I have a MVC3 project that is referencing a WCF web service....and that WCF service references a data class library.
When I try to scaffold a controller, I have the option to select a Model class from a drop-down.
I would expect to see the data classes that are defined in my data class library, but they're are none there. I'm puzzled by this. I thought that because the MVC project is referencing a WCF service that is referencing the data class library that the classes would be available to choose from.
Am I missing something?
I had what sounds like the same problem. Take a look at this answer and verify you don't have the exact same thing happening Attempting to add a strongly typed view does not find any classes in the MVC project
Related
I have a web application with n-tier architecture. All the POCO classes are in a class-library project named EntityFramework and the DBContext class named DB. And another project is WebAPI with all the API controllers. I added the following code in my WebAPI controller:
using EntityFramework;
namespace WebAPI
{
private DB db = new DB();
}
Although I have added the reference of EntityFramework in WebAPI but still the line 'using EntityFramework;' has the red wavy underline and DB object cannot be created.
First of all read what the error message is saying and put it in your Post.
There could be a number of issues that cause that. A couple guesses from me:
You now have 2 dlls called EntityFramework and the code does not know which one you want to reference, hence the error.
the version of the dll does not match where you reference it. So, check both projects and make sure they both target the same framework version.
Do not call your DTO library EntityFramework, chances are you will get issues with the actual EntityFramework dll. Call it DTOs or Models, or anything else.
I am building an ASP.Net MVC 3 web application using Entity Framework 4.1 with the Database First Approach.
I have just setup my solution with separate projects for the following:
UI - MVC app
Model - Class Library
POCOs - Class Library
Repositories - Class Library
Services - Class Library
I have set this up a few times before without any trouble, but now when I try to create a controller in my MVC app, I get the following error:
Unable to retrieve metadata for 'Entityname'. An item with the same key has already been added.
This happens when I try to add any controller with an Entity for its Model class. I am stumped with this. I tried re-creating the model from the db and regenerated my POCO classes, but still this problem exists.
Can anyone please help?
Thanks.
I solved it. When Entity Framework created my entity data model, some of the names it gave to the navigation properties were a bit meaningless. I therefore edited a couple of these properties, however, I ended up naming two different navigation properties, with the same type of association, the same name. Needless to say EF didn't like this. I renamed the offending navigation property. It was a tough one to fix as there were no compile errors from the model.
I will start to code a new Web application soon. The application will be built using ASP.Net MVC 3 and Entity Framework 4.1 (Database First approach). Instead of using the default EntityObject classes, I will create POCO classes using the ADO.NET POCO Entity Generator.
When I create POCOs using this tool, it automatically adds the Virtual keyword to all properties for change tracking and navigation properties for lazy loading.
I have however read and seen from demonstrations, that Julie Lerman (EF Guru!) seems to turn off lazy loading and also modifies her POCO template so that the Virtual keyword is removed from her POCO classes. Julie states the reason why she does this is because she is writing applications for WCF services and using the Virtual keyword with this causes a Serialization issue. She says, as an object is getting serialized, the serializer is touching the navigation properties which then triggers lazy loading, and before you know it you are pulling the whole database across the wire.
I think Julie was perhaps exagarating when she said this could pull the whole database across the wire, however, even so, this thought scares me!
My question is (finally), should I also remove the Virtual keyword from my POCO classes for my MVC application and use DectectChanges for my change tracking and Eager Loading to request navigation properties.
Your help with this would be greatly appreciated.
Thanks as ever.
Serialization can indeed trigger lazy loading because the getter of the navigation property doesn't have a way to detect if the caller is the serializer or user code.
This is not the only issue: whether you have virtual navigation properties or all properties as virtual EF will create a proxy type at runtime for your entities, therefore entity instances the serializer will have to deal with at runtime will typically be of a type different from the one you defined.
