I'm trying to implement a more customisable version of using ViewModel attributes and a Model Enricher to populate viewmodels lists like in this this question and associated blog post.
I would like to be able to specify the method on my select list interface from the Attribute.
Each Select List service I have returns an IEnumerable that I use to make a select list and presently exposes an All interface as the sample does. I can easily use the All method because all interfaces provide that. However I often wish to able to use other methods like the AllTradingCompanies() AllManafacturingCompanies() methods of my select list class to get filtered lists.
It is presently looking like I may have to implement a Custom attribute to map to specific e.g. [AllCompanyList] attributes but that moves me away from the nice generic method that the existing version gives me. I guess I could use it to complement it but then its starting to lose some of the charm. I also am implementing IModelEnrichers which can do custom per view model logic.
Any thoughts on a nice way to implement this?
I implemented the solution using pairs of Attributes to define a requirement for data on a ViewModel and a provider of data a repository or a service within my domain. See my follow up question asking whether this is a good idea.
Related
I was going to implement a custom DisplayAttribute in order to allow dynamic display values based on model values, but I can't because DisplayAttribute is sealed.
Before I go off and write my own customer attribute that emulates the behavior of DisplayAttribute, can anybody think of why this is sealed? I'm assuming there is a reason behind it, and if so, that may be the same reason I shouldn't try to "hack" around this limitation by rolling my own.
I'm not asking anyone to read Microsoft's mind, I'm just hoping someone already knows the by-design reason it's sealed, so that I can take that into account when rolling (or avoiding) my own implementation.
In general it is considered best practice to seal attributes. FxCop has a rule about it, defined here. From that page:
The .NET Framework class library provides methods for retrieving custom attributes. By default, these methods search the attribute inheritance hierarchy; for example Attribute.GetCustomAttribute searches for the specified attribute type, or any attribute type that extends the specified attribute type. Sealing the attribute eliminates the search through the inheritance hierarchy, and can improve performance.
Many of the MVC attributes (ActionFilter, etc) are unsealed because they are specifically designed to be extended, but elements in the DataAnnotations namespace are not.
Not exactly what you asked, but following your intent...
You can still allow for dynamic display values, you just wont extend the DisplayAttribute.
Instead, you can implement your own IModelMetadataProvider which could contain any logic needed to create dynamic display values.
Brad Wilson, from the ASP.NET MVC team, has a good article and sample of this on his blog: http://bradwilson.typepad.com/blog/2010/01/why-you-dont-need-modelmetadataattributes.html
I'm working a feature in the application where model will be dynamic in the sense that any settings data could be displayed and the view will get the model based on what tab they clicked on. I use Hidden field to store what the settings name was because they are same as model name. for ex., if tab1-> Settings1 then Model is Settings1[already exists in the Model].So I used # model dynamic in View and used #Html.EditotForModel() to draw the required UI based off the model. My problem is when I do HttpPost on Edit currently I'm using FormCollection to read the data on that page when I declare the model name in the param it will get it for me but I don't know which model is coming back other than by the Hidden variable and I need it because the Model validation is broken because of this issue. Any help or feedback is appreciated? I can give more details if required? Has anybody crossed this issue before??
Dynamics can be a good thing and a bad thing. Using them on models that have a common interface in a controlled manor is best.
There are different options that you can look at:
1)
Have you tried making the action method accept a dynamic type? That might be the easiest way.
You might have to set up a casting helper to cast the object to the correct type based on the hidden field.
2)
I have a similar idea in some code, but I created a viewmetamodel class that contained all my types as nullable properties. My action method accepts this viewmetamodel type and validates the properties that are not null.
In line with this, if your data is not too large, then you could load all the settings tabs and use Jquery apply the tab with on click.
3)
You could also create #sections or use EditorFor(c=>c.settings) for each tab. That way each tab will load a type safe object. You would need to create controllers for each.
I would say pick the easiest method for you. I hope that this at least gives you some ideas.
This is possibly a bit of a stupid question, but I am getting confused due to the ASP.NET MVC book I am currently reading...
Working with Linq-To-SQL it seems to say that it is not good practice to pass the Linq-to-SQL objects straight to the controller, but that each object should be modelled separately first and this should be passed between the controller and the repository.
Say, I have a database of products. Linq-to-SQl creates a product class for me with Name, Price and Whatnotelse properties. I could pass that straight from repository to controller and then view, but instead it seems to recommend that I use and third class, say Product_Entity, with also Name, Price etc. properties and pass that to the controller.
I fail to see the benefit of this approach, except possibly for adding attributes to the properties... But apart from that it seems to have more drawbacks than benefits. Say each product has manufacturer information as well, I don't see how I can model that easily in my third class.
Is this approach really best practice? Or did I misunderstand all that? If so, why is it bad to work straight off the linq-to-sql generated objects? And how do you deal with relationships between objects in y
The huge benefit to this other class you create is that, to use your example, it doesn't necessarily map to either a product or a manufacturer. Think about it like this:
Your Linq to SQL classes are meant for talking in the "data" domain.
Your "data" classes (the ones you're having trouble with) are meant for talking in the "application" domain.
Let's take an example. Suppose in your MVC application you wanted to show a grid of information about products. You want to see their Name, Price (from the Product table) and their Country of Manufacture and Manufacturer name (from the Manufacturer table). What would you name this class? Product_Manufacturer? What if later on you wanted to add properties from yet a third table such as product discounts? Instead of thinking about these objects in purely the data domain, think about them with regard to your application.
So instead of Product_Manufacturer, what about calling it ProductSummaryItem? Each property of the ProductSummaryItem class would map 1:1 with a field shown in your grid on the UI. Your controller would perform the mapping between the information in the data domain (Product, Manufacturer) with the custom class you'd created in the application domain (ProductSummaryItem).
