Enum Support - Code First

Straipsnis
10/14/2020

Note

EF5 Onwards Only - The features, APIs, etc. discussed in this page were introduced in Entity Framework 5. If you are using an earlier version, some or all of the information does not apply.

This video and step-by-step walkthrough shows how to use enum types with Entity Framework Code First. It also demonstrates how to use enums in a LINQ query.

This walkthrough will use Code First to create a new database, but you can also use Code First to map to an existing database.

Enum support was introduced in Entity Framework 5. To use the new features like enums, spatial data types, and table-valued functions, you must target .NET Framework 4.5. Visual Studio 2012 targets .NET 4.5 by default.

In Entity Framework, an enumeration can have the following underlying types: Byte, Int16, Int32, Int64 , or SByte.

Watch the video

This video shows how to use enum types with Entity Framework Code First. It also demonstrates how to use enums in a LINQ query.

Presented By: Julia Kornich

Video: WMV | MP4 | WMV (ZIP)

Pre-Requisites

You will need to have Visual Studio 2012, Ultimate, Premium, Professional, or Web Express edition installed to complete this walkthrough.

Set up the Project

Open Visual Studio 2012
On the File menu, point to New, and then click Project
In the left pane, click Visual C#, and then select the Console template
Enter EnumCodeFirst as the name of the project and click OK

Define a New Model using Code First

When using Code First development you usually begin by writing .NET Framework classes that define your conceptual (domain) model. The code below defines the Department class.

The code also defines the DepartmentNames enumeration. By default, the enumeration is of int type. The Name property on the Department class is of the DepartmentNames type.

Open the Program.cs file and paste the following class definitions.

public enum DepartmentNames
{
    English,
    Math,
    Economics
}     

public partial class Department
{
    public int DepartmentID { get; set; }
    public DepartmentNames Name { get; set; }
    public decimal Budget { get; set; }
}

Define the DbContext Derived Type

In addition to defining entities, you need to define a class that derives from DbContext and exposes DbSet<TEntity> properties. The DbSet<TEntity> properties let the context know which types you want to include in the model.

An instance of the DbContext derived type manages the entity objects during run time, which includes populating objects with data from a database, change tracking, and persisting data to the database.

The DbContext and DbSet types are defined in the EntityFramework assembly. We will add a reference to this DLL by using the EntityFramework NuGet package.

In Solution Explorer, right-click on the project name.
Select Manage NuGet Packages…
In the Manage NuGet Packages dialog, Select the Online tab and choose the EntityFramework package.
Click Install

Note, that in addition to the EntityFramework assembly, references to System.ComponentModel.DataAnnotations and System.Data.Entity assemblies are added as well.

At the top of the Program.cs file, add the following using statement:

using System.Data.Entity;

In the Program.cs add the context definition.

public partial class EnumTestContext : DbContext
{
    public DbSet<Department> Departments { get; set; }
}

Persist and Retrieve Data

Open the Program.cs file where the Main method is defined. Add the following code into the Main function. The code adds a new Department object to the context. It then saves the data. The code also executes a LINQ query that returns a Department where the name is DepartmentNames.English.

using (var context = new EnumTestContext())
{
    context.Departments.Add(new Department { Name = DepartmentNames.English });

    context.SaveChanges();

    var department = (from d in context.Departments
                        where d.Name == DepartmentNames.English
                        select d).FirstOrDefault();

    Console.WriteLine(
        "DepartmentID: {0} Name: {1}",
        department.DepartmentID,  
        department.Name);
}

Compile and run the application. The program produces the following output:

DepartmentID: 1 Name: English

View the Generated Database

When you run the application the first time, the Entity Framework creates a database for you. Because we have Visual Studio 2012 installed, the database will be created on the LocalDB instance. By default, the Entity Framework names the database after the fully qualified name of the derived context (for this example that is EnumCodeFirst.EnumTestContext). The subsequent times the existing database will be used.

Note, that if you make any changes to your model after the database has been created, you should use Code First Migrations to update the database schema. See Code First to a New Database for an example of using Migrations.

To view the database and data, do the following:

In the Visual Studio 2012 main menu, select View -> SQL Server Object Explorer.
If LocalDB is not in the list of servers, click the right mouse button on SQL Server and select Add SQL Server Use the default Windows Authentication to connect to the LocalDB instance
Expand the LocalDB node
Unfold the Databases folder to see the new database and browse to the Department table Note, that Code First does not create a table that maps to the enumeration type
To view data, right-click on the table and select View Data

Summary

In this walkthrough we looked at how to use enum types with Entity Framework Code First.

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