从 SQL 查询设置对象值

Posted 2023-05-08

【中文标题】从 SQL 查询设置对象值

【英文标题】：Setting Object values from SQL Query

【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。

【参考方案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;
            
        
    

【参考方案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。