Pass connection string to .Net Core EF library from another library

Question

I have an ASP.NET Core application, which is structured in three layers i.e.:

Data access layer (Entity Framework)
Business logic layer
ASP.NET MVC web application

As it is right now, the configuration works, and I can access my database in my web application library. However, when I constructed my data access layer with EF Db first, I got a generic class, which looks something like this:

public partial class ClassContext: DbContext
{
    public ClassContext(DbContextOptions<ClassContext> options)
        : base(options)
    {
    }

    public virtual DbSet<Entity> Entity{ get; set; }
    ....

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        if (!optionsBuilder.IsConfigured)
        {
            optionsBuilder.UseSqlServer("ConnString");
        }
    }
}

As you can see, the connection string is hardcoded into my OnConfiguring method, which is not recommended.

Therefore, I followed the following "guide" here, which suggest me to use the built in DI, to pass the connection string from my Web library.

This I did:

public void ConfigureServices(IServiceCollection services)
{
    //Add connectionstring to EF
    services.AddDbContext<ClassContext>(options => options.UseSqlServer(Configuration.GetConnectionString("ConnectionStringFromAppSettings")));
}

According to the "guide" the connectionstring should be provided to the constructor of my ClassContext class - and it sort of does, however not with any connection string..

This means, that optionsBuilder.IsConfigured evaluates false, and wants to use the hard coded connectionstring.

Therefore, I would very much like to know, if I use the DI incorrect, since i cannot access the connection string in my ClassContext class

Update

I removed the OnConfiguring() method, and do now inject the context into my service class constructor in the business logic layer the following way:

public MasterService(ClassContext context)
{
    MinorService = new MinorService(context);
}

public Stuff AddStuffIntoDatabase(Stuff test)
{
    //business logic going before here
   MinorService.addstuffMethod(test) 
}

However, now I get the following error, when I want to do an operation in my database:

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.

This did not happen before, when I configured the connectionstring wrongly in my OnConfiguring() method.

You don't have to add the connectionstring again in the OnConfiguring method. That method is called before the DbContext is configured. That is why it evaluates to false. Just adding the connectionstring in ConfigureServices is enough. The DbContextOptionsBuilder will already be configured to use sql server when OnConfiguring is called. — Jesse de Wit
Thank you for your answer, I have just made an update to my question :-) — Jeppe Christensen
Maybe this will help you: stackoverflow.com/a/57980799/3883866 — Jesse de Wit

FandangoOnCore FandangoOnCore · Accepted Answer · 2020-02-20T00:05:40

What about the appsettings.json? Is it like this?

"ConnectionStrings": {
    "ConnectionStringFromAppSettings": "your_connection_string"
  }

Configuration.GetConnectionString always search for the section "ConnectionStrings"

https://docs.microsoft.com/it-it/dotnet/api/microsoft.extensions.configuration.configurationextensions.getconnectionstring?view=dotnet-plat-ext-3.1

Pass connection string to .Net Core EF library from another library

1 Answers