在控制台应用程序的OnConfiguring方法中使用依赖注入获取连接字符串？

Question

In a .NET Core Console Application I have the following DbContext:

public class AppDataContext : DbContext 
{

    public DbSet<ExampleObject> ExampleObjects { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseNpgsql(/* Read Connection String from appsettings.json */);
    }

}

Of course I could instantiate the ConfigurationBuilder class and access the connectionString, like this:

var builder = new ConfigurationBuilder()
  .SetBasePath(Directory.GetCurrentDirectory())
  .AddJsonFile("appsettings.json");
Configuration = builder.Build();

var connString = Configuration.GetConnectionString("data"));

but how can I force Entity Framework to use the IConfigurationRoot instance defined with dependency injection?

Thank you

Answer 1

You're approaching it from the wrong angle. You're currently trying to "bring in" configuration. What you need to be doing is "applying" the configuration at the ServiceCollection level so that the Net Core Dependency Injection can instantiate your DbContext with the correct values automatically. Here is an example of how to do that:

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<BloggingContext>(options => options.UseSqlite("Data Source=blog.db"));
}

Of course you can still use the IConfigurationBuilder to get your connection string - that would go in the ConfigureServices section above and "Data Source=blog.db" would be swapped for your value

Your DbContext can then be simplified like this:

public class AppDataContext : DbContext 
{
    public DbSet<ExampleObject> ExampleObjects { get; set; }
}