internal class DynamicPersonDetails<T>
{
    private Database db;

    public DynamicPersonDetails(Database database)
    {
        this.db= database;
    }

    public DbResult GetByColumnName(string columnName, T value)
    {
        var sql =
            "SELECT * FROM person_detail WHERE "+columnName+"="value.toString();

        return this.db.DoQuery(sql).FetchSingle();
    }
}

public class EmailPersonDetails
{
    private DynamicPersonDetails<string> dpd;

    public EmailPersonDetails(DynamicpersonDetails<string> dpd)
    {
        this.dpd = dpd;
    }

    public DbResult GetPersonDetailsByEmail(string email)
    {
        return this.dpd.GetByColumnName("email", email);
    }
}

public class IdPersonDetails
{
    private DynamicPersonDetails<int> dpd;

    public EmailPersonDetails(DynamicpersonDetails<int> dpd)
    {
        this.dpd = dpd;
    }

    public DbResult GetPersonDetailsById(int id)
    {
        return this.dpd.GetByColumnName("id", id);
    }
}