Julie's recommendations are the simplest and most reasonable way to deal with the issues, but if you still want to work with the capabilities of proxies most of the time and only sometimes serialize them with WCF, there are other workarounds available:
You can use a DataContractResolver to map the proxy types to be serialized as the original types
You can also turn off lazy loading only when you are about to serialize a graph
More details are contained in this blog post: http://blogs.msdn.com/b/adonet/archive/2010/01/05/poco-proxies-part-2-serializing-poco-proxies.aspx
Besides this, my recommendation would be that you use the DbContext template and not the POCO template. DbContext is the new API we released as part of EF 4.1 with the goal of providing greater productivity. It has several advantages like the fact that it will automatically perform DetectChanges so that you won't need in general to care about calling the method yourself. Also the POCO entities we generate for DbContext are simpler than the ones that we generate with the POCO templates. You should be able to find lots of MVC exampels using DbContext.
Well it depends on your need, if you are going to serialize your POCO classes than yes you should remove them (For example: when using WCF services or basically anything that will serialize your entire object). But if you are just building a web app that needs to access your classes than I would leave them in your classes as you control the objects that you will access in your classes through your code.
When I add a strongly typed view I see my Entities listed in the Model class dropdown. But, if I select an entity and Scaffold, say List, I get a runtime error of object reference not set to an instance of an object.
In past projects I created a Service layer that called LINQ using CRUD. Then I consumed this service in my Controller and manually created the Views from the resulting service classes. It would be a lot easier if MVC just did all that for me.
Is it possible to directly create scaffold views from concrete classes inheriting EntityObject?
Simple answer : Yes.
I just tried the following test case...
New Project
Create EDMX
Build
Add Controller (With Read/Write actions and views using entity framework
pick Model class and context (the thing normally suffixed with 'entities'
click add
run - it works
EDIT: added MVC Scaffolding too...
open package manager
Install-Package MvcScaffolding
Add Controller (MVC Scaffolding controller With read/write actions & views using EF COde)
Build and Run : Also works.
I've been using ASP.net MVC for about two years now and I'm still learning the best way to structure an application.
I wanted to throw out these ideas that I've gathered and see if they are "acceptable" ways in the community to design MVC applications.
Here is my basic layout:
DataAccess Project - Contains all repository classes, LINQ-to-SQL data contexts, Filters, and custom business objects for non-MS SQL db repositories (that LINQ-to-SQL doesn't create). The repositories typically only have basic CRUD for the object they're managing.
Service Project - Contains service classes that perform business logic. They take orders from the Controllers and tell the repositories what to do.
UI Project - Contains view models and some wrappers around things like the ConfigurationManager (for unit testing).
Main MVC Project - Contains controllers and views, along with javascript and css.
Does this seem like a good way to structure ASP.NET MVC 2 applications? Any other ideas or suggestions?
Are view models used for all output to views and input from views?
I'm leaning down the path of making view models for each business object that needs to display data in the view and making them basic classes with a bunch of properties that are all strings. This makes dealing with the views pretty easy. The service layer then needs to manage mapping properties from the view model to the business object. This is a source of some of my confusion because most of the examples I've seen on MVC/MVC2 do not use a view model unless you need something like a combo box.
If you use MVC 2's new model validation, would you then validate the viewmodel object and not have to worry about putting the validation attributes on the business objects?
How do you unit test this type of validation or should I not unit test that validation messages are returned?
Thanks!
Interesting.
One thing I do differently is that I split off my DataAccess project from my Domain project. The domain project still contains all the interfaces for my repositories but my DataAccess project contains all the concrete implementations of them.
You don't want stuff like DataContext leaking into your domain project. Following the onion architecture your domain shouldn't have any dependencies on external infrastructure... I would consider DataAccess to have that because it's directly tied to a database.
Splitting them off means that my domain doesn't have a dependency on any ORM or database, so I can swap them out easily if need be.
Cheers,
Charles
Ps. What does your project dependency look like? I've been wondering where to put my ViewModels. Maybe a separate UI project is a good idea, but I'm not entirely sure how that would work. How do they flow through the different project tiers of your application?