Using Enum with EF Core

Enumeration types

An enumeration type (or enum type) is a value type defined by a set of named constants of the underlying integral numeric type.

Basic non EF Core example

We want to know if a date is a weekend, we can use DayOfWeek enum.

Helper extension

internal static class DateOnlyExtensions
{
    public static bool IsWeekend(this DateOnly sender)
        => (sender.DayOfWeek == DayOfWeek.Sunday || 
            sender.DayOfWeek == DayOfWeek.Saturday);
}

Mock-up some dates and check for is a DateOnly a weekend.

var dates = Enumerable
    .Range(1, 17)
    .Select(x => new DateOnly(2023, 1, x)).ToList();

foreach (var date in dates)
{
    Console.WriteLine($"{date,-12:MM/dd/yyyy}" + 
                      $"{date.IsWeekend(),-10}{date.DayOfWeek}");
}

Results

01/01/2023  True      Sunday
01/02/2023  False     Monday
01/03/2023  False     Tuesday
01/04/2023  False     Wednesday
01/05/2023  False     Thursday
01/06/2023  False     Friday
01/07/2023  True      Saturday
01/08/2023  True      Sunday
01/09/2023  False     Monday
01/10/2023  False     Tuesday
01/11/2023  False     Wednesday
01/12/2023  False     Thursday
01/13/2023  False     Friday
01/14/2023  True      Saturday
01/15/2023  True      Sunday
01/16/2023  False     Monday
01/17/2023  False     Tuesday

EF Core example

In this example we want to associate wines with wine types in a SQL-Server database table.

Figure 1

Note
The table WineType is not used in code, it is for a T4 template discussed later, for now we are only interested in the Wine table.

Wine model where WineType is an enum.

public class Wine
{
    public int WineId { get; set; }
    public string Name { get; set; }
    public WineType WineType { get; set; }
    public override string ToString() => $"{WineType} {Name}";
}

WineType enum

public enum WineType
{
    [Description("Classic red")]
    Red = 1,
    [Description("Dinner white")]
    White = 2,
    [Description("Imported rose")]
    Rose = 3
}

To configure, in the DbContext, OnModelCreating setup an association between WineType to int as follows.

This allows us to, in this case query for a specific wine type as follows.

namespace EnumHasConversion.Classes;

public class WineOperations
{
    public static List<Wine> GetWinesByType(WineType wineType)
    {
        using var context = new WineContext();
        return context.Wines
            .Where(wine => wine.WineType == wineType)
            .ToList();
    }

}

Call above method.

List<Wine> redWines = WineOperations.GetWinesByType(WineType.Red);

T4 Template

The reason for using a template is for sharing the enum between applications and ensuring members are up to date. This is done by creating a T4 template that reads from a SQL-Server database table which is shown figure 1.

Usually a T4 is updated on change which means if data is modified in the database someone needs to inform the developer and in turn the developer must make a small change to the template or delete the associated .cs file, or automate the process via MS-Build: Invoke text transformation in the build process.

Note
There is a model in the source code which is for ensuring there is a table for the template to work with for demo purposes only.

[Table("WineType")]
public class WineTypes
{
    [Key]
    public int Id { get; set; }
    public string TypeName { get; set; }
    public string  Description { get; set; }
}

In our DbContext OnModelCreating

modelBuilder.Entity<WineTypes>().HasData(
    new WineTypes() {Id = 1, TypeName = "Red", Description = "Classic red"},
    new WineTypes() {Id = 2, TypeName = "White", Description = "Dinner white"},
    new WineTypes() {Id = 3, TypeName = "Rose", Description = "Imported rose"}
);

Summary

Using enums in C# with EF Core is extremely easy and note that the use of a T4 template is completely optional, without a T4 template simply create a regular enum.

Source code

Clone the following GitHub repository, run the project.

The first time running the project the database is created and populated then afterwards data is read.

Requires

• Microsoft Visual Studio 2022 or higher version 17.4.x