Build ASP.NET Core API Using Existing Database

Step 7. If everything looks good, it's time to introduce the EF core in the project. We are using the EF core database first approach in this post. You have an existing database, using the Scaffold-DbContext command, you can generate entity and context classes based on the schema of the existing database. For the same go step by step.

1. Open Package Manager Console(From the View menu, select Other Windows > Package Manager console. )
2. Install below the NuGet package one by one.

Install-Package Microsoft.EntityFrameworkCore.SqlServer -Version 3.0.0

Install-Package Microsoft.EntityFrameworkCore.Design -Version 3.0.0

Install-Package Microsoft.EntityFrameworkCore.Design -Version 3.0.0

Step 8. Now it's time to generate entity and context classes, run the following command in the Package Manager console (Replace your connection string as well).

Scaffold-DbContext "Server=.;Database=CoreApi;Trusted_Connection=True;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir Models -Context CoreDbContext -DataAnnotations

Step 9. Now it's time to add the Connection string to your app settings file. Add the below lines to appsettings.json.

"ConnectionStrings": {
    "Database": "YourConnectionString"
}

Your app settings JSON file should be or maybe similar to the below Snippet.

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "ConnectionStrings": {
    "Database": "Server=(local);Database=CoreApi;Trusted_Connection=True;"
  },
  "AllowedHosts": "*"
}

Step 10. Now it's time to add the DbContext to your Startup file. Add the below lines to Startup. cs.

services.AddDbContext<CoreDbContext>(op => op.UseSqlServer(Configuration.GetConnectionString("Database")));    

Your Startup Class should be similar to the below Snippet:

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<CoreDbContext>(op => op.UseSqlServer(Configuration.GetConnectionString("Database"))); //Add
        services.AddControllers();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        app.UseHttpsRedirection();
        app.UseRouting();
        app.UseAuthorization();
        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
    }
}

Step 11. Now, your web API is ready to build and run.

Closing

In this article, I built a new core web API project as a test project. This example is very basic and a perfect initial point to creating an awesome API. You can visit this git repository for a better understanding of this project. I will let you know about the implementation of Swagger documentation in the same API Project in my next post. If you like this article, feel free to share it with your friends.