public class UserType

{

    public Int32 Id { get; set; }

    public string TypeName { get; set; }

}

public class UserInfo

{

    public Int32 Id { get; set; }

    public string Name { get; set; }

    public string Gender { get; set; }

    public UserType UserType { get; set; } 

}

public IList<UserInfo> GetAllUser()

{

    IList<UserInfo> list = new List<UserInfo>();

    using (SqlConnection conn = new SqlConnection(connectionString))

    {

        conn.Open();

        using (SqlCommand cmd = conn.CreateCommand())

        {

            cmd.CommandText = "select * from UserInfo";

            SqlDataReader reader = cmd.ExecuteReader();

            while (reader.Read())

            {

                UserTypeService userTypeService = new UserTypeService();

                UserInfo userInfo = new UserInfo();

                userInfo.Id = (Int32)reader["Id"];

                userInfo.Name = (string)reader["Name"];

                userInfo.Gender = (string)reader["Gender"];

                userInfo.UserType = userTypeService.GetUserTypeById((Int32)reader["TypeId"]);//外键的处理

                list.Add(userInfo);

            }

        }