EF 4.2 Model & Database First Walkthrough

Artikel
09/28/2011

The information in this post is out of date.

Visit msdn.com/data/ef for the latest information on current and past releases of EF.

For Model First see https://msdn.com/data/jj205424

For Database First see https://msdn.com/data/jj206878

This post will provide an introduction to Model First and Database First development with the DbContext API, using the Entity Data Model Designer in Visual Studio.

You will need to have Visual Studio 2010 or Visual Studio 11 installed to complete this walkthrough.

1. Create the Application

To keep things simple we’re going to build up a basic console application that uses the DbContext to perform data access:

Open Visual Studio
File -> New -> Project…
Select “Windows” from the left menu and “Console Application”
Enter “ModelFirstSample” as the name
Select “OK”

2. Create the Model

Let’s go ahead and add an Entity Data Model to our project;

Project –> Add New Item…
Select ‘Data’ from the left menu
Select ‘ADO.NET Entity Data Model’ from the list of available items
Name the model ‘PersonModel.edmx’
Click ‘Add’

We are going to use Model First for this walkthrough but if you are mapping to an existing database you would now select ‘Generate from database’, follow the prompts and then skip to step 4.

Select ‘Empty model’
Click ‘Finish’

Let’s add a Person entity to our model:

On the design surface; Right Click –> Add –> Entity
Name the entity ‘Person’
Click ‘OK’
On the Person entity; Right Click –> Add –> Scalar Property
Name the property ‘Full Name’

3. Create the Database

Now that we’ve defined the model we can generate a database schema to store our data:

On the design surface; Right Click –> Generate Database from Model
Click ‘New Connection…’
Specify the details of the database you wish to create
Click ‘OK’
If prompted to create the database; click ‘Yes’
Click ‘Next’ then ‘Finish’
On the generated script; Right Click –> Execute SQL…
Specify your database server and click ‘Connect’

4. Swap to DbContext Code Generation

The PersonModel is currently generating a derived ObjectContext and entity classes that derive from EntityObject, we want to make use of the simplified DbContext API.

To use DbContext we need to install the EntityFramework NuGet package:

Project –> Add Library Package Reference…
Select the “Online” tab
Select the “EntityFramework” package
Click “Install”

Now we can swap to using DbContext code generation templates:

On the design surface; Right Click –> Add Code Generation Item…
Select ‘Online Templates’ from the left menu
Search for ‘DbContext’
Select ‘EF 4.x DbContext Generator’ from the list
(If you are using EF 5 you should select ‘EF 5.x DbContext Generator’ instead)
Name the item ‘PersonModel.tt’
Click ‘Add’

You’ll notice that two items are added to your project:

PersonModel.tt
This template generates very simple POCO classes for each entity in your model
PersonModel.Context.tt
This template generates a derived DbContext to use for querying and persisting data

5. Read & Write Data

It’s time to access some data, I’m padding out the Main method in Program.cs file as follows;

 class Program 
{ 
  static void Main(string[] args) 
  { 
    using (var db = new PersonModelContainer()) 
    { 
      // Save some data 
      db.People.Add(new Person { FullName = "Bob" }); 
      db.People.Add(new Person { FullName = "Ted" }); 
      db.People.Add(new Person { FullName = "Jane" }); 
      db.SaveChanges();

       // Use LINQ to access data 
      var people = from p in db.People 
        orderby p.FullName 
        select p;

       Console.WriteLine("All People:"); 
      foreach (var person in people) 
      { 
        Console.WriteLine("- {0}", person.FullName); 
      }

       // Change someones name 
      db.People.First().FullName = "Janet"; 
      db.SaveChanges(); 
    }

     Console.WriteLine("Press any key to exit..."); 
    Console.ReadKey(); 
  } 
}

Summary

In this walkthrough we looked at Model First and Database First development using the DbContext API. We looked at building a model, generating a database, swapping to DbContext code generation and then saving and querying data.

Rowan Miller

Program Manager

ADO.NET Entity Framework

Comments

Anonymous
March 13, 2012
Why not include how to remove a row in this tutorial? For me that's the next logical step.
Anonymous
March 13, 2012
Remove an entity: using (var db = new MyEntities()) { var entity = db.EntitySet.Single(b => b.SomeIdentifier == id); db.EntitySet.Remove(entity); db.SaveChanges(); }
Anonymous
March 15, 2012
Sorry, but this does not work. I have followed the step-by-step instructions with one table from an existing database and it does not generate a PersonModelContainer as used in the last step. I have tried EF4.3.1, EF4.3 and EF4.2. Is there something I am missing? Thanks
Anonymous
March 15, 2012
@Tim - The name of the context will depend on what you called the connection string when you reverse engineered from the database. If you right-click on the design surface of your model and select 'Properties...' there will be an Entity Container Name property that will tell you what the context is called (you can also change it if desired).
Anonymous
April 03, 2012
I see no EF 5.x generators yet. You mention them and I was wondering if it's fine to use the 4.x generators?
Anonymous
April 03, 2012
@Tim The EF 5.x DbContext generators are available if you are targeting .NET 4.5 on VS 11. If you are targeting .NET 4 then you should use the 4.x generators for now. Updated 5.x generators that will work with .NET 4, .NET 4.5, VS 2010, and VS 11 will be available soon.
Anonymous
April 09, 2012
Hi, Does ADO.NET Entity Framework support web base DB CRUD generating/operation? Thanks
Anonymous
April 11, 2012
@semetah – Are you asking about exposing CRUD operations over the web? If so then WCF Data Services and Web API are two technologies that work nicely with EF to achieve this.
Anonymous
April 11, 2012
Thanks Rowan, is there a demo site, or tutorial, or documentation for building CRUD operations over the web using WCF Data Services and EF Web API? Thanks
Anonymous
April 11, 2012
@semetah - You can find info about Web API here; http://www.asp.net/web-api. The current preview doesn't automatically scaffold controllers with logic to interact with an EF model but that is coming in their next release. This article & video cover using WCF Data Services with EF; msdn.microsoft.com/.../hh272554.
Anonymous
May 06, 2012
Hello, I think your article misses a 'system requirements' section, I followed exactly the steps described and a DbUpdateException (Server-generated keys and server-generated values are not supported by SQL Server Compact.) occurred, using SQL CE 3.5. For people who are willing to use it, the person Id should be set as well.
Anonymous
May 06, 2012
Sorry I talked too fast ... even when setting an ID, CE 3.5 does not work at all (correct me if that's wrong), 4.0 works but there's a trick. to make it work : stackoverflow.com/.../entity-framework-4-and-sql-compact-4-how-to-generate-database
Anonymous
June 08, 2012

