BaseDbContextFactory.cs

using System;
using System.Globalization;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;
using Microsoft.Extensions.Configuration;

namespace Arena.Utilities
{
    public abstract class BaseDbContextFactory<T> : IDesignTimeDbContextFactory<T> where T : DbContext
    {
        public T CreateDbContext(string[] args)
        {
            var configuration = new ConfigurationBuilder()
              .AddUserSecrets<BaseDbContextFactory<T>>()
              .AddEnvironmentVariables()
              .Build();
            var connectionStringTemplate = configuration["Database:ConnectionStringTemplate"];
            if (connectionStringTemplate == null)
            {
                throw new Exception("No Database:ConnectionStringTemplate specified.  Add it to the environment variables or the user secrets for the utilities project");
            }
            var connectionString = string.Format(CultureInfo.InvariantCulture, connectionStringTemplate, GetDbName());
            var optionsBuilder = new DbContextOptionsBuilder<T>();
            optionsBuilder
              .UseNpgsql(connectionString);
            return CreateDbContext(optionsBuilder.Options);
        }

        protected abstract T CreateDbContext(DbContextOptions<T> options);
        protected abstract string GetDbName();
    }
}