Entity Framework Core supports composite keys - primary key values generated from two or more fields in the database. However, unlike in previous versions of Entity Framework, you cannot use the Key attribute to define composite keys. Sep 14, 2016 Entity Framework Core supports different key generation strategies like identity, Sequence and HiLo. In my previous post, I talked about using SQL Server Sequence with EF Core to Create Primary Key. Database sequences are cached, scalable and address concurrency issues.
This video and step-by-step walkthrough provide an introduction to Database First development using Entity Framework. Database First allows you to reverse engineer a model from an existing database. The model is stored in an EDMX file (.edmx extension) and can be viewed and edited in the Entity Framework Designer. The classes that you interact with in your application are automatically generated from the EDMX file.
This video provides an introduction to Database First development using Entity Framework. Database First allows you to reverse engineer a model from an existing database. The model is stored in an EDMX file (.edmx extension) and can be viewed and edited in the Entity Framework Designer. The classes that you interact with in your application are automatically generated from the EDMX file.
Presented By: Rowan Miller
Video: WMV MP4 WMV (ZIP)
You will need to have at least Visual Studio 2010 or Visual Studio 2012 installed to complete this walkthrough.
If you are using Visual Studio 2010, you will also need to have NuGet installed.
Typically when you are targeting an existing database it will already be created, but for this walkthrough we need to create a database to access.
The database server that is installed with Visual Studio is different depending on the version of Visual Studio you have installed:
Let's go ahead and generate the database.
Open Visual Studio
View -> Server Explorer Az vm generate new ssh keys.
Right click on Data Connections -> Add Connection…
If you haven’t connected to a database from Server Explorer before you’ll need to select Microsoft SQL Server as the data source
Connect to either LocalDB or SQL Express, depending on which one you have installed, and enter DatabaseFirst.Blogging as the database name
Select OK and you will be asked if you want to create a new database, select Yes
Key generator free download for all softwares. The new database will now appear in Server Explorer, right-click on it and select New Query
Copy the following SQL into the new query, then right-click on the query and select Execute
To keep things simple we’re going to build a basic console application that uses the Database First to perform data access:
We’re going to make use of Entity Framework Designer, which is included as part of Visual Studio, to create our model.
Project -> Add New Item…
Select Data from the left menu and then ADO.NET Entity Data Model
Enter BloggingModel as the name and click OK
This launches the Entity Data Model Wizard
Select Generate from Database and click Next
Select the connection to the database you created in the first section, enter BloggingContext as the name of the connection string and click Next
Click the checkbox next to ‘Tables’ to import all tables and click ‘Finish’
Once the reverse engineer process completes the new model is added to your project and opened up for you to view in the Entity Framework Designer. An App.config file has also been added to your project with the connection details for the database.
If you are working in Visual Studio 2010 there are some additional steps you need to follow to upgrade to the latest version of Entity Framework. Upgrading is important because it gives you access to an improved API surface, that is much easier to use, as well as the latest bug fixes.
First up, we need to get the latest version of Entity Framework from NuGet.
Next, we need to swap our model to generate code that makes use of the DbContext API, which was introduced in later versions of Entity Framework.
Right-click on an empty spot of your model in the EF Designer and select Add Code Generation Item…
Select Online Templates from the left menu and search for DbContext
Select the EF 5.x DbContext Generator for C#, enter BloggingModel as the name and click Add
Now that we have a model it’s time to use it to access some data. The classes we are going to use to access data are being automatically generated for you based on the EDMX file.
This screen shot is from Visual Studio 2012, if you are using Visual Studio 2010 the BloggingModel.tt and BloggingModel.Context.tt files will be directly under your project rather than nested under the EDMX file.
Implement the Main method in Program.cs as shown below. This code creates a new instance of our context and then uses it to insert a new Blog. Then it uses a LINQ query to retrieve all Blogs from the database ordered alphabetically by Title.
You can now run the application and test it out.
Now it’s time to make some changes to our database schema, when we make these changes we also need to update our model to reflect those changes.
The first step is to make some changes to the database schema. We’re going to add a Users table to the schema.
Now that the schema is updated, it’s time to update the model with those changes.
Right-click on an empty spot of your model in the EF Designer and select ‘Update Model from Database…’, this will launch the Update Wizard
On the Add tab of the Update Wizard check the box next to Tables, this indicates that we want to add any new tables from the schema.The Refresh tab shows any existing tables in the model that will be checked for changes during the update. The Delete tabs show any tables that have been removed from the schema and will also be removed from the model as part of the update. The information on these two tabs is automatically detected and is provided for informational purposes only, you cannot change any settings.
Click Finish on the Update Wizard
The model is now updated to include a new User entity that maps to the Users table we added to the database.
In this walkthrough we looked at Database First development, which allowed us to create a model in the EF Designer based on an existing database. We then used that model to read and write some data from the database. Finally, we updated the model to reflect changes we made to the database schema.
In this chapter, let us learn about creating an entity data model with Database First approach.
The Database First Approach provides an alternative to the Code First and Model First approaches to the Entity Data Model. It creates model codes (classes, properties, DbContext etc.) from the database in the project and those classes become the link between the database and controller.
The Database First Approach creates the entity framework from an existing database. We use all other functionalities, such as the model/database sync and the code generation, in the same way we used them in the Model First approach.
Let’s take a simple example. We already have a database which contains 3 tables as shown in the following image.
Step 1 − Let’s create a new console project with DatabaseFirstDemo name.
Step 2 − To create the model, first right-click on your console project in solution explorer and select Add → New Items…
Step 3 − Select ADO.NET Entity Data Model from middle pane and enter name DatabaseFirstModel in the Name field.
Step 4 − Click Add button which will launch the Entity Data Model Wizard dialog.
Step 5 − Select EF Designer from database and click Next button.
Step 6 − Select the existing database and click Next.
Step 7 − Choose Entity Framework 6.x and click Next.
Step 8 − Select all the tables Views and stored procedure you want to include and click Finish.
You will see that Entity model and POCO classes are generated from the database.
Let us now retrieve all the students from the database by writing the following code in program.cs file.
When the above program is executed, you will receive the following output −
When the above program is executed, you will see all the students’ name which were previously entered in the database.
We recommend you to execute the above example in a step-by-step manner for better understanding.
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