This may seem like a silly question, but I thought I'd ask it anyway :)
When you use Entity Framework's Database First approach you can create an Entity Data Model to describe the structure of your business objects.
You can also use the ADO.Net DbContext Generator to create persistance ignorance POCO classes. However, when you make a change to the Data Model, ie add a new property to an existing Entity, in order for the corresponding POCO class to also reflect this change, do you have to:
Manually add the new property to the POCO class
Recreate all the POCOs again using the DbContext Generator
I guess what I am asking is there anyway the POCO can be automatically updated if a change is made to the Model?
Thanks everyone.
If you're using the T4 Templates that look at the edmx file, you can just regenerate the pocos by running the templates: Click the Transform Templates icon in the Solution Explorer?
)or have I missed something)
Related
Before I used EF4 to generate my entity data model from an existing database. I can do CRUD operations on every generated entity, because the entities context class with all the methods is automatically generated. Now I have upgraded my project to EF6, deleted the files created by the EF4 data model wizard and generated it again using EF6 data model wizard. Now I get a T4 template file with a context class below it, a T4 template file with for every entity a class with code, a empty designer file and an edmx diagram file. But there are no methods such as AddObject, DeleteObject, SaveChanges generated. How can they be generated as it did before with EF4?
EF6 should still generate a context for you. It provides the mentioned methods. Are you sure you just missed in amongs all the .tt files?
EDIT: Also, make sure you have all the proper references to EF. There might be a compiler warning indicating a problem.
I want to hand-write my POCO's as simple classes with virtual properties so that the entity framework can generate proxies. I will enable proxy creation (which is on by default) so I can have change tracking and lazy loading.
My question is: can I have them?
More specifically, I noticed that the POCO template generator generates classes with a FixupCollection<T>. Is that necessary to have? If I make the navigational properties in my simple hand-written POCO a virtual IEnumerable<T>, will that suffice without any FixupCollection<T> stuff?
As an alternative, I could use the POCO template generator but I do not wish to, because my model is quite large and complicated. I will need to keep making changes to the model and will need to keep editing the model class definitions. If I use the POCO template generator, every time I need to regenerate the model for some reason, it will overwrite all my custom changes.
So, is it possible to just have POCO's in the real spirit of their name?
Yes, of corse it is possible.
http://msdn.microsoft.com/en-us/library/vstudio/dd456853%28v=vs.100%29.aspx
FixupCollection class can be used by the POCO classes to keep the opposite ends of a relationships in sync.
http://blogs.msdn.com/b/adonet/archive/2010/01/25/walkthrough-poco-template-for-the-entity-framework.aspx
I was not able to find the answer to this online - please link me if I've overlooked any resources.
I understand how Entity Framework's codefirst works. The question is: how does EF know which model class to create a table for and which model class to just treat as a class?
For example, in the sample MVC4 application that comes from creating a new MVC project with VS 2012 Express Developer, there are classes (LocalPasswordModel, LoginModel, RegisterModel, etc) in the Account Model that have no tables, and EF knows not to generate tables for these classes.
How does EF know this?
Entity Framework looks at your DbContext class, and creates a table for each DbSet<T> property that you define.
EF won't even see any class which is not referenced by the DbContext.
Okay, I feel a bit foolish for having to ask this but I guess my understanding of the inner workings of Entity Framework is lacking.
I'd like to experiment with work with DbContext. I have an existing ASP.NET MVC application using EF 4.2. I can get my entities using:
var context = new MyEntities();
And this works just fine.
But how the heck to I get the same data represented by a DbContext?
So I guess you are using default code generator provided by EDMX designer - it will use ObjectContext and heavy weight EntityObject based entities.
If you want to use DbContext you must:
Turn off that default code generation - in property window remove Custom Tool for EDMX file
Download and install DbContext T4 generator (you can get it directly from extension manager in Visual Studio)
In EF designer select Add Code Generation Item from context menu in the designer surface (not on entity)
Now EF will add two .tt files to your project - one will be responsible for creating a new class for every entity or complex type defined in your EDMX file and the second will be responsible for creating class derived from DbContext and exposing sets for all your entity types
I create persistence ignorant classes for an existing DB which is very big and i don't want to create all classes in the beginning i want to create only classes i need and create each class when i need it.
Is there any feature in Entity Framework can do this?
You can build incrementally your EDMX file adding only entities you need to use at the moment. Than you need to define only POCO classes defined in your EDMX file or you can use POCO template which will generate POCO classes for you.