dbContext.cs

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

public MyDbContext(DbContextOptions<MyDbContext> options) : base(options) { }

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    if (optionsBuilder.IsConfigured == false)
    {
        optionsBuilder
            .UseMySql(_connectionString)
            .ConfigureWarnings(warnings => warnings.Throw(RelationalEventId.QueryClientEvaluationWarning));    
    }
}