In an effort to further abstract my repository layer I have attempted to follow the code-first approach as described here: http://msdn.microsoft.com/en-us/magazine/ee236639.aspx.
I have a many-to-many relationship between Account and Subscription entities. A Navigation property exists on each entity pointing to the other (e.g. Account.Subscriptions).
Before I created my own model I was using the Entity generated model and the below worked fine ("db" is the entity context) :
public IQueryable<Account> GetBySubscriptionId(int subId)
{
return from a in db.Accounts
where a.Subscriptions.Any(s => s.SubscriptionId == subId)
select a;
}
Now the model for Account looks like this:
public class Account
{
public int AccountId { get; set; }
public string Name { get; set; }
// nav properties
public virtual List<Subscription> Subscriptions { get; set; }
}
And when I try to run the same LINQ query now I get this error:
"The specified type member
'Subscriptions' is not supported in
LINQ to Entities. Only initializers,
entity members, and entity navigation
properties are supported."
Any suggestions greatly appreciated.
Try changing the signature from
// nav properties
public virtual List<Subscription> Subscriptions { get; set; }
to
// nav properties
public virtual ICollection<Subscription> Subscriptions { get; set; }
Shamelessly nicked from Scott Hanselmann's demo here - http://www.hanselman.com/blog/SimpleCodeFirstWithEntityFramework4MagicUnicornFeatureCTP4.aspx which uses this pattern, also here's a Scott Guthrie demo using the same idea http://weblogs.asp.net/scottgu/archive/2010/07/23/entity-framework-4-code-first-custom-database-schema-mapping.aspx .
List<T> is a concrete implementation of various interfaces (ICollection, IQueryable, IEnumerable etc), Entity Framework uses proxy objects when it retrieves things from the database, hence the virtual declarations, which use different implementations of these interfaces which is where your error is coming from.
Related
I'm using the SimpleMembership.MVC3 package with my MVC3 application and I want to be able to access users from the table through Entity Framework
In examples for doing this with MVC4, you can simply create a POCO to mirror the User table that's been generated, add your DbSet in your DbContext implementation and then query the DbSet like you normally would, ie: context.Users.
This collection is always returning 0 items for me even though there are rows in the table. What am I doing wrong? Here's what I got so far:
[Table("User")]
public class User
{
public int Id { get; set; }
public string UserName { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
public class TestContext : DbContext
{
public DbSet<User> Users { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
base.OnModelCreating(modelBuilder);
}
}
In my service:
model.Accounts = context.Users.ToList();
Thanks!
You do not create your a POCO that mirrors the User table in order to access it directly from EF. There is already a POCO created by the Internet template when you created the project, which you can customize as described here. This same article also shows how you can access the user information by accessing EF directly. You do not create your own context, there is one already in place that you use. Here is a code snippet from that article.
var context = new UsersContext();
var username = User.Identity.Name;
var user = context.UserProfiles.SingleOrDefault(u => u.UserName == username);
var email = user.Email;
The article also has links to download the source code that demonstrates the details on how to do this.
I circumvented the membership classes entirely and implemented a pure EF membership system. I leveraged the System.Web.Helpers Crypto helpers to handle password hashing and just create the AuthCookie when needed.
When creating a new ASP.NET MVC3 application, in the default project there is a Models folder. This Models folder includes the AccountModels - RegisterModel, LoginModel, etc.
I have a separate project for the DAL - it includes a repository and a service.
Now, I have a method in my service:
TblUser Register(RegisterModel model);
For this to work, I must reference the web project in my data project.
Is this appropriate, or should I include my Models folder in my data project instead?
Your first option is not appropriate. That's what's referred to as a circular dependency and it is bad.
Your second option is better, but still not great. Your model classes will undoubtedly have fields and methods which are applicable to your ui only. Those don't belong in your data layer any more than your data objects belong in your web tier. That's an example of coupling - also known as a poor separation of concerns - and it is also bad.
The best option is to separate out data which is needed by both tiers out into a distinct set of classes (sometimes referred to as dto's - data transfer objects - or poco's - plain old class objects). Those classes can reside in your data project or in a project entirely to themselves depending on your needs. If your service resides in a WCF service, these classes will typically be DataContracts. Then, within your MVC project you should have your models, as they are now, but they should contain references to your POCO's instead of holding any data of their own. So in your specific case you would create a RegistrationInfo class (or whatever you want to call it) in your data project, then add a field of type RegistrationInfo to your model and pass it to your service instead of the entire RegistrationModel.
