few days ago i read tutorial about GenericRepository and Unit Of Work patterns http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application. I use web forms and i have EntityFramework CTP4 package installed. (I can't using EF 5).
I want to code generic repository for my project but i was stuck at this line:
this.dbSet = context.Set<TEntity>();
I know that this line doesn't work because a use ObjectContext in my project and database first approach. How can i deal with it? Can I code generic repository without migration to code first (which is not an option in my case) ?
This is the equivalent for ObjectContext:
this.dbSet = context.CreateObjectSet<TEntity>();
Now this creates an ObjectSet<TEntity> rather than a DbSet<TEntity>, but for your pattern you can use it in the same way.
UPDATE
The ObjectSet class does not have a utility method like that matches the Find() method of the DbSet. In order to "Get by key" you would need to construct an EntityKey and use the ObjectContext.GetEntityByKey(), unfortunately that's not a really simple thing to do.
There really isn't a simple way to tackle this, that I've found. In my case what I've done is to base all of my entities from a common class (using custom T4 templates to generate the classes from the model). And then I can add a generic constraint to my repositories, like:
public class MyRepository<TEntity> where TEntity : MyEntityBaseClass
And then my common base class has an Id field which is inherited by all the entities so I can can simply do:
return myObjectSet.SingleOrDefault(x => x.Id == myId);
I'm sure there are other approaches, that might be a good topic for another question.
1. You want to add the DbContextGenerator template to your visual studio templates:
2. After this make sure you clear out the default generation tool on your .edmx file.
3. Now you can implement the GenericRepository pattern as you wish.
Related
I'm quite new to Entity Framework, but the more I worked with it, the more I actually liked it. But now my passion is at risk, as I'm struggeling with an issue that already made me crush my head against the wall.
The problem is the following:
I'm using Entity Framework 5.0 with code-first approach plus inheritance for my business models represented by Table Per Hierarchy. At first I had all of my entity types, that were supposed to be mapped, in the same assembly as my DbContext (which worked fine for both TPH and TPT). But as they also contain logic that is dependent on other assemblies, this turned out as no good approach since it caused circular dependencies because those assemblies also need to have knowledge of the Data Access Layer, which in turn has to have knowledge of the entity types that it is supposed to map).
I solved this issue by introducing a CommonObjects project, where I now keep all of my abstract classes and stripped out the concrete descendents (containing the logic, etc.) of those base classes into the specific projects, which are responsible for them.
(see: Circular Dependency Solution)
It compiled and everything seemed to fit the way I imagined it.
But now it turned out that Entity Framework seems to struggle with the derivates being in a different assembly than the base classes.
During runtime, when trying to access the DbContext the first time, the compiler threw an InvalidOperationException saying:
The abstract type 'Foo.Bar.AbstractClass' has no mapped descendents
and so cannot be mapped. Either remove 'Foo.Bar.AbstractClass' from
the model or add one or more types deriving from
'Foo.Bar.AbstractClass' to the model.
So EF is obviously not able to find the descendents, as it only knows the base classes (which are in the CommonObjects project), but the descendents are in a different assembly.
DbSet<AbstractClass> AbstractClasses { get; set; }
According to this question:
Entity Framework Code First and Multiple Assemblies
I tried to add the following code to the constructor of my derived DbContext:
((IObjectContextAdapter)this).ObjectContext.MetadataWorkspace.LoadFromAssembly(
Assembly.Load("Foo1"));
But that did not work for me. While debugging and watching the MetadataWorkspace the method "LoadFromAssembly" did obviously not have any effect on the MetadataWorkspace and its items (no types were loaded from assembly Foo1).
What am I missing here?
Thanks for your answers in advance.
Ben
EDIT: This only barely works and isn't worth it, and doesn't work at all if you're using CodeFirst.
I have encountered the same issue with code first. I tried your method of reflection. This seems a bit wonky, but you can trick EF into being okay with your set up with an internal class.
internal class ClassToMakeEFHappy : AbstractClass {}
I just created that in the same file as my AbstractClass definition and it did the trick.
In Entity Framework 5 model first, there seem to be some breaking changes due to the way the class files are generated (No more code generation, but T4 templates)
2 examples:
The generated context file doesn't implement IDisposable anymore
There isn't a constructor which takes a connectionstring anymore
Are there more breaking changes? And what is the solution to them?
The default code generated from a model in Entity Framework 5 now inherits DbContext instead of ObjectContext.
This still implements IDisposable, but if you're getting an error from a line of code similar to this:
using (var mymodel = new MyModelContext()) { ... }
...complaining about not implementing IDisposable, then your problem is most likely that your model is defined in a separate assembly that references EF5 and you have not added an EF5 reference to your project.
As Ladislav Mrnka has already mentioned in his answer, if you want to pass a connection string to the constructor you have to create your own constructor manually to do this.
If you want to switch Entity Framework back to the older style of generated code, which will automatically generate the constructor you're looking for, then follow these steps:
Click on the designer surface of your EDMX file, and look at the properties window. Find a property called "Code Generation Strategy" and set this to "Default" instead of "None". This will tell Visual Studio to start creating the code for your object model in MyModel.Designer.cs in one big file, this time using ObjectContext instead of DbContext.
