look like this:
public List<Stories> GetStories(Guid UserId)
{
return datacontext.Stories.Where(u => u.UserId = UserId).ToList();
}
The relationship will automatically provide you with access to the UserName value in the foreach loop i first mentioned. nothing more is required.
I'm not sure why your pagination control failed on Count() though??
Hope this helps