Entity Framework Core 5 is a light and easy to use ORM, that let you use the database without writing any SQL commands. Built-in mechanisms will translate your LINQ queries on your entity classes to SQL queries and return mapped objects.

Here is an article about adding EF Core with migrations to an empty database: PrimeHotel – adding Entity Framework Core 5 in .NET

Adding an Entity Framework Core 5 is super simple if you have an empty database, but is it that easy when working with a database that has some data inside? Do we need to map it all, or can we just work with a part of the database that interests us? Let’s start from the beginning.

Let’s see what we need

To work with EF Core 5 we need to install NuGet packages:

• Microsoft.EntityFrameworkCore
• Microsoft.EntityFrameworkCore.Design
• Microsoft.EntityFrameworkCore.SqlServer

The last one reveals that we will work with the MS SQL Server database. Now let’s connect to our database and see how it looks like.

I’m using an Azure Data Studio, which is a lightweight and fast tool that can perform most of the basic operations of databases. It’s much faster than SQL Server Management Studio and now for most of my work, I just use the first one.

We will add EF Core for aspnetcore database, which looks like this.

We need a DbContext

The next thing we need to do is to create our DbContext. We could create it by hand and type everything manually. However, .NET Core has tools to scaffold that and generate it for us.

The process is called reverse engineering and it is scaffolding entity type classes and a DbContext class based on a database schema. To perform this operation we will use the .NET CLI tool, that you would have to install if you haven’t done it already. Type this command to check it out:

dotnet tool install --global dotnet-ef

You can also update the tool, once installed:

The scaffolding process needs a connection string to pass. We could pass it in our command, but we can also accomplish this task in a more elegant way by passing only its name.

Let’s go to the appsettings.json file and set up a connection string for our new database.

I’ve added a connection string with the name aspnetcore in ConnectionStrings section. 

The command that we are going to use is very simple, run it in your project directory:

dotnet ef dbcontext scaffold Name=aspnetcore Microsoft.EntityFrameworkCore.SqlServer

This command will add aspnetcoreDbContext and all entities representing your database.

However, it would be nice to have some more control over the process.

Customize the process to your needs

Thankfully, there are more parameters that we can use. Let’s take a look at some of them:

• --table can be used to include specific tables
• --use-database-names option will preserve the original database names as much as possible. However, invalid .NET identifiers will still be fixed
• --context can be used to give generated DbContext your own name
• --context-dir can be used to scaffold the DbContext class to a specific directory
• --output-dir can be used to scaffold entity classes to a specific directory
• --force will override the existing DbContext class and entity classes

I’m going to modify my command, so it will look like this:

dotnet ef dbcontext scaffold Name=aspnetcore --table Profiles --table Events
  --context AspNetCoreDbContext --context-dir AspNetCoreModels 
  --output-dir AspNetCoreModels Microsoft.EntityFrameworkCore.SqlServer

Let’s see what classes were generated.

Notice that only tables Events and Profiles were generated, DbContext class is named AspNetCoreCotext and all was generated in AspNetCoreModels directory. Awesome! 

The limitations

Reverse engineering does a tremendous job of scaffolding entity classes so that we don’t need to write it on our own. However, there are some limitations to this process:

• not everything about the model is presented in the database schema. For example inheritance hierarchies, owned types and table splitting will not be reverse-engineered
• also, EF Core documentation claims, that there are some column types that will not be included in the model
• nullable types will not be mapped as nullable. For example, string columns that can be null, will not be scaffolded as string? type. You will have to edit it yourself

More of that you can read in this Microsoft article.

Updating the model

Whenever something changes in the database, you would need to update your model. Most of the changes will be trivial, like adding a column to the table, renaming a table name, or change columns type. Those changes can be quickly applied in the entity classes manually. 

However, if you’re not sure how to map your changes, you can always regenerate the whole DbContext with all entity classes. To do this, use --force parameter in the scaffold command. Note, however, that all changes done manually, will be overwritten. Currently, there is no option to update model from database schema and preserve manual changes.

Updating the database

Scaffolding a DbContext is just a way to generate classes, that match the database. This means that you can add migrations even to an existing database.

First, you would need to add AspNetCoreDbContext to your DI container. Go to the Startup.cs file and in ConfigureServices add the following line.

    services.AddDbContext<AspNetCoreDbContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("aspnetcore")));

Now you can add migrations to the second database. It’s a good practice to keep models and migrations separate for every database. Execute this command:

dotnet ef migrations add InitialCreate --context AspNetCoreDbContext --output-dir Migrations/AspNetCore

Here is what was generated:

There’s one thing worth noticing. Entity Framework Core generated initial migration with all changes that are currently in the AspNetCoreDbContext. You might need to clear all changes in that migration because those tables already exist.

