C# 从对象中的内部联接对象中放入值

我有以下带有内部联接的sql命令：

SqlCommand cmd = new SqlCommand(@"SELECT c.comment_Id, c.date, c.comment, c.rating, a.registration_Date, a.username, a.email, a.profile_Image FROM News_comments c INNER JOIN News_accounts a ON c.account_Id=a.account_Id WHERE c.news_Id = @news_Id", conn);
cmd.Parameters.Add("news_Id", SqlDbType.Int).Value = news_Id;
conn.Open();

我想把a（News_accounts）中的值放在对象帐户中，对象帐户本身就在对象newsComment中，对象newsComment位于通用列表List newsComments中。 我是这样做的：

using (SqlDataReader reader = cmd.ExecuteReader()) {                
    while (reader.Read()) {
        Comments newsComment = new Comments();
        newsComment.comment_Id = int.Parse(reader["comment_Id"].ToString());
        newsComment.date = DateTime.Parse(reader["date"].ToString());
        newsComment.comment = reader["comment"].ToString();
        newsComment.rating = int.Parse(reader["rating"].ToString());
        newsComment.account.Registration_Date = DateTime.Parse(reader["registration_Date"].ToString());
        newsComment.account.Username = reader["username"].ToString();
        newsComment.account.Email = reader["email"].ToString();
        newsComment.account.Profile_Image = reader["profile_Image"].ToString();
        newsComments.Add(newsComment);
    }
    return newsComments;
}

newsComment.account = new Account();
newsComment.account.Registration_Date = DateTime.Parse(reader["registration_Date"].ToString());
newsComment.account.Username = reader["username"].ToString();
newsComment.account.Email = reader["email"].ToString();
newsComment.account.Profile_Image = reader["profile_Image"].ToString();

注释有一个构造函数：

public Comments(int comment_Id, DateTime date, string comment, int rating, Accounts account) {
    this.comment_Id = comment_Id;
    this.date = date;
    this.comment = comment;
    this.rating = rating;
    this.account = account;
}

以及账户：

public Accounts(int account_Id, DateTime registration_Date, string email, string username, string profile_Image, string homepage, string about, bool admin) {
    this.account_Id = account_Id;
    this.registration_Date = registration_Date;
    this.email = email;
    this.profile_Image = profile_Image;
    this.homepage = homepage;
    this.about = about;
    this.admin = admin;
}

但是，在评级顺利且值被放入newsComment对象之前，当它达到需要放入对象newsComment中的对象帐户的值时，它会给出一个NullReferenceException。 我知道这意味着它没有价值，但我似乎无法找到它没有价值的原因

我已经用SQLServer2008查询设计器检查了我的内部连接，这很有效 所以它一定是物体，但我看不出问题所在

请帮帮我：）

---

问候语

您没有实例化您的帐户对象，因此它为空

newsComment。帐户

您必须在访问其字段、属性或方法之前初始化该对象。大概是这样的：

using (SqlDataReader reader = cmd.ExecuteReader()) {                
    while (reader.Read()) {
        Comments newsComment = new Comments();
        newsComment.comment_Id = int.Parse(reader["comment_Id"].ToString());
        newsComment.date = DateTime.Parse(reader["date"].ToString());
        newsComment.comment = reader["comment"].ToString();
        newsComment.rating = int.Parse(reader["rating"].ToString());
        newsComment.account.Registration_Date = DateTime.Parse(reader["registration_Date"].ToString());
        newsComment.account.Username = reader["username"].ToString();
        newsComment.account.Email = reader["email"].ToString();
        newsComment.account.Profile_Image = reader["profile_Image"].ToString();
        newsComments.Add(newsComment);
    }
    return newsComments;
}

newsComment.account = new Account();
newsComment.account.Registration_Date = DateTime.Parse(reader["registration_Date"].ToString());
newsComment.account.Username = reader["username"].ToString();
newsComment.account.Email = reader["email"].ToString();
newsComment.account.Profile_Image = reader["profile_Image"].ToString();

。。。也可以从

Comments

类的构造函数中执行，该类不带参数

---

作为一个旁注：也许你应该考虑使用ORM，比如LINQ to SQL或实体框架。这就是他们所做的。

你的意思是我需要放：newcomment.account=newaccounts（）；之后：Comments newsComment=新注释（）？编辑：是的，就是这样。是的，如果它有一个默认的构造函数，它是一个学校项目，对于这个项目，我们还不允许使用LINQ；）