Database Generated Key Entity Framework

11.12.2020
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The BookId property is denoted with DatabaseGeneratedOption.None, so its value must be specified when inserted into the database. When DatabaseGenerated.Identity applied to a property, the entity framework expects the data to be updated by the database when the row is inserted. Entity Framework Key The Key attribute can be applied to a property to make it a key property in an entity class and the corresponding column to a primary key column in the database. The default Code First convention look for a property named 'Id', or a combination of 'class name' and 'Id', such as BookId.

  1. Entity Framework Tutorial Key. The Key attribute can be applied to a property to make it a key property in an entity class and the corresponding column to a primary key column in the database. The default Code First convention look for a property named 'Id', or a combination of 'class name' and 'Id', such as BookId.
  2. Before creating the model, Code First takes convention into consideration first, then reads the data annotation attributes and finally reads the mappings specified by Fluent API. The order of priorities for creating primary key using Entity Framework Code First is: Convention - Data Annotation - Fluent API (Highest Priority).

This video and step-by-step walkthrough provide an introduction to Code First development targeting an existing database. Code First allows you to define your model using C# or VB.Net classes. Optionally additional configuration can be performed using attributes on your classes and properties or by using a fluent API.

Watch the video

This video is now available on Channel 9.

Pre-Requisites

You will need to have Visual Studio 2012 or Visual Studio 2013 installed to complete this walkthrough.

You will also need version 6.1 (or later) of the Entity Framework Tools for Visual Studio installed. See Get Entity Framework for information on installing the latest version of the Entity Framework Tools.

1. Create an Existing Database

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.

Let's go ahead and generate the database.

  • Open Visual Studio

  • View -> Server Explorer/devil-may-cry-steam-key-generator.html.

  • 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 your LocalDB instance, and enter Blogging as the database name

  • Select OK and you will be asked if you want to create a new database, select Yes

  • 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

2. Create the Application

Entity Framework Create Database

To keep things simple we will build a basic console application that uses Code First to do the data access:

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

3. Reverse Engineer Model

We will use the Entity Framework Tools for Visual Studio to help us generate some initial code to map to the database. These tools are just generating code that you could also type by hand if you prefer.

  • Project -> Add New Item…

  • Select Data from the left menu and then ADO.NET Entity Data Model

  • Enter BloggingContext as the name and click OK

  • This launches the Entity Data Model Wizard

  • Select Code First from Database and click Next

  • Select the connection to the database you created in the first section and click Next

  • Click the checkbox next to Tables to import all tables and click Finish

Once the reverse engineer process completes a number of items will have been added to the project, let's take a look at what's been added.

Configuration file

An App.config file has been added to the project, this file contains the connection string to the existing database.

You’ll notice some other settings in the configuration file too, these are default EF settings that tell Code First where to create databases. Since we are mapping to an existing database these setting will be ignored in our application.

Database Generated Key Entity Framework

Derived Context

Database Generated Key Entity Framework Free

A BloggingContext class has been added to the project. The context represents a session with the database, allowing us to query and save data.The context exposes a DbSet<TEntity> for each type in our model. You’ll also notice that the default constructor calls a base constructor using the name= syntax. This tells Code First that the connection string to use for this context should be loaded from the configuration file.

You should always use the name= syntax when you are using a connection string in the config file. This ensures that if the connection string is not present then Entity Framework will throw rather than creating a new database by convention.

Entity

Model classes

Finally, a Blog and Post class have also been added to the project. These are the domain classes that make up our model. You'll see Data Annotations applied to the classes to specify configuration where the Code First conventions would not align with the structure of the existing database. For example, you'll see the StringLength annotation on Blog.Name and Blog.Url since they have a maximum length of 200 in the database (the Code First default is to use the maximun length supported by the database provider - nvarchar(max) in SQL Server).

4. Reading & Writing Data

Now that we have a model it’s time to use it to access some data. 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.

What if My Database Changes?

Database Generated Key Entity Framework For Windows 10

The Code First to Database wizard is designed to generate a starting point set of classes that you can then tweak and modify. If your database schema changes you can either manually edit the classes or perform another reverse engineer to overwrite the classes.

Using Code First Migrations to an Existing Database

If you want to use Code First Migrations with an existing database, see Code First Migrations to an existing database.

Summary

In this walkthrough we looked at Code First development using an existing database. We used the Entity Framework Tools for Visual Studio to reverse engineer a set of classes that mapped to the database and could be used to store and retrieve data.