By doing this, you get some awesome benefits:
1) Writing your views becomes really, really simple. All you have to do to display your data is loop through the ProductSummaryItems and wrap them in and tags, and you're done. It also allows for simple aggregation. Say for example you wanted to add a field called ProductsSoldLastYear to your ProductSummaryItem class. You could do that very simply in your views because all it is to them is another property.
2) Since the view is trivial and there's mapping logic in the controller, it becomes much easier to test the controller's output because it's customized to what the view is going to see.
3) Since the ProductSummaryItem class only has the data it needs, your queries can potentially become much faster because they only need to query for the fields that would populate your ProductSummaryItem object, and nothing else. This overhead can become overbearing the more data-domain objects make up your ProductSummaryItem object.
This pattern is called Model View ViewModel (MVVM) and is hugely popular with MVC as well as in frameworks like WPF.
The argument against MVVM is that you have to somewhat reimplement simple classes for CRUD operations. Fair enough, I guess, but you can use a tool like automapper to help out with things like that. I think you'll find fairly quickly, though, that using the MVVM pattern even for CRUD pays dividends, because before you know it, even with simple classes, you'll start wishing you had extra fields which can easily drive your views.
Background
I have a payment page where the user can select from a list of existing payment methods, or specify a new one. The dropdown presents options such as:
Visa - ******1234 (Saved)
Mastercard - ******9876 (Saved)
[New Credit Card ...]
[New Electronic Check ...]
Using jQuery, I toggle hidden DIVs that contain either an informational table (in the case of options 1 or 2 for saved payment methods) or a form (in the case of the [new] options).
I am using a strongly typed class as my view model which contains (among simple types) a CreditCard class and a Check class. Each of these classes uses data annotation validators, as they are used in other parts of the site.
Problem
The problem comes in when the user submits the form. I would like to use model binding to handle the mapping of POST values, but I need the binding and/or validation to fire depending on which option the user selected. For example, if the user selects option 1 or 2 from the list above, I don't want the model validation (or maybe even the binding itself) to fire for the CreditCard or Check objects.
I have researched the possibilities of creating a custom model binder using IModelBinder as well as extending the DefaultModelBinder and just overriding some of the methods. However, I am unsure as to which method is better, and, if extending DefaultModelBinder, which would be the appropriate method to override.
The logic would be fairly simple:
If the user selected one of the existing payment methods, no validation on the CreditCard or Check are required.
If the user selected one of the options to create a new payment method, then only the selected method (CreditCard or Check) needs to be bound and validated
It feels as if extending the DefaultModelBinder is the way to go, as I would like most of the heavy lifting to be done by the framework without the need to create a custom binder from scratch. However, when looking at the available methods to override, it's not clear which is the best one(s):
BindProperty - The problem here is that I basically need to look at one of the properties to determine what other properties should be bound. I don't think I can control the order in which the incoming properties are bound, and I wouldn't want to rely on the order they are set in the HTML form.
OnModelUpdated - By this point, it's too late. The binding validation from the data annotations has been triggered and the ModelState has been updated. I would have to loop through the ModelState and remove the errors that are not relevant.
OnPropertyValidating - At first I thought this is where I should look, but even returning TRUE for all properties (as a test) causes the ModelState to contain binding errors.
I have come across this scenario in other aspects of the application and decided to split up functionality into separate controller/actions to simplify the process. However, I would like to have a better understanding of how to approach more complex UI problems, particularly related to the MVC model binding features.
Any help on this subject would be greatly appreciated.
All the possible values are stored in a dropdown list. Using jQuery, I toggle the form (for a new payment method) and the display (for an existing method)
I have decided to try to circumvent model binding altogether and use FormCollection, IValueProvider, and TryUpdateModel inside my controller action.
Your issue sounds way to specialized to be placed in the default ModelBinder.
The ModelBinder is this seductress that lures you in on the pretense that she can solve all of your problems. But then you start merging ModelState's together and going off to do crazy things with nested objects lists and before you know it she slaps you with divorce papers and takes everything but your bones.
MVC 3 holds some promise to provide a more extensible ModelBinder but from my own personal experience unless its super simple what you need to change, such as empty texboxes becoming "" instead of null, than stay clear away from your own implementation.
The alternative approach is to use the existing ModelBinder functionality piecemeal and using things like Ignore method parameters to clean things up:
if( myModel.IsNewPayment )
UpdateModel( myModel.Payment, "exclude everything else" );
A lot of what your proposing to stuff into the model binder is really business logic too that should be in another layer. I've done some crazy things with my own ModelBinder and now regret every line of code I've written in there. Maybe its just me but your really bending the rules and completely trashing the "single responsibility principal" by putting business and payment logic in there.
My problem is the following and it is related to the change list view of the admin interface.
I have a workorder model with several fields to caracterize the work order.
They are : type, nature, scheduling_type (and others).
When I see the list view, I would like to be able to change the filter (thus be able to create complex ones depending on the values of the different fields of the workorder model - the ones above and dates for example).
I have found post showing how to modify the default queryset (using managers for example) but I can't find a post that will use a value that is given in the url (ex. admin/workorder/planned_corrective). When the parameter planned_corrective is found, it must be used to select the appropriate queryset or manager and render the corresponding list.
As a add on, I want from that list to be able to use the standard admin options (like list filters, search ...) on that query.
Hope it is clear and thanks in advance for your help.
It sounds like you're after a RESTful interface.
You could accomplish much of this just by being clever with your urls.py - ie, defining admin/workoder/planned_corrective and every other possible parameter that could be encoded in the URL.
A lot of this can also be accomplished just by adding a get-absolute-url method to your models.
Or, you could the effort into using something like the django-rest-interface in your app.