C# EF Core 6 How do I pass connection string into Context constructor as a string and not as an option

Question

I have a strange requirement here. We have a ton of databases that are basically idential but with different clients. So each db has the same table structures. With that being said, I can't use the standard way of setting up the connectionstring in the startup. I would like to see if there is a way I can pass the connectionstring in the contructor without it being the DbContextOptions<> object. We use to be able to do that in earlier versions of EF but now it's expecting that option in the base().

The other option is just doing raw ADO with a command object, which I REALLY don't want to do, I would prefer if I could use EF.

So this is what it looks like, but would prefer to have a second constructor that allows the connectionString to be passed in. NO Start Up or NO appsettings.json, just want to pass in a string with the connectionString.

`

public  class Context : DbContext
{
    public Context(DbContextOptions<Context> options) : base(options) // <== base expects only options
    {
        Database.SetCommandTimeout(9000);
    }

    public Context(string connectionString) : base()
    {
        this.Database.Connection ????? What to do here
    }
    

    public DbSet<Transcription> Transcriptions { get; set; }


    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        builder.HasDefaultSchema("dbo");

        builder.Entity<Transcription>().ToTable("Transcriptions", "dbo");
    }

}`

Any idea why this keeps throwing errors or why it won't allow me to set the connectionString instead of using options?

I have looked an keep getting old solutions from 12+ years ago, nothing for EF 6

Answer 1

Possibly more convenient would be to use multitenancy approaches described in the docs but if you still want to use just the ctor you can override the OnConfiguring method and use connection string from the ctor there:

public class Context : DbContext
{
    private readonly string _connectionString;

    public Context(string connectionString)
    {
        _connectionString = connectionString;
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        if (!optionsBuilder.IsConfigured)
        {
            // setup options - provider, connection string, etc.
            optionsBuilder.UseNpgsql(_connectionString);
        }
    }
}

Or manually building options from the connection string:

public class Context : DbContext
{
    public Context(string connectionString):base(BuildOpts(connectionString))
    {

    }

    private static DbContextOptions<Context> BuildOpts(string connectionString) =>
        new DbContextOptionsBuilder<Context>()
            .UseNpgsql(connectionString) // setup options - provider, connection string, etc.
            .Options;
}