CS-Script调用后DataTable丢失列与行的问题求助

问题描述 #

C#应用调用CS-Script方法时，传入包含DataTable X的DataSet。脚本内新建DataTable Y并加入DataSet，调用DataTable.Copy()将X复制到Y，脚本内验证Y有6列约2000行，但返回C#程序后，Y仍存在却无列和行。其他修改DataSet中DataTable的脚本可正常返回结果，求问原因。

脚本代码 #

using System;
using System.Data;
using System.IO;
using CSScript_Types;
using System.Windows.Forms;
using InSight;

//  This is the class that does the Real work of the CS Script After Query work
public class AfterTableScripts : iAfterTableStuff
{
    // This is the generic routine that is called from InSights Into Data
    // Return value is string so that we can handle Bool, string, number, etc. 
    public CSScriptReturnValueClass AfterTableProcess(DataSet CurrDataSet, string CurrTableName, Form_InSightsMain MainForm)
    {
        CSScriptReturnValueClass ReturnRec = new CSScriptReturnValueClass();
        try
        {
            // Here is the code to be run after the Table is created in the dataset
            DataTable QHRInvoices = CurrDataSet.Tables["QHRInvoices"];
            DataTable DupTable = CurrDataSet.Tables.Add("DupsTable");
            DupTable = QHRInvoices.Copy();
            DupTable.TableName = "DupsTable";
            
            // Now Setup the Return Value 
            ReturnRec.Success = true;
            ReturnRec.ReturnValue = "";
            ReturnRec.ErrorMsg = "";
        }
        catch (Exception Ex)
        {
            // Now Setup the Return Value 
            ReturnRec.Success = false;
            ReturnRec.ReturnValue = "";
            ReturnRec.ErrorMsg = Ex.Message;
        }
        return ReturnRec;
    }
}

C#调用代码 #

CSScriptReturnValueClass ReturnValue = new CSScriptReturnValueClass();
//string ReturnValue;
dynamic AfterTableScript = CSScript.Evaluator.LoadCode(CurrCode);
ReturnValue = AfterTableScript.AfterTableProcess(CurrDataSet, CurrTableName, MainForm);

if (ReturnValue.Success)
{
    return true;
}
else
{
    // Need to Change this to a Logging routine
    FlexibleMessageBox.Show("Failure of CS Script:   Error: " + ReturnValue.ErrorMsg, "CodeRunAfterQuery - Message");
    return false;
}

原因分析 #

核心问题出在**DataTable.Copy()的使用逻辑**和DataSet中DataTable的引用关系：

1. 执行DataTable DupTable = CurrDataSet.Tables.Add("DupsTable");时，已经在DataSet中创建了一个空的DataTable实例，DupTable此时指向这个实例。
2. 随后执行DupTable = QHRInvoices.Copy();，DupTable被重新赋值为Copy()返回的新DataTable实例——这个新实例并未被添加到DataSet中。
3. 脚本内验证时，你检查的是这个新的DupTable实例（有数据），但DataSet中实际存在的还是最初创建的空表。返回主程序后，主程序访问的是DataSet里的空表，自然看不到列和行。

解决方案 #

有两种可行的修正方式：

方式一：直接添加复制后的表到DataSet #

去掉先创建空表的步骤，直接将Copy()的结果加入DataSet：

DataTable QHRInvoices = CurrDataSet.Tables["QHRInvoices"];
DataTable DupTable = QHRInvoices.Copy();
DupTable.TableName = "DupsTable";
CurrDataSet.Tables.Add(DupTable); // 直接添加带数据的表

方式二：填充已加入DataSet的空表 #

如果需要保留先创建表的逻辑，不要重新赋值，而是用Clone()复制结构后导入数据，或直接用Merge()：

DataTable QHRInvoices = CurrDataSet.Tables["QHRInvoices"];
DataTable DupTable = CurrDataSet.Tables.Add("DupsTable");
// 复制表结构
DupTable = QHRInvoices.Clone();
// 导入所有行
foreach (DataRow row in QHRInvoices.Rows)
{
    DupTable.ImportRow(row);
}
// 或用Merge更简洁
// DupTable.Merge(QHRInvoices);

内容的提问来源于stack exchange，提问作者G Bradley MacDonald