I want to be able to create a database context with entityframework core in my webapi project using the database first approach.
When I create like this it works very well

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

            public TestingContext()
            {
            }

            protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            {
                optionsBuilder.UseSqlServer("Data Source=xxxxxx;Initial Catalog=xxxxxx;Integrated Security=False;User Id=xxxxx;Password=xxxxx;MultipleActiveResultSets=True");

            }

            public DbSet<Information> Information { get; set; }
            public DbSet<ArticleUser> ArticleUser { get; set; }

        }

```

I had to add the line services.AddDbContext to make it work.

```
     public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();
            services.AddCors();
            //using Dependency Injection
            services.AddSingleton<Ixxx, xxx>();

            // Add framework services.

            services.AddApplicationInsightsTelemetry(Configuration);
            services.AddDbContext<TestingContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

            // Register the Swagger generator, defining one or more Swagger documents
            services.AddSwaggerGen(c =>
            {
                c.SwaggerDoc("v1", new Info { Title = "Articles API", Version = "v1" });
            });

        }

```

If I remove this method from my TestingContext 

```
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer("Data Source=xxxxxx;Initial Catalog=xxxxxx;Integrated Security=False;User Id=xxxxx;Password=xxxxx;MultipleActiveResultSets=True");

    }

```

I get the error below.

No database provider has been configured for this DbContext. 
A provider can be configured by overriding the DbContext.OnConfiguring method or 
by using AddDbContext on the application service provider. If AddDbContext is used, 
then also ensure that your DbContext type accepts a DbContextOptions object in its 
constructor and passes it to the base constructor for DbContext.

Why do I need to pass my connection string to the database in two places before it can pull my data. Please assist. I am new to the core. The two places are configure services method and the context itself.