Summary

When adding an Entity Framework Core 5 to an existing database, a good idea is to scaffold entity classes and context with a dedicated .NET CLI tool. You have a handful of parameters that you can provide and scaffold exactly what you need and how you need it.

You can add EF Core 5 migrations later on for keeping your database up to date with your code. One thing that you should keep in mind is that updating DbContext from the database again will override all changes that you did manually. Because of this, scaffolding DbContext is more of a one-time thing.

All code posted here was applied to a PrimeHotel project, that is available at my GitHub, so you can download it freely and experiment. Take a look also at this post on how to run it: PrimeHotel – how to run this project.

Hope you liked the post, cheers!

Let’s have a look at how to introduce Entity Framework Core 5 in ASP.NET Core project in .NET 5. We will start from an empty database, where we have a clean slate and can add tables the way we want.

In this post we will work with the PrimeHotel project, that was created for learning purposes. It’s all available at my GitHub, so you can download it freely. Take a look also at this post on how to run it: PrimeHotel – how to run this project.

What is Entity Framework Core

Entity Framework Core 5 is a lightweight, extensible, open-source, and cross-platform version of the popular Entity Framework data access technology. EF Core is an object-relational mapper (O/RM), enables developers to work with a database using .NET objects, and eliminating the need for most of the data-access code they usually need to write. This means no more SQLs. It proves to be great for most of the scenarios, however, when you need to work with big amounts of data, you might be better off with writing SQLs.

Adding an Entity Framework Core

Adding EF Core to an ASP.NET Core project is super easy. Start with installing NuGet packages:

• Microsoft.EntityFrameworkCore
• Microsoft.EntityFrameworkCore.Design
• Microsoft.EntityFrameworkCore.SqlServer

Once it’s all done, add a PrimeDbContext in the Models folder, that would look like this:

    public class PrimeDbContext : DbContext
    {
        public PrimeDbContext(DbContextOptions<PrimeDbContext> options)
            : base(options)
        {
        }

        public virtual DbSet<Room> Rooms { get; set; }
    }

Now we need to add a Room class, that would represent an entity of a room, from Rooms table.

    public class Room
    {
        public int Id { get; set; }

        public int Number { get; set; }

        public string Description { get; set; }

        public DateTime LastBooked { get; set; }

        public int Level { get; set; }

        public RoomType RoomType { get; set; }

        public int NumberOfPlacesToSleep { get; set; }
    }

    public enum RoomType
    {
        Standard,
        Suite
    }

Now let’s handle the configuration part. Let’s use an empty database, that is hosted by us locally. The easiest approach is to install SQL Server Express edition and setup it locally. However, you can set up your database server in the docker container. Check my post on how to do it: Set up a SQL Server in a docker container.

In appsettings.json file we need to set our connection string. It should look similar to this:

Now let’s go to the Startup.cs file, where we need to configure EF Core to use our connection string. In ConfigureServices method, add this line:

    // Entity Framework
    services.AddDbContext<PrimeDbContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("HotelDB")));

Notice that I used a HotelDB name, that is a name of my connection string in the appsettings.json file.

We have most of the crucial things done, but we need something, that would create tables in DB from our PrimeDbContext. So far we got only one, but it’s the right time to introduce migration mechanisms.

Adding EF Core migrations

Migrations in the EF Core database allow you to make changes to the database so that it is in line with the code of the application that uses it. This is a very important mechanism because changes in the structure of the database are introduced quite often, even by many programmers, so we need a universal mechanism to track and introduce these changes.

Adding first migration doesn’t differ much from adding the next ones. You need to open a terminal window in the location of the project and execute the command:

dotnet ef migrations add InitialCreate

When this command executes successfully, it will generate a migration file, where you can check what changes will be applied.