step doesn't work in VS 2011, any idea? None of the DbContext Generator are in the list...

Anonymous
June 10, 2012
@uesendir - Are you looking on the Online tab?
Anonymous
June 12, 2012
Where does the "People" in db.People.Add(new Person { FullName = "Bob" }); come from?? Shouldn't it be called: db.PersonSet.Add(new Person { FullName = "Bob" }); I followed the example, as much as possible (i don't have a Project->Add Library Package Reference... but instead used the Project -> Manage NuGet Packages... (i assume it's the same) to add the EF 4.3.1) I don't have a People class. I used VIsualStudio 2012 & EF 4.3.1
Anonymous
June 12, 2012
Sorry i've obviously NOT used VS 2012 :-) but Visual Studio 2010 Pro
Anonymous
June 13, 2012
@Jan - People isn't a class but rather a property of the context. You actually get to choose the name when you add the entity to the design surface (but by default it will calculate the plural of the name you give the entity).
Anonymous
July 28, 2012
Rowan, are you there? I need some help. I need to learn to set up good unit tests to DbContext using Moq. I followed the steps here: blogs.msdn.com/.../productivity-improvements-for-the-entity-framework.aspx The t4 template generated a DbContext context class. I edited and changed DbSet to IDbSet. I extracted an interface. I added all the public properties and methods from the DbContext class. Then I mock this super interface. This gets me some decent looking code that builds, but it does not run. public partial class PosManContext : DbContext, IPosManContext { public PosManContext() : base("name=PosManContext") { } protected override void OnModelCreating(DbModelBuilder modelBuilder) { throw new UnintentionalCodeFirstException(); } public IDbSet<note_template> note_template { get; set; } } public interface IPosManContext { DbChangeTracker ChangeTracker { get; } DbContextConfiguration Configuration { get; } Database Database { get; } void Dispose(); DbEntityEntry Entry(object entity); DbEntityEntry<TEntity> Entry<TEntity>(TEntity entity) where TEntity : class; bool Equals(object obj); int GetHashCode(); Type GetType(); IEnumerable<DbEntityValidationResult> GetValidationErrors(); int SaveChanges(); DbSet<TEntity> Set<TEntity>() where TEntity : class; DbSet Set(Type entityType); string ToString(); IDbSet<note_template> note_template { get; } } unit test code: Mock<IPosManContext> posManContext; posManContext.Object.Set(typeof(note_template)); posManContext.Object.note_template.Add( new note_template() { note_template_id = 1, act_flag = "Y", desc_text = "Monday Monday", last_update_dtm = now, last_update_user_id = "hsimpson", }); I get an error that the DbSet is null. Microsoft needs to provide a good example of what to do for unit test using mocking. They went half the way by providing public interfaces for mocking, but I still need more help. Joe
Anonymous
July 30, 2012
@Joe Kahl – The note_template property is returning null because you haven’t set it up to return anything in the mocked context, you would need to create a mock of the DbSet and then setup the note_template property to return that mock. Here is some documentation on getting started with Moq - code.google.com/.../QuickStart. If you are still running into issues then please start up a http://stackoverflow.com/ thread and tag it with ‘entity-framework’ and ‘moq’.
Anonymous
August 09, 2012
Found a little bug for the .tt Wizard. (Microsoft.Data.Entity.Design.VisualStudio.ModelWizard.AddArtifactGeneratorWizard) When you add the .emdx file as a link from another project in another solution, the $edmxInputFile$ in the .tt templates gets replaced properly, so with the relative path "...." etc, but when you add the .edmx file as a link from another project in the same solution the $edmxInputFile$ doesn't get a relative path and an exception is thrown. Not sure if one would even need to do this, but it shouldn't crash at least. Thx.
Anonymous
August 10, 2012
This doesn't really showcase any differences with DbContext compared to the default ObjectContext model. I re-created this tutorial following every step except for adding the DbContext package, and the code worked exactly the same except I had to write db.People.AddObject(new Person ...) instead of db.People.Add(new Person ...).
Anonymous
August 15, 2012
@Jorris - I've opened a bug to track this - entityframework.codeplex.com/.../450
Anonymous
August 15, 2012
@Moozhe - The advantages of DbContext really surface when you start using you model to do more than just add a single object. Although it is certainly easier to find the Add and SaveChanges methods on DbContext (ObjectContext will give you 50+ members to sift through in IntelliSense).

Bagikan melalui