This is a hard question to ask without some background on what I am trying to do. I am working on an existing multitenant ASP.NET MVC 3 application (typical forms over data application) but now have to provide the ability for tenants to add custom fields to any page. There is a fixed set of pages that all tenants have but they can add a field anywhere on one of those pages. For example, on a User Profile page which has fields to enter your address a tenant might want to add a County field before the Country field.
The configuration of the custom fields for each tenant are stored in a database which includes information that describes what the field is (textbox, select, etc.) and where it should be rendered such as the route and the id of field it should be inserted before.
Since this is an existing application I have some limitations and wanted to keep all the existing .cshtml Views as the default/base that all tenants have. To get the tenant specific fields added to a page I created a custom VirtualPathProvider that:
Load the standard View defined in the .cshtm file from the standard Views dir
Load the custom field definitions for the view from the database (specific to the tenant making the request)
For each custom field create Razor markup and insert that into the loaded view from step one
Return the combined view that now has both the base and tenant specific code
That design works fine for the first request for a view however, subsequent requests from any tenant just returns the first version. I am pretty sure what is happening here is the ASP.NET runtime is compiling and caching the view so the next request for the view is just coming out of the cache.
So finally the question. How can you override the compilation and caching so you can include something like the id of the tenant so each view is cached once per tenant?
I figured out that you can override the VirtualPathProviders's GetCacheKey method to implement your own key pattern. In my case adding the tenant's key to the end of the cache key like this:
public override string GetCacheKey(string virtualPath)
{
var tenantKey = getTenantKey();
if (VirtualPathHelper.SupportsCustomFields(virtualPath))
{
return string.Join("_", virtualPath, tenantKey);
}
return base.GetCacheKey(virtualPath);
}
In the ASP.NET Temporary Internet files directory the file name for that view would be:
_views_home_index.cshtml_a7c1a66a-ebe4-4ca2-8dc4-7a22b460f368.compiled
Each tenant that requests a view will now get their own version.
Related
Am new to ASP.NET MVC 3.0. Request expert's view on the below mentioned scenario.
I have a customer details page, where only Name is editable. There are 10 other customer properties that are non editable and displayed using SPAN. When user submits the page, I need to update only the Name.
If am using EF, I will have to load customer again, overwrite name and then save. Otherwise I will have to maintain customer model somewhere.
Anyone tried caching model (or viewmodel) using session id? Is it a good practice?
You are almost thinking in right direction.
If am using EF, I will have to load customer again, overwrite name and then save. Otherwise I will have to maintain customer model somewhere.
In Update Method **Load Customer again and update name Only as required and then save
**For 2 reasons
The first and most important rule is 'don't trust user data'. and
Concurrency and to avoid saving old data. See this example
Instead of using Session, I will suggest to use Hidden Field for record LastUpdateDateTime and Customer ID which will be posted back in the model to retrieve record and verify LastUpdatedtime with database record
Tipically, you should use a view model different than the database model. Having said that,in your current case the situation is very simple, submit only the name to the controller and then set the Name property of the object you get from EF with the submitted name.
Caching the view model or the model isn't your concern. The database model caching is handled by EF, your problem is mainly a lack of clear application layering. IN fact I strongly suggest to learn a bit more about the MVC pattern, basic application architecture (2-3 layering) and when and how to use a OR\M (which EF is).
use hidden inputs for other properties in your form. In that way you can get all properties binded to your EF entity and you dont need to get entity again from db.
#Html.DisplayFor(model=>model.x)
#Html.HiddenFor(model=>model.x)
or you can serialize the entity(if you use POCO entities) and set to hidden input. When you post back you should deserialize the entity.
My choice is always first one. :)
I have read Scott Guthrie's Blog - ASP.NET MVC 3: New #model keyword in Razor
One things i don't realizes is a page will binding value in different ways,but why we have to enforce the view binding from Model?
For example, a user control panel of forum website, it may have the user information, the post history, the user setting etc.
From the view of data model, the binding source can be come from different table : users, posts, user_settings etc.
However, one view only can reference one #model directive.
Actually ,i can add what properties to model that i have to use.
So what is the advantage of make the view became strongly-typed?
However, one view only can reference one #model directive.
Yes, and this should be your view model. A view model is a class that you specifically design to meet the requirements of a given view. And you do this for each view
From the view of data model, the binding source can be come from
different table : users, posts, user_settings etc.
Great, then design a view model that will contain all the necessary properties and have the controller build this view model aggregating the information from the different places and pass it to the view for displaying.
You should never pass your domain models to your views. Because views are normally the projection of one or more domain models => thus the need to define a view model.
1) You can use automatic scaffolding
2) IntelliSense support
3) Compile time type checking
Your view model should be decoupled from your business models.
A single page will have a single view model.
For example:
public class UserPost
{
public string UserName { get; set; }
public string Subject { get; set; }
public IEnumerable<Message> Messages { get; set; }
}
Your UserName property will be coming from the Users table and the UserName field in it.
Your Subject might be coming from a Subjects table and the Messages from another one.
Your view should be concerned only with presenting already processed information, and not querying data sources.
Therefore it is best practice to create a ViewModel per View. This ViewModel contains all properties needed by the view (users, post, settings etc).
In the controller/model you can instantiate the ViewModel and fill its properties. So don't supply a single table/list of records to a view, but a ViewModel.