Delete the following sub files from below your EDMX file: MyModel.Context.tt, MyModel.tt. These are the auto generated files that you don't want anymore. If you don't delete them you'll get class naming conflicts because your objects will be created twice.
The generated context file doesn't implement IDisposable anymore
IDisposable is still implemented by the parent context type. The generated type is still disposable.
There isn't a constructor which takes a connectionstring anymore
It now uses convention to get connection string but you can add your own constructor either to template or to your partial class part of the context.
Are there more breaking changes? And what is the solution to them?
It is whole breaking change because it uses different API - DbContext API instead of ObjectContext API which means different types, different methods, POCO entities etc. If you want to get back to original code generation you have to delete those T4 templates and enable code generation as described in .Designer.cs file but the current recommended way is to use POCOs and DbContext API.
I was having the same issue with the using statement needing a type that extended IDisposable... Turns out that I forgot to reference System.Data.Entity in my project... Added the reference and it fixed the problem.
Just clean and build the project, don't forget to add the reference to your entity.
For various reasons I would like to not store the connection string for my Entity Framework DB model in one of the various .config files. (I am using the latest and greatest DBContext API with the new Entity Framework version 4.1, .NET 4 and Visual Studio 2010 C#.) However, the code generation template for DBContext only creates a single parameterless constructor. (If I don't use the DBContext API, then my entity framework model has 7 different constructors to chose from, including the one I want.)
The only way I could figure out how to do this was to directly modify the code-generation template (context.tt file) to give me the constructor I want (example code below). This works, but it feels like I'm doing it "the hard way". What is the correct way to get a DBContext constructor that accepts a connection string?
public <#=Code.Escape(container)#>(string connectionString)
: base(connectionString)
{
<#
WriteLazyLoadingEnabled(container);
#>
}
One final note in case it might help somebody else. Although this method works, it took me a while to realize that the "connection string" is not strictly the DB connection string, but rather the special entity framework connection string which contains the DB connection string (just like what would be stored in the app.config file).
Your approach looks like the most correct way to do this. It's what the t4 templates were created for, and you're basically doing the same thing that the model-first templates do by default.
Another possibility would be to make the db context class be partial (if it isn't by default) and create another partial class file alongside it to add the constructor you want. But it seems likely that you'll want all of your t4-generated contexts to follow this pattern, so I think it's best to leverage the code generation to do this automatically the way you do in the question.
I have a subclass in a different assembly to its base class. The parent is a POCO class used for EF Code First.
When I try to add an instance of inherited class to the database I get InvalidOperationException: "Object mapping could not be found for Type with identity 'Foo.Bar.MyInheritedClass'".
It works fine if subclass is in same assembly as base class.
In regular EF the solution seems to be a call to ObjectContext.MetadataWorkspace.LoadFromAssembly(assembly). But I can't figure out how this relates to Code First.
Any advice?
I'm using Entity Framework 4.1 RC.
I solved this by inheriting from the first assembliy's DbContext, adding a DbSet<> for the derived class, and then adding new instances of derived type to to that.
Posted code on MSDN forum here.
I know this post is a bit old, but I was able to accomplish this using #Dave's recomendation inside the constructor:
public Context() {
((IObjectContextAdapter)this).ObjectContext.MetadataWorkspace.LoadFromAssembly(
System.Reflection.Assembly.GetAssembly(
typeof(--[Inherited DbContext]--)));
}
I'm quite new to EF (Entity Framework 4) and I got the same exception when I made changes in the model.
My problem turned out to be that I did not know EF need all the names on all the navigation properties to agree, not only their type. For example if there is a navigation property named foo, then there needs to be a declared variable in the corresponding class with the very same name.
HI all
I was trying to follow the POCO Template walkthrough . And now I am having problems using it in n-tiers design.
By following the article, I put my edmx model, and the template generated context.tt in my DAL project, and moved the generated model.tt entity classes to my Business Logic layer (BLL) project.
By doing this, I could use those entities inside my BLL without referencing the DAL, I guess that is the idea of PI; without knowing anything about the data source.
Now, I want to extend the entities (inside the model.tt) to perform some CUD action in the BLL project,so I added a new partial class same name as the one generated from template,
public partial class Company
{
public static IEnumerable<Company> AllCompanies()
{
using(var context = new Entities()){
var q = from p in context.Companies
select p;
return q.ToList();
}
}
}
however visual studio won't let me do that, and I think it was because the context.tt is in the DAL project, and the BLL project could not add a reference to the DAL project as DAL has already reference to the BLL.
So I tried to added this class to the DAL and it compiled, but intelisense won't show up the BLL.Company.AllCompanies() in my web service method from my webservice project which has reference to my BLL project.
What should I do now? I want to add CUD methods to the template generated entities in my BLL project, and call them in my web services from another project.
I have been looking for this answer a few days already, and I really need some guides from here please.
Bryan
Mhhh, your layer architecture looks a bit like a spaghetti plate.
First in my opinion your POCO objects should be put in a different assembly which have no reference to any DAL, or else why bother about POCO ?
Second, static method in partial class don't look good, keep your poco objects very simple, and surrender the logic of it to repositories.
Take a look at that and all will be crystal clear:
http://thedatafarm.com/blog/data-access/agile-entity-framework-4-repository-part-1-model-and-poco-classes/
I don't think DAL should have a reference to BLL. I think it should be vice versa. BLL should be persistence ignorant.