I am delving into the EntityFramework 4 code first of entities approach and I am getting stuck on how to take the ObjectContext / Entities and link them to a database.
I have looked at varous sites on [msdn][1] and [blogs][2] about how to use all of this but they all fail in talking about how to create a database that the entities will be saved in or don't take the code first apprach. I know I can create an edmx file and generate sql from that but since I am writing my entities first this file is empty and through the designer I don't see a way of adding my entities without duplicating effort (in creating all the entities/fields etc).
There does not seem to be the EntityConfiguration class in the full release of entity framework. It appears to be only in the CTP that I am NOT using (a lot of the examples on the web use the CTP).
Also the following context takes strings that in no way seem to relate to the edmx or database.
public class EntityContext : ObjectContext
{
public EntityContext()
: base("name=ExampleEntities", "ExampleEntities")
{
ContextOptions.LazyLoadingEnabled = true;
Users = CreateObjectSet<User>();
}
public IObjectSet<User> Users { get; set; }
}
So the question is.
How do I create a database schema that maps to my entities?
Should I use an edmx file at all or create my own database file (.mdf)?
If I do use the edmx file how do I add my code first entities easily?
How do the ObjectSets within the ObjectContext map to the database?
Thanks
EDIT
I am using VS2010 professional and the classes that come with that. I see CTP4 is out so I assume the RTM version is not out yet. Is this correct?
Add this to your application_start event to create the database:
Database.SetInitializer<YourObjectContextClass>(new RecreateDatabaseIfModelChanges<YourObjectContextClass>());
Looks like I needed CTP4 found here
I also followed the walkthrough
Related
I am developing a web-based system using .NET MVC and Entity Framework, from a legacy system. I will keep the legacy database and only develop the application, so I will create entity classes using database first approach.
My concern is, in the entity classes, I will be adding attributes such as filter attributes. And I may add some extra fields there as well. Will the database be updated automatically? I actually don't want to update the database at all. I only want extra stuff stay with the entity class only.
You can easily create your database first and then start working on the backend side of your application as you would do it in an "Code first" approach.
I'd recommend reading this article, as you might get all your answers cleared with some examples: Entity framework
First, when adding additional properties in your entity classes you will want to mark them for EF to ignore using either the [NotMapped] attribute or in your DbContext class calling .Ignore on the property. Not Mapped Attribute
Second, in terms of EF changing your database you can do a couple of things.
1. Ensure the account that is updating data does not have Create,Alter,etc permissions in the environment
2. Use a null database initializer at the beginning of your application. Database.SetInitializer(null); Setting the initializer to null tells EF not to make any sort of changes to the database. Turn off DB Initializer
Maybe you should consider using partial classes.
I find editing anything in EF quite hard.
EF Classes from your DB are all :
public partial myClass(){
public string myDBProperty;
}
Which means you are able to create a second class in the same namespace like :
public partial myClass(){
public string myOwnProperty;
}
Using the wizard, I created a DbContext from an existing database and only selected one table to be pulled in. However now I need to add additional tables from that database to the Entity Model.
What is the easiest way to add more tables from an existing database to a context that I have already created and to also generate the respective models for those tables?
Easiest way is:
1) Open your .edmx database
2) Right click and choose "Update model from database..."
3) check the tables you want and click finish
4) EF will create all your entity classes for you
If you want to add the tables manually to your DbContext, you can do so by adding properties of type DbSet to the DbContext. For ex:
public DbSet<CarColor> CarColors { get; set; }
I think EntityFramework Reverse Poco Generator is what you're searching for.
It's an extension for VS which allows to populate a TT file, then creating POCO entities for you.
It is downloadable here: EntityFramework Reverse Poco Generator
I've wrote a very brief guide you could refer to, in order to setupt the extension and use it for your means. Check it here: Introduction to EntityFramework Reverse POCO Generator for Visual Studio
I tried finding the answer to this question before posting, but couldn't.
We are using a remote database with Entity Framework and I do not know the approach it was used to create the database. What I would like to do is add a class to the project, add the class to DbSet an create the table automatically. Now, when I use update-database in nuget, i get "migrations not enabled for this database" and its true, there is no configuration file or anything that suggest the approach it was used for creation of this.
I wouldn't want to enable-migrations as I don't want to mess something up or loss data. (or should i?) The existing tables are working fine with the repository...
I created a table manually, added a class that maps the properties by name and hoped that entity framework will pick it up, but no luck.
