从 SQL 查询设置对象值答案

【问题标题】：Setting Object values from SQL Query从 SQL 查询设置对象值
【发布时间】：2017-05-25 20:25:09
【问题描述】：

我正在尝试遍历 SQL 查询并将对象参数设置为特定值。似乎工作正常的唯一值是 workpack.JobCardIDs，因为我可以实现一个 foreach 循环来显示结果。例如，如果我尝试将 Label 的 Text 属性设置为 workpack.WorkPackTitle，即使数据库值是每一行的值，它也会显示空白。

我对 OOP 还很陌生，所以不能完全确定我是否遗漏了一些基本的东西。

    public class WorkPack
    {
        public int ID { get; set; }
        public string WorkPackNumber { get; set; }
        public string WorkPackTitle { get; set; }
        public string WorkPackDescription { get; set; }
        public Boolean IFC { get; set; }
        public string SPA { get; set; }
        public string Writer { get; set; }
        public string Organization { get; set; }
        public List<int> JobCardIDs { get; set; }
        public int JobCard { get; set; }
    }

    public static WorkPack PopulateWorkPackObject(WorkPack workpack, int workPackID)
    {
        string ConnectionString = ConfigurationManager.ConnectionStrings["vmdatamanagerConnectionString"].ConnectionString;
        string sqlCall = "I HAVE REMOVED CALL BUT VERIFIED IT FUNCTIONS (SELECT columns FROM workpackdatabase where workpackname = x";

        using (SqlConnection con = new SqlConnection(ConnectionString))
        {
            using (SqlCommand cmd = new SqlCommand(sqlCall, con))
            {
                cmd.Connection.Open();
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        if (reader.IsDBNull(reader.GetOrdinal("PARAM1")) == false)
                            workpack.WorkPackNumber = (reader.GetString(reader.GetOrdinal("PARAM1")));

                        if (reader.IsDBNull(reader.GetOrdinal("PARAM2")) == false)
                            workpack.WorkPackTitle = reader.GetString(reader.GetOrdinal("PARAM2"));

                        if (reader.IsDBNull(reader.GetOrdinal("PARAM3")) == false)
                            workpack.WorkPackDescription = reader.GetString(reader.GetOrdinal("PARAM3"));

                        if (reader.IsDBNull(reader.GetOrdinal("PARAM4")) == false)
                            workpack.IFC = reader.GetBoolean(reader.GetOrdinal("PARAM4"));

                        if (reader.IsDBNull(reader.GetOrdinal("PARAM5")) == false)
                            workpack.SPA = reader.GetString(reader.GetOrdinal("PARAM5"));

                        if (reader.IsDBNull(reader.GetOrdinal("PARAM6")) == false)
                            workpack.Writer = reader.GetString(reader.GetOrdinal("PARAM6"));

                        if (reader.IsDBNull(reader.GetOrdinal("PARAM7")) == false)
                            workpack.Organization = reader.GetString(reader.GetOrdinal("PARAM7"));

                        if (reader.IsDBNull(reader.GetOrdinal("PARAM8")) == false)
                            jobCardIDs.Add(reader.GetInt32(reader.GetOrdinal("PARAM8")));

                    }
                    workpack.JobCardIDs = jobCardIDs;
                    return workpack;
                }
            }
        }
    }

【问题讨论】：

如果在 while(reader.Read()) 行上设置断点，它会进入循环还是完全跳过循环？
它进入循环内部，遍历循环并将记录添加到 jobCardIDs 列表。然后，当在方法之外我可以调用 workpack.JobCardIDs 并且可以读取它。工作包对象的所有其他元素都是空白的。这是一个奇怪的。

标签： sql asp.net sql-server class object

【解决方案1】：

看起来您从未创建 jobCardIDs 列表的本地实例。您需要在 ExecuteReader 块内执行此操作。见下文。总账

public static WorkPack PopulateWorkPackObject(WorkPack workpack, int workPackID)
{
    string ConnectionString = ConfigurationManager.ConnectionStrings["vmdatamanagerConnectionString"].ConnectionString;
    string sqlCall = "I HAVE REMOVED CALL BUT VERIFIED IT FUNCTIONS (SELECT columns FROM workpackdatabase where workpackname = x";

    using (SqlConnection con = new SqlConnection(ConnectionString))
    {
        using (SqlCommand cmd = new SqlCommand(sqlCall, con))
        {
            cmd.Connection.Open();
            using (SqlDataReader reader = cmd.ExecuteReader())
            {
                List<int> jobCardIDs = new List<int>(); //<--***THIS IS THE LINE YOU NEED TO ADD***
                while (reader.Read())
                {
                    if (reader.IsDBNull(reader.GetOrdinal("PARAM1")) == false)
                        workpack.WorkPackNumber = (reader.GetString(reader.GetOrdinal("PARAM1")));

                    if (reader.IsDBNull(reader.GetOrdinal("PARAM2")) == false)
                        workpack.WorkPackTitle = reader.GetString(reader.GetOrdinal("PARAM2"));

                    if (reader.IsDBNull(reader.GetOrdinal("PARAM3")) == false)
                        workpack.WorkPackDescription = reader.GetString(reader.GetOrdinal("PARAM3"));

                    if (reader.IsDBNull(reader.GetOrdinal("PARAM4")) == false)
                        workpack.IFC = reader.GetBoolean(reader.GetOrdinal("PARAM4"));

                    if (reader.IsDBNull(reader.GetOrdinal("PARAM5")) == false)
                        workpack.SPA = reader.GetString(reader.GetOrdinal("PARAM5"));

                    if (reader.IsDBNull(reader.GetOrdinal("PARAM6")) == false)
                        workpack.Writer = reader.GetString(reader.GetOrdinal("PARAM6"));

                    if (reader.IsDBNull(reader.GetOrdinal("PARAM7")) == false)
                        workpack.Organization = reader.GetString(reader.GetOrdinal("PARAM7"));

                    if (reader.IsDBNull(reader.GetOrdinal("PARAM8")) == false)
                        jobCardIDs.Add(reader.GetInt32(reader.GetOrdinal("PARAM8")));

                }
                workpack.JobCardIDs = jobCardIDs;
                return workpack;
            }
        }
    }
}

【讨论】：

【解决方案2】：

社区之前给出的答案并没有解决问题，尽管我确实添加了额外的 sn-p 。

问题在于创建对象并在回传之间传递。该对象将与选择作业卡选项卡相关，但一旦加载页面，就没有代码来重建该实例。

添加

      Object foo = new Object();

在 page_Load() 中并重建解决了该问题。如果有人对如何让实例保持活力有任何建议，我完全赞成。我认为 ViewState() 和 Session[] 都是适用的方法。

【讨论】：