In this file you will find two methods: Up and Down. Those will represent the changes when migration will be applied and when it would be rolled back.

    public partial class InitialCreate : Migration
    {
        protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.CreateTable(
                name: "Rooms",
                columns: table => new
                {
                    Id = table.Column<int>(nullable: false)
                        .Annotation("SqlServer:Identity", "1, 1"),
                    Number = table.Column<int>(nullable: false),
                    Description = table.Column<string>(nullable: true),
                    LastBooked = table.Column<DateTime>(nullable: false),
                    Level = table.Column<int>(nullable: false),
                    RoomType = table.Column<int>(nullable: false),
                    NumberOfPlacesToSleep = table.Column<int>(nullable: false)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_Rooms", x => x.Id);
                });
        }

        protected override void Down(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.DropTable(
                name: "Rooms");
        }
    }

The last thing left to do is to trigger updating the database. It would be great if our changes were checked and applied on every project run. Let’s see how we can accomplish that. First of all, let’s go to Startup.cs file and create a method. 

    private void UpgradeDatabase(IApplicationBuilder app)
    {
        using (var serviceScope = app.ApplicationServices.CreateScope())
        {
            var context = serviceScope.ServiceProvider.GetService<PrimeDbContext>();
            if (context != null && context.Database != null)
            {
                context.Database.Migrate();
            }
        }
    }

This method will use built-in Dependency Injection mechanism to fetch an instance of our PrimeDbContext and use it to run database migrations. Only ones that were not applied yet will be run.

Now, in the Configure method add a line at the bottom.

    UpgradeDatabase(app);

If we take a look into the database, we will see what migrations were applied. __EFMigrationsHistory table is created automatically by Entity Framework Core.

Using EF Core 5

Once we have everything in place, we have a proper configuration and database migrations, we can start benefit from having an O/RM mechanism.

All operations on tables in EF Core needs to go through PrimeDbContext. Using it is super simple, once we registered it in Startup.cs class, it will be available in any class for us to use. Take a look at this example of simple CRUD operations in the RoomController.

    [ApiController]
    [Route("[controller]")]
    public class RoomController : ControllerBase
    {
        private readonly PrimeDbContext primeDbContext;

        public RoomController(PrimeDbContext _primeDbContext)
        {
            primeDbContext = _primeDbContext;
        }

        [HttpGet]
        public async Task<IEnumerable<Room>> Get()
        {
            return await primeDbContext.Rooms.ToListAsync();
        }

        [HttpGet("{id}")]
        public async Task<IActionResult> Get(int id)
        {
            var room = await primeDbContext.Rooms.FindAsync(id);
            if (room == null)
            {
                return NotFound();
            }

            return Ok(room);
        }

        [HttpPost]
        public async Task<IActionResult> Post([FromBody] Room room)
        {
            var createdRoom = await primeDbContext.Rooms.AddAsync(room);
            await primeDbContext.SaveChangesAsync();

            return Ok(createdRoom.Entity);
        }

        [HttpPut]
        public async Task<IActionResult> Put([FromBody] Room room)
        {
            var existingRoom = await primeDbContext.Rooms.FindAsync(room.Id);
            if (existingRoom == null)
            {
                return NotFound();
            }

            existingRoom.Number = room.Number;
            existingRoom.Description = room.Description;
            existingRoom.LastBooked = room.LastBooked;
            existingRoom.Level = room.Level;
            existingRoom.RoomType = room.RoomType;
            existingRoom.NumberOfPlacesToSleep = room.NumberOfPlacesToSleep;

            var updatedRoom = primeDbContext.Update(existingRoom);
            await primeDbContext.SaveChangesAsync();
            return Ok(updatedRoom.Entity);
        }

        [HttpDelete("{id}")]
        public async Task<IActionResult> Delete(int id)
        {
            var existingRoom = await primeDbContext.Rooms.FindAsync(id);
            if (existingRoom == null)
            {
                return NotFound();
            }

            var removedRoom = primeDbContext.Rooms.Remove(existingRoom);
            await primeDbContext.SaveChangesAsync();

            return Ok(removedRoom.Entity);
        }
    }

Notice that in EF Core there is an asynchronous version of every method. Taking advantage of this is a good idea. This way your code will be faster and could be run more efficiently with many other requests in parallel.

Important things to have in mind:

• we can query entities collections the way we want with LINQ using Where, Select and other methods and that will generate SQL out of all those conditions
• If you’re just querying entities, you can use AsNoTracking() to improve performance
• A call to the database will be performed when the code we write needs the results. This is for example where we use ToListAsync
• All changes that we make needs to be saved with SaveChangesAsync to be applied

Those are only a few points to have in mind, but there us much more that is going underneath to be aware of. However, this is good for a start, and it more than enough to play with Entity Framework Core on your own.

Summary

Nice and clean! Entity Framework Core is perfect for almost every simple database usage. I’m sure you’ll find it useful and intuitive.

All code posted here is available at my GitHub, so you can download it freely. Take a look also at this post on how to run it: PrimeHotel – how to run this project.

Thanks for reading, let me know if you liked this post 🙂