Using Mockaroo and Entity framework to Seed Sample Data for .NET Applications

#dotnet #csharp #sqlserver #webdev

Testing your applications thoroughly requires diverse sample data that's often time-consuming to create manually. Mockaroo simplifies this process by generating realistic test data quickly, and today we'll explore how to use it.

The only thing you’ll need for this tutorial is Visual Studio community edition. You can download it here

Create a Dataset in Mockaroo

Navigate to the Mockaroo Website,
and define the Dataset fields, I have defined mine like so;

Since we’re going to seed the data through EF Core, we’ll select the output format as JSON.

Click on GENERATE DATA and the output file should be downloaded.

Create a Web API project

Open up Visual Studio and click Create a new Project
In the Search Template field, search for ASP.NET Core Web API and click on it.

Give your project a name, I have called mine Mockaroo_Test, then Select .NET 10 as the target framework and leave all the other options as the default values then click Create.

Next, we’re going to install the necessary packages into our project, so open up the package manager console and type in the following commands;

Install-Package Microsoft.EntityFrameworkCore

Install-Package Microsoft.EntityFrameworkCore.InMemory

Install-Package Microsoft.EntityFrameworkCore.Design

Next, Create the a class that has the same structure as the Mockaroo DataSet options we defined earlier

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

        [JsonPropertyName("club_name")]
        public string ClubName { get; set; }

        [JsonPropertyName("country_location")]
        public string CountryLocation { get; set; }

        [JsonPropertyName("stadium_capacity")]
        public int StadiumCapacity { get; set; }

        [JsonPropertyName("manager_name")]
        public string ManagerName { get; set; }

        [JsonPropertyName("founded_year")]
        public int FoundedYear { get; set; }

        [JsonPropertyName("league_affiliation")]
        public string LeagueAffiliation { get; set; }

        [JsonPropertyName("captain_name")]
        public string CaptainName { get; set; }

        [JsonPropertyName("jersey_color")]
        public string JerseyColor { get; set; }

        [JsonPropertyName("average_attendance")]
        public int AverageAttendance { get; set; }

        [JsonPropertyName("major_rival")]
        public string MajorRival { get; set; }
    }

Now, create a new class called AppDbContext and copy this code into it;

   public class AppDbContext : DbContext
   {
       public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
       {
       }
       public DbSet<Club> Clubs { get; set; }
   }

Since we’re using an Inmemory database, we need to wire it up in our application, so navigate to the Program.cs class and add this piece of code;

builder.Services.AddDbContext<Mockaroo_Test.AppDbContext>(options =>
{
    options.UseInMemoryDatabase("MockarooDemoDb");
});

Seeding the Data

The next step is to move the .json file downloaded from Mockaroo into your application folder, like so;

Let's then create the class the serializes the data. Do that by creating a class called SeedData and adding this code to it;

    public class SeedData
    {
        public static async Task SeedAsync(AppDbContext context)
        {
            if (context.Clubs.Any()) return;

            var json = await File.ReadAllTextAsync("MOCK_DATA.json");
            var clubs = JsonSerializer.Deserialize<List<Club>>(json);

            context.Clubs.AddRange(clubs!);
            await context.SaveChangesAsync();
        }
    }

The SeedAsync method loads starter information about clubs into the system. It first checks if any clubs already exist, and if the system is empty, it reads club details from a file, converts that information into a usable format, and stores it in the database.

Navigate back to Program.cs and add this piece of code to wire everything up;

using (var scope = app.Services.CreateScope())
{
    var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
    await SeedData.SeedAsync(db);
}

NB; This code snippet should come after the declaration of the app variable

var app = builder.Build();

And that’s it, If you run the application the MockarooDemoDb Database gets seeded with data from our MOCK_DATA.json file.

We can go one step further and visualize the data to make sure.

In the Controllers folder, Create a class called ClubController with this piece of code;

[ApiController]
[Route("api/[controller]")]
public class ClubContronller : ControllerBase
{
    private readonly AppDbContext _context;

    public ClubContronller(AppDbContext context)
    {
        _context = context;
    }

    [HttpGet]
    public async Task<ActionResult<List<Club>>> Get()
    {
        var clubs = await _context.Clubs.ToListAsync();
        return Ok(clubs);
    }
}