Here it is in a nutshell: I want to add a new table in a remote database that will be picked up by Entity Framework an generate a class for me. There is also NO .edmx file that can update the model. How was this done then... (?)
I am a new to Entity Framework, so apologies it some of this does not make sense. I am happy to clarify.
Thanks,
Thank you for your responses. I managed to fix this by adding a new class into the repository, using code first approach and then I created a table manually in the database.. The Entity Framework pick it up somehow :)
I was doing this before, but the problem was that I had the DbSet name to plural and database to singular. For instance: Products was the DbSet name and Product table in database. The actual class is still singular.
Thanks again!
Assumptions
Using EF 6.1, MVC 5, VS 2013, C#
I have an existing database model designed in Toad DM for SQL Server and it's very important keep it always updated
Steps and Notes
Using ADO.NET Entity Data Model I chose Code First from Database (new feature in EF 6.1) to generate the models. Note: Model classes and DbContext class generated successfuly but NO .edmx or .tt file was generated.
Next I added a new scaffold item: MVC 5 Controllers with views, using Entity Framework. Note: Success, controllers and views generated
Question
From now on I don't want to use Code First to update my database. Instead I want the models to be updated based on database changes. What to do next? If I don't have an edmx file will I not be able to update my model classes from the database?
The Entity Data Model Wizard's Code First from Database does an excellent job creating your entity classes, as if they were created in the Code First style. What you are asking is if there is any way to keep these classes up-to-date as your database changes, similar to the EDMX style "Update Model From Database". From what I've researched this is not possible using the built-in tooling. However, here is one workaround that I've found useful:
Let's say I have database with a product table and customer table. Originally I created a StoreDBContext class, and selected product as one of my objects. Now I want to add the customer table as a new entity to the existing context. Here's how to do this using the Code First Wizard:
Create a new Entity Data Model, call it StoreDBContextTemp or whatever
Choose the code first from database wizard option
Select customer as an object to add (just customer) & complete the wizard
Open the newly created context file, StoreDBContextTemp.cs, and copy the virtual properties of your newly added entities:
public virtual DbSet<Customer> Customers {get; set;}
Paste these new properties into your Original StoreDBContext.cs dbcontext class.
Delete StoreDBContextTemp.cs, and remove the connection string for StoreDBContextTemp in app.config/web.confg etc.
You can now use Customer on the StoreDBContext class
If you add or remove tables you will need to manually adjust fields, but at least you won't need to hand write dozens of properties each time a new table is added to the model.
One more option is just delete the auto generated classes from the project and once again generate them.
While following this approach only thing we need to make sure that is we should give the same name for the data model(class name which inherits from DbContext ) as the previous one.Data model name is highlighted in below snap
Three things.
There's no .edmx when you use Code First.
If you use Code First Migrations you would have to write first the code and after that migrate the changes to database. This helps you to have much more organized you code with no generated code which is an advantage.
There's a plugin in Visual Studio for doing contrary. Entity Framework PowerTools allows you to select the database and map it to objects.
https://visualstudiogallery.msdn.microsoft.com/72a60b14-1581-4b9b-89f2-846072eff19d
The best solution to me is deleting the model and recreate updated one with the same name, keeping in mind two points:
Personal extension methods implemented for the model;
Possible manual relationships between tables added to the model because of not setted up in the phisical db.
My personal solution:
Move all extension methods to another partial class that won't be overrided;
Insert all added properties of an entity to another partial class;
Keep track of all manual relationships in an help file, so you can add them again being sure not to loose anything;
Delete the old model and recreate one new with the same name and update it with the manual relationships of point 3.
I'm new to Entity Framework, and I have an existing database that I'd like to add a few tables to, rather than creating a database from scratch for my new tables. Is this possible with Entity Framework?
I've looked through the following MSDN articles on Code First development, and haven't been able to find the answer to my issue:
Code First Development
Code First Conventions
Code First Fluent API
Code First Data Annotations
I have had the same experience with my asp.net mvc3 project, it's a little different from asp.net but I guess entity framework is the focus here.
create new table in sql server
create corresponding model in your model project
Add the new table object property in DbNameEntities.cs
public DbSet NewTables { get; set; }
In Application_Start() method, comment out the original code first approach
System.Data.Entity.Database.SetInitializer(new SeedSampleData());
replace with this:
System.Data.Entity.Database.SetInitializer<DbNameEntities>(null);
Yes, this is certainly possible.
A decent walk-through is available on Scott Gu's blog