APIs with Entity Framework Core

In this new post, I want to give a complete example of minimal APIs in Blazor with Entity Framework Core with complex objects. I always struggle to have a solution working when my model has dependencies with other object. Here I show my test and my code. The code is in NET9. In the Microsoft documentation, there are some examples but it is not complex enough. A few days ago, I posted about another problem I had with NET9 and Entity Framework Core.

The full source code of this post is available on GitHub. If you have any questions, please comment below or post in the forum.

The complete code is spanned through those posts:

• APIs with Entity Framework Core
• APIs with Entity Framework Core: POST
• APIs with Entity Framework Core: PUT

Scenario

Very often in my projects, I want to save the data in the database. I always use the models I created in the Domain project. This is because I like to have a clear code as I explained in my earlier post. Let me clear my common problem.

Joined tables

So, let me show a real database I’m working on. As you can see I have a few tables but not all of them are coming strictly from the code. The tables Clients, ClientAddresses and tbl_Channels are created from the Domain. ChannelClient is a joined table that Entity Framework Core is creating automatically.

To avoid distractions, I only show the code necessary to create the tables with minimal data. So, I can focus only on the implementation of the code to insert or update in the database the data. Once the logic is clear, it is easy to extend it to other fields.

Tables explanation

Now, the implementation has 4 tables. As I said, 3 are generated from the code. One is generated from Entity Framework Core as a joined table. Why? Here is an example. In your form, you have a dropdown list with multiple choices. By the way, in this example, I use my AutoComplete component for Blazor.

The list is from the tbl_Channels table. Because the user can choose more than one option, the database has to save all of them. That means, for a client I have to save one or more records. This is a N:M relation. There are several Clients per Channel and the same Client has several Channels. For example: Channel 1 has Channels 1,2,5, Client 1 has Channels 1,2

Domain implementation

As I mentioned before, the model to create the database lies in the Domain layer. So, I created a new project for it.

Channel

This table contains the items to display in the dropdown list. The user can select one or more of them. The implementation is quite simple.

[Table("tbl_Channels")]
public class Channel
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    [JsonPropertyName("Id")]
    public long Id { get; set; }

    [Required]
    [JsonPropertyName("name")]
    public string? Name { get; set; }

    [JsonIgnore]
    public ICollection<Client>? Client { get; set; }
}

Table attribute defines the name of the table in the database. Key attributes defined this field as a key and it is generated automatically by the database. JsonPropertyName defines the name of the fields when the application reads or returns this object via API. JsonIgnore attribute means that this field won’t be added in the json. I added this attribute to avoid recursion when the json will be created.

Now, I want to link this table with the Client table. For that, I added an ICollection of Client that is the model I’m going to create now.

Clients

This table contains the list of clients. Also, here I have to define the link with the Channel table.

Now, I continue with the explanation of how to use APIs with Entity Framework Core and later I will add the ClientAddress table.

Persistence and migrations

Now, because I want to create this project as a future reference, I am going to create a Persistence layer. Generally speaking, this is where I will create the implementation for the repositories and the context. Also, in this project, I will add the migration using Entity Framework Core.

To give you more info, I recorded a video how I create the Persistence project. Also, you see how I generate the migration using Entity Framework Code. In this project, I will add the context for the database and the service registration for this layer (and the context). The project is called APIEFCore.Persistence.

Create MyDbContext

First, I have to add the creation of the database context. For that, I created a file called MyDbContext and the content is the following

public class MyDbContext : DbContext
{
    public MyDbContext(DbContextOptions<MyDbContext> option) : base(option)
    {
    }

    public DbSet<Client> Clients { get; set; }
    public DbSet<Channel> Channels { get; set; }
}

Whit this code, I tell the Entity Framework Core that the context contains 2 tables. Those tables can be used with the names Clients and Channels.

Registration service

Now, because I want to use this project as a reference, I also created a persistence service registration to register the context and other services in the IServiceCollection. The code is the following

public static class PersistenceServiceRegistration
{
    public const string ConnectionName = "DefaultConnection";

    public static IServiceCollection AddPersistenceServices(this IServiceCollection services,
        IConfiguration configuration,
        string cnnStringName = ConnectionName,
        string? cnnString = null)
    {
        if (cnnString == null)
            cnnString = configuration.GetConnectionString(cnnStringName);

        services.AddDbContext<MyDbContext>(options => options.UseSqlServer(cnnString));

        return services;
    }
}

In order to register this code, I have to add in the server project in the builder this service using this line:

builder.Services.AddPersistenceServices(builder.Configuration);

After that, I can use the database and the context in the application.

Create migration

Now, I have to generate the code to create the database. For that, I use what Entity Framework offers. I open the Package Manager Console and here I start to add the migration for the context. Because the solution I created is based on Blazor with Individual Authentication, in the project there are 2 contexts. I created MyDbContext but for the project I have the ApplicationDbContext. So, I have to specified what context I want to use. In the app.settings.json I can see the connection string for the database that is for a MSSQLLocalDb.

So, to generate the initial migration for my context, in the Package Manager Console, I have to run the following command

add-migration InitialMigration -Context MyDbContext

With that, Entity Framework generates the migration for this context.

Update database

Now that the migration is created, I can update the structure of the database. As I said, I have 2 contexts and for that I have to run twice the update.

Starting with the ApplicationDbContext, in the Package Manager Console, I am going to run the following command

update-database -Context ApplicationDbContext

This is creating the tables for the ASPNET Users and Roles tables that I discussed a lot in my earlier posts. Remember to specify the context. Now, I can run a similar command for my context

update-database -Context MyDbContext

The result of all of it is the creation of the tables as shown in the following screenshot.

In the video, I show the structure of the tables that is what you see at the top of this post.

Minimal APIs creation

The next step is to create the minimal APIs based on the models I created in the Domain layer. Also, for this step I created a video. To generate the APIs, I am going to use Visual Studio and in particular the Scaffolded Item.

Now, with this tool, I can generate an API based on my model and Entity Framework. So, select the option API with read/write endpoints, using Entity Framework.

Then, I have to choose the following fields:

• Model class: one of the models in the Domain layer
• Endpoints class: I like to create a new file for each model
• DbContext: that in this case is MyDbContext

After that, I want to use OpenAPI and TypedResults as checked by default.

After the first endpoint for Client is created, I want to add another one for Channel. I can’t execute the procedure again because it returns an error. For that, go to the Program.cs in the server project and commend

app.MapClientEndpoints();

After that, I can generate a new API using the New Scaffolded Item option. I’m not sure if it is possible to avoid this error in some way. If you comment this line, it is working.

Swagger

Now, Swagger is added automatically to the project. So, I can play with it. If you use my project, the link is

https://localhost:7191/swagger/index.html

If I try to create a new Channel, it is working and I can see that APIs with Entity Framework Core are there. But this is only the beginning.

Wrap up

In conclusion, in this first post of APIs with Entity Framework Core, I show you how to set the basis of the project and how:

• to create the APIs using the Scaffolded tool
• the create the database.

The difficult part is coming! I have to start to change the code to add the channels to the client. Also, I want to update this record. How can I do it? Soon the next post.

Happy coding!