The advantage is that, with everything strongly typed, there's less chance on runtime errors. Further, when something changes (i.e. database columns), these errors will be detected by the IDE directly.
I have quite a complex class that has three one-to-many relationships and two many-to-many relationships with other classes. What I would like to do is to enable the user to fill all the details one by one - in one step or even better in multiple steps (wizard).
My class is called PeriodicTask - user has to select one Server object (which represents SQL Server instance ) and depending on the selection I need to present the user with the ability to select which databases he wants to use ( the best option would be to use checkboxes). I don't really know how to achieve this.
I would start with creating an action that returns JSON with databases for the selected server. It'll be invoked by jQuery. So far so good, but what to do then?
Should I add <input type="checkbox"> to the form for every database or maybe create another form and post to some other action? How to parse that when the form is submitted? Can I split it somehow into smaller steps ? HTTP is stateless so I somehow need to pass or remember the data that was previously submitted - how?
PS> I'm using Entity Framework here, so part of the class hierarchy is as follows:
You could do it like this:
User selects server instance from
dropdownlist.
After selection dropdownlist fires "change "event, handler of
which loads databases list to form using ajax (your action can provide JSON or html with checkboxes)
User selects checkboxes and presses
submit button
On submit you collect
checked item and post to action
using javascript
I would look at creating helpers for each of the options that would be self contained, they could maintain the state themselves.
Another cool option would be to create a tree view, where the root level is your server and next level is database. Load the data into a ViewModel so that it can be used as the data source for a tree view. It seems like a nice interface for what you have.
Believe it or not the Microsoft site is a great place to start when learning MVC
http://www.asp.net/mvc
I am working on a custom Joomla MVC component.
My view has a form where the user enters an ID. I have retrieved the ID ($input_id) in the controller. Now I need to query the database to get the name WHERE ID = $input_id, then write the name to a different database table.
Can this all be done within the controller or do I have to pass my variables to the model somehow? Not sure of the correct way to achieve this within the MVC framework.
All data and data manipulation should be done in the model (e.g. model your data). The controller is there to determine the path of execution and which methods should be called (e.g. the manager aka controller determines what needs to be done).
Have a look at this tutorial which will help you understand MVC for Joomla better by taking you through the development of a simple component.
I know it could be bad to use domain models as view models. If my domain model has a property named IsAdmin and I have a Create controller action to create users, someone could alter my form and get it to POST a IsAdmin=true form value, even if I did not expose such a text field in my view. If I'm using model binding then when I committed my domain model, that person would now be an admin. So the solution becomes exposing just the properties I need in the view model and using a tool like AutoMapper to map the property values of my returning view model object to that of my domain model object. But I read that the bind attribute on a class can be used to instruct the Model Binder which properties it should and shouldn't bind. So what really is the reason for making two separate classes (domain model and view model) that essential represent the same thing and then incure overhead in mapping them? Is it more a code organization issue and if so, how am I benefiting?
EDIT
One of the most important reasons I've come across for a View Model that's separate from the Domain Model is the need to implement the MVVM pattern (based on Martin Fowler's PM pattern) for managing complex UIs.
I have found that while my domain model gets me 85% of the way to having the fields I want, it has never covered 100% of the values I want on my view. Especially when it comes to permissions and whether or not a user should have access to certain portions of the view.
The design concept I attempt to follow is to have as little logic in my views as possible. This means I have fields in my view model like "CanViewThisField" or "CanEditThisField." When I first started with MVC I would have my domain model be my view model and I was always running into the scenario where I needed just one or two more fields to make my view less cluttered. I've since gone the View Model/Model Builder route and it has worked wonderfully for me. I don't battle my code any longer but am able to enhance my view model as I need to without affecting the domain model.
Another good reason to have a ViewModel is paging large sets of data. You could pass the view an array of Person ( Person[] ) but metadata such as the number of pages, the number of the current page, the size of the page would not belong on the Person class.
Therefore a PersonListViewModel would solve this issue.
A ViewModel holds only those members which are required by the View. They can usually be thought of as a simplification or a "flattening" of the underlying domain model.
Think of them like this:
ViewModel: this is the data that is appropriate to render on this
view
Domain model: this is all the information my application needs
about this entity in order to perform all it's functionality
For example, my Order class has a member called Customer which is a composition association, that is, my Order has a Customer. This Customer object has members such as Firstname, Lastname, etc... But how would I show this on a "details" view of the order or a list of Orders and the Customers who placed them?
Well, using a ViewModel I can have an OrderListItemViewModel which has a CustomerName member and I can map the combination of Firstname and Lastname from the Customer object to this. This can be done manually, or much preferably using Automapper or similar.
Using this approach, you can have multiple Order ViewModels that are specific to different views, e.g. the Order list view might render the customer name in a different way to the Order details view.
Another advantage of ViewModels is that you can cut down on extraneous data not required of the underlying domain object on a view, e.g. if I'm viewing a list of orders, do I really want to see all the customer's contact information, billing details, etc...? I guess that depends on the purpose of the list but, probably not.
Sometimes you need to display the data in a specific manner (ie, displaying a date in the format mm/dd/yyyy vs. yyyy/mm/dd) and often it is easier to make this property in the view and not in the domain model, where you would (or should) have a mapping to a column in your db.
you need to remember
that your domain model classes are only used internally; that is, they are never sent to the
client. That’s what your service model types (View Model types) are used for—they represent the data that will be going back and forth between the client and your service.