Unable to create database in PostreSQL using Npgsql and Entity Framework code first

Not surprisingly, since your database withoomph is not created yet, you should not able to use connection string where Database=withoomph; is mentioned.

What you can do is to either create this database manually using createdb or psql, or change your connection string temporarily to use Database=postgres; instead.

This should work because on all recent PostgreSQL versions database postgres is guaranteed to exist after vanilla install and should be used just for this purpose - to get initial authenticated connection to create another database and issue CREATE DATABASE withoomph; within your application.

However, after your new database is created, you should immediately disconnect from postgres, connect to new withoomph and continue normally.

In addition to mvp's answer, here's a code snippet I used to create the database. You need to run it before initializing EF. So, the trick is to switch the database name temporarily to 'postgres', which is guaranteed to exists after a vanilla install.

public void CreateDatabase(string connectionString)
{
    var builder = new NpgsqlConnectionStringBuilder(connectionString);
    var databaseName = builder.Database; // REMEMBER ORIGINAL DB NAME
    builder.Database = "postgres"; // TEMPORARILY USE POSTGRES DATABASE

    // Create connection to database server
    using (var connection = new NpgsqlConnection(builder.ConnectionString))
    {
        connection.Open();

        // Create database
        var createCommand = connection.CreateCommand();
        createCommand.CommandText = string.Format(@"CREATE DATABASE ""{0}"" ENCODING = 'UTF8'", databaseName);
        createCommand.ExecuteNonQuery();

        connection.Close();
    }
}