EDIT: added an example
namespace MyProject.Data.Objects {
public class RegistrationInfo {
[Required]
public string Username { get; set; }
[Required]
public string Password { get; set; }
[Required]
public string Email { get; set; }
}
}
namespace MyProject.Data {
public class MyService {
public TblUser Register(RegistrationInfo info) {
// .. save to the database ..
}
}
}
namespace MyProject.UI.Models {
class RegistrationModel {
public RegistrationInfo Info { get; set; }
/* Fields which the ui needs but the database does not */
public bool ConfirmPassword { get; set; }
public bool AllowFreeEmailAddresses { get; set; }
public void Save() {
new MyProject.Data.MyService().Register(this.Info);
}
public RegistrationModel() {
this.Info = new RegistrationInfo();
}
}
}
I have two database classes as defined below:
public class TopDate
{
[Key]
public int DateId { get; set; }
public DateTime Date { get; set; }
}
public class TopSong
{
[Key]
public int SongId { get; set; }
public string Title { get; set; }
public int DateId { get; set; }
}
where DateId is foreign key to TopSong
I am creating a controller through which i can create, delete or edit these database values.
When i right click on controller class and add controller i can only select one of the two classes defined above. Is there a way to make 1 controller to handle database updates to both these tables on one page?
Error Image:
Your controller should not be dealing directly with domain objects (meaning those things that are directly associated with your database). Create a ViewModel that contains the properties that you need, use your service layer to populate the ViewModel and your controller will use that as the Model for its base. An example of your ViewModel could be something like the following given your description above:
public class MusicViewModel
{
public int SongId {get;set;}
public string Title {get;set;}
public IEnumerable<DateTime> TopDates {get;set;}
}
This view model would contain a list of all dates that a specific song was a Top Song.
The objects you showing (code) are database classes (so called domain objects).
What you need to do is to define a view model, a standard ASP MVC practice:
you define a class, that is tailored for specific view and only containing data relevant to that particular view. So you will have a view model for a view that will create a song, another that will update it etc.
Actually situation you describing is classical situation to use view models. Using domain objects in the views, however, is really really bad practice and prone to more problems than you want to deal with.
Hope this helps.
I am building an application using MVC3, Razor view engine, Repository Pattern with Unit of Work and using EF4.1 Code First to define my data model.
Here is a bit of background (gloss over it if you want).
The application itself is just an Intranet 'Menu'.
The 2 main entities are MenuItem and Department of which:
MenuItem can have many Departments
Departments can have many MenuItems
MenuItem may have a MenuItem as a parent
This is how I have defined my Entities
public class MenuItem
{
public int MenuItemId { get; set; }
public string Name { get; set; }
public string Url { get; set; }
public virtual ICollection<Department> Departments { get; set; }
public int? ParentId { get; set; }
public virtual MenuItem ParentMenuItem { get; set; }
}
public class Department
{
public int DepartmentId { get; set; }
public string Name { get; set; }
public virtual ICollection<MenuItem> MenuItems { get; set; }
}
I am using the FluentAPI to define the Self Reference Many-to-Many for the MenuItem.
The issue I am having is passing a MenuItem to the view via JSON.
The central issues are that I have a circular reference between my entities that the built in JSON parser can't deal with and I have lazy loading and proxy generation still enabled.
I am using JSON.net library from Nuget as my JSON Serializer as this seems to be a nice way round the circular reference issue. I now am unsure how to 'fix' the proxy generation issue. Currently the serializer throws The RelationshipManager object could not be serialized. This type of object cannot be serialized when the RelationshipManager belongs to an entity object that does not implement IEntityWithRelationships.
Can anyone help me with this? If I turn off proxy generation, I am going to have a hell of a time loading all of the MenuItem children so I am keen leave this on. I have read a fair amount and there seems to be a variety of different answers including projecting the entities into another object and serialize that, etc, etc. Ideally there would be some way of configuring JSON.net to ignore the RelationshipManager object?
