I've got a LINQ to SQL object, and I want to group the selected data and then pass it into a view. What's the correct way of doing this? I'm sure I need to group the data when I select it rather than grouping it in the view, as this will result in about 200 rather 50000 rows I need to pass into my view. Are there any good examples of this online that anyone has seen?
Cheers
MH
-----edit-----
I want a bit of both:-
for example, my data object has (amongst others) 2 properties I want to extract, and group on, ItemDetail.ItemID and ItemDetail.Label - it is a set of those I want to pass into my view. My data factory returns a IQueryable which will contain (in live) about 100 records for each ItemID/Label combination, and thus I want to group this in my view so that it only shows 1 row per ItemID/Label combination.
Also, how do I type my View - I have tried passing in something like the var xxx = ...; return View(xxx); but I'm not sure how to strongly type (if I can) the view properly. I can probably boj this and get it working, but I wanted to do this correctly.
----edit 2----
I've just got a bit further on this.
using the var IQueryable itemDetList
itemDetList = itemDetList.OrderBy(i => i.ItemID).GroupBy(i => i.ItemID).Select(i => i.First());
produces a grouped list, with 1 row per ItemID, and preserves the object typing so that I can pass it into a strongly-typed view - is that the correct way of manipulating the data? How can I put another layer of grouping so that it groups by .Label within each .ItemID group?
You may want to abstract the model you pass to your view from the LINQ 2 SQL objects; check out the View Model Pattern. If this means you find yourself potentially writing lots of code to map properties from LINQ 2 SQL objects to your View Model objects then consider using AutoMapper.
Well, then group the data and pass it onto your View from your Controller...
public ViewResult Foo()
{
var data = this.GetGroupedData();
return this.View(data);
}
private IEnumerable<Bar> GetGroupedData()
{
return from x in GetData()
group x by x.Baz into g
select new Bar(g.Key);
}
I would define Presentation-Models that represent your groups in your View. Fill the Presentation-Models with LINQ and pass them to your View.
With Presentation-Models you have strongly typed data to display in your view.
Related
when do you think is it better to use ViewData over a view model?
I have the same exact partial view in a couple of main views. I'd like to control how a partial view is rendered but I'd also prefer the partial view to accept only a view model which is a collection of records, just a pure IEnumerable<> object. I'd rather avoid to send the full view model object from a main view because it also contains a lot of different properties, objects, that control paging, sorting, filtering etc.
Therefore the question is if I should create another view model for the partial view or is it ok to use ViewData? I've read soemwhere that using ViewData is a very bad practice.
With View Data, I could simply pass require details like this:
#{
ViewDataDictionary vd = new ViewDataDictionary
{
new KeyValuePair<string,object>("WithDelete", Model.WithDelete),
new KeyValuePair<string,object>("WithRadarCode", Model.WithCode)
};
}
// ...
#if (Model != null) {
Html.RenderPartial("_ListOfRecordingsToRender", Model.recordingViewModel, vd);
}
At the moment, it would be sorted out.
My worry is that currently this *.recordingViewModel has plenty of different variations in my project, because of different models for creating / editting, listing, shoing details of a record etc. I feel like it may start to be too messy in my project if I make view model for each action.
What do you think. Please could you advice on that particular problem. Thanks
I think you should stick to using a ViewModel, your ViewModel is the class that defines your requirements for the view.
My reason behind this is that in the long run, it will be a lot more maintainable. When using ViewBag it's a dynamic class so in your views you should be checking if the ViewBag property exists (And can lead to silly mistakes like typo's) e.g.:
if(ViewBag.PropertyName != null)
{
// ViewBag.PropertyName is a different property to ViewBag.propertyName
}
This type of code can make your View's quite messy. If you use a strongly typed model, you should be able to put most of the logic in your controllers and keep the View as clean as possible which is a massive plus in my books.
You also will also end up (if you use ViewBag) attempting to maintain it at some point and struggle. You are removing one great thing about C#, it's a strongly typed language! ViewBag is not strongly typed, you may think you are passing in a List<T> but you could just be passing a string.
One last point, you also will lose out on any intellisense features in Visual Studio.
I feel like it may start to be too messy in my project if I make view model for each action.
Wont it just be as messy in your controllers assigning everything to a ViewBag? If it was a ViewModel you could send it off to a 'Mapping' class to map your DTO to your View.
Instead of this:
// ViewModel
var model = new CustomViewModel()
{
PropertyOne = result.FirstResult,
PropertyTwo = result.SecondResult,
}
//ViewBag
ViewBag.PropertyOne = result.FirstResult;
ViewBag.PropertyTwo = result.SecondResult;
You could do this:
var mapper = new Map();
var model = mapper.MapToViewModel(result);
*You would obviously need to provide an implimentation to the mapping class, look at something like Automapper
I'd also prefer the partial view to accept only a view model which is a collection of records, just a pure IEnumerable<> object. I'd rather avoid to send the full view model object from a main view because it also contains a lot of different properties, objects, that control paging, sorting, filtering etc.
That is fine, just create a view model that has a property of IEnumerable<T>. In my opinion you should try and use a strongly typed ViewModel in all of your scenarios.
I'm using
ViewBag.Something = session.Query<Something>().ToList();
To pass information from class Something to View and use it in selectList
#Html.DropDownListFor(model => model.model, new
SelectList(ViewBag.Something, "Id", "name"), "--Smthing--")
Is that bad? and how can i change it to be better?
The practice is not at all bad but it is recommonded to have a List property in our mode it self. in your case something like
public ActinResult YourActionMethod()
{
YourModelObject.Something = session.Query<Something>().ToList();
// And return your view after further code statements
return View(YourModelObject);
}
Infact instead of the original list object you cancreate a SelectList object where you can easily bind key and value and send it to view. By this way you can add all your business and build your model at once place and can populate it from the location you want to. Later View will just use that model rather than applying some more intelligence to it. It helps alot as all your values resides under same object rather than some in Model and some in ViewBag.
Secondly this practice is also fine if you don't have this list at more than one place and you are not reusing this model in any views. Also if you want to access this property outside your view e.g. in Layout or in some parent view which is consuming your view.
You can take a look at following post which explains how to bind a list to your model.
Setting default selected value of selectlist inside an editor template
I prefer to add all my properties to the model of the view, but the ViewBag can be useful to add things that don't quite fit in the model. It can also be useful when binding to elements in the layout since it doesn't have access to the view's model.
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'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