Update
Here is what I have used as a Custom ContractResolver for JSON.Net serializer. This seems to have sorted out my issue.
public class ContractResolver : DefaultContractResolver
{
private static readonly IEnumerable<Type> Types = GetEntityTypes();
private static IEnumerable<Type> GetEntityTypes()
{
var assembly = Assembly.GetAssembly(typeof (IEntity));
var types = assembly.GetTypes().Where(t => String.Equals(t.Namespace, "Namespace", StringComparison.Ordinal));
return types;
}
protected override List<MemberInfo> GetSerializableMembers(Type objectType)
{
if (!AllowType(objectType))
return new List<MemberInfo>();
var members = base.GetSerializableMembers(objectType);
members.RemoveAll(memberInfo => (IsMemberEntityWrapper(memberInfo)));
return members;
}
private static bool AllowType(Type objectType)
{
return Types.Contains(objectType) || Types.Contains(objectType.BaseType);
}
private static bool IsMemberEntityWrapper(MemberInfo memberInfo)
{
return memberInfo.Name == "_entityWrapper";
}
}
IEntity is an interface all my Code First entity objects implement.
I realise this question has an accepted answer, but I thought I would post my EF Code First solution for future viewers. I was able to get around the error message with the contract resolver below:
class ContractResolver : DefaultContractResolver
{
protected override List<System.Reflection.MemberInfo> GetSerializableMembers(Type objectType)
{
if (objectType.Namespace.StartsWith("System.Data.Entity.Dynamic"))
{
return base.GetSerializableMembers(objectType.BaseType);
}
return base.GetSerializableMembers(objectType);
}
}
This works because EF Code First classes inherit from the POCO class that you actually want serialized, so if we can identify when we are looking at an EF generated class (by checking the namespace) we are able to just serialize using the properties from the base class, and therefore only serialize the POCO properties that we were really after in the first place.
Well, you used powerful serialization API which serializes references and all members as well and now you complains that it serializes all members :)
I didn't test it but I believe this will bring you close to the solution.
JSON.NET is quite powerful tool and it should offer you the extensibility point to avoid this behavior but you will have to code it yourselves. You will need custom DataContractResolver where you define which members should be serialized. Here is the similar example for NHibernate.
You can implement some logic which will take only members present in the parent class of dynamic proxy. I hope this will not break lazy loading. To validate that current entity is proxy you can use this code to get all known proxy types:
IEnumerable<Type> types = ((IObjectContextAdapter)dbContext).ObjectContext.GetKnownProxyTypes();
I'm reading Sanderson's "Pro ASP.NET MVC Framework".
I'm confused a little with decoupling implementation.
He uses LinqToSql in the code sample and repository pattern to interact with database.
[Table(Name = "Products")]
public class Product
{
[Column(IsPrimaryKey = true, IsDbGenerated = true, AutoSync=AutoSync.OnInsert)]
public int ProductID { get; set; }
[Column]
public string Name { get; set; }
[Column]
public string Description { get; set; }
[Column]
public decimal Price { get; set; }
[Column]
public string Category { get; set; }
}
public class SqlProductsRepository : IProductsRepository
{
private Table<Product> productsTable;
public SqlProductsRepository(string connectionString)
{
productsTable = (new DataContext(connectionString)).GetTable<Product>();
}
public IQueryable<Product> Products
{
get { return productsTable; }
}
}
SqlProductsRepository is dataLayer here as it interacts with database.
1.However it is located in DomainModel project. Maybe it is just for demo?
So where is domain logic here?
2.I can't see full decoupling as Products property return IQueryable.
Is it assumed that if we change a component, it must contain Product class?
I seem that it is required to have one more project with abstractions:
Repository Interfaces such as IProductRepository and MappingClasses interfaces such as IProduct.
DataLayer component must implement these abastractions.
Is it right?
Maybe it is diffucult to explain it shortly, however how it is usually work in live projects?
IMHO, this must have been for demo purposes as it doesn't make sense (in real world environments) to separate your architecture in layers and keep these different layers in a single dll. I just came up with a valid reason. What if you want multiple applications to use your business layer without immediate access to the datalayer. You'd have to carefully consider access modifiers to your datalayer but it would be possible.
Whether you should expose IQueryable objects from your datalayer is a discussion that has been going on since the invention of the repository pattern. And there are quite a lot of resources to be found about it.
To list a few:
http://mikehadlow.blogspot.com/2009/01/should-my-repository-expose-iqueryable.html
How can I write a clean Repository without exposing IQueryable to the rest of my application?
To return IQueryable<T> or not return IQueryable<T>
http://www.weirdlover.com/2010/05/11/iqueryable-can-kill-your-dog-steal-your-wife-kill-your-will-to-live-etc/
... (google)