dataSet.GetXml() 不会为空列或空白列返回 xml

Question

当我调用 dataSet.GetXml() 时，我没有为具有空值或空值的列返回任何 xml。有没有一种简单有效的方法来解决这个问题？以下问题的示例。注意第二个结果部分是如何缺少 a2 的。

<results>
<a1>test1</a1>
<a2>test2</a2>
<a3>test3</a3>
</results>
<results>
<a1>Atest1</a1>
<a3>Atest3</a3>
</results>

Answer 1

Microsoft 知识库文章中详细介绍了该问题：http://support.microsoft.com/default.aspx?scid=kb;EN-US;Q317961。有关详细信息，请参阅之前的 SO 问题：DataSet.GetXml not returning null results.

我认为你的直接问题没有很好的解决方案。鉴于上下文，可能还有另一种方法来解决这个问题。

Answer 2

一个对我有用的解决方案。

首先克隆 DataTable，将所有列设为字符串类型，用

string.empty

替换所有空值，然后在新的 DataSet 上调用

GetXml

。

        DataTable dtCloned = dt.Clone();
        foreach (DataColumn dc in dtCloned.Columns)
            dc.DataType = typeof(string);
        foreach (DataRow row in dt.Rows)
        {
            dtCloned.ImportRow(row);
        }

        foreach (DataRow row in dtCloned.Rows)
        {
            for (int i = 0; i < dtCloned.Columns.Count; i++)
            {
                dtCloned.Columns[i].ReadOnly = false;

                if (string.IsNullOrEmpty(row[i].ToString()))
                    row[i] = string.Empty;
            }
        }

        DataSet ds = new DataSet();
        ds.Tables.Add(dtCloned);
        string xml = ds.GetXml();

Answer 3

我一直在全世界寻找使用 DataSet.WriteXML() 将空字段写入 XML 的解决方案。我发现以下以性能优化的方式工作。为了您的方便，我创建了一个函数。通过调用以下函数并替换表，一个接一个地更改数据集表。

    private DataTable GetNullFilledDataTableForXML(DataTable dtSource)
    {
        // Create a target table with same structure as source and fields as strings
        // We can change the column datatype as long as there is no data loaded
        DataTable dtTarget = dtSource.Clone();
        foreach (DataColumn col in dtTarget.Columns)
            col.DataType = typeof(string);

        // Start importing the source into target by ItemArray copying which 
        // is found to be reasonably fast for nulk operations. VS 2015 is reporting
        // 500-525 milliseconds for loading 100,000 records x 10 columns 
        // after null conversion in every cell which may be usable in many
        // circumstances.
        // Machine config: i5 2nd Gen, 8 GB RAM, Windows 7 64bit, VS 2015 Update 1
        int colCountInTarget = dtTarget.Columns.Count;
        foreach (DataRow sourceRow in dtSource.Rows)
        {
            // Get a new row loaded with data from source row
            DataRow targetRow = dtTarget.NewRow();
            targetRow.ItemArray = sourceRow.ItemArray;

            // Update DBNull.Values to empty string in the new (target) row
            // We can safely assign empty string since the target table columns
            // are all of string type
            for (int ctr = 0; ctr < colCountInTarget; ctr++)
                if (targetRow[ctr] == DBNull.Value)
                    targetRow[ctr] = String.Empty;

            // Now add the null filled row to target datatable
            dtTarget.Rows.Add(targetRow);
        }

        // Return the target datatable
        return dtTarget;
    }

Answer 4

            if (ds != null && ds.Tables.Count > 0 && ds.Tables[0].Rows.Count == 0)
            {
                foreach (DataTable dt in ds.Tables)
                {
                    foreach (DataColumn dc in dt.Columns)
                    {
                        dc.DataType = typeof(String);
                    }
                }

                DataRow dr = ds.Tables[0].NewRow();
                for (int i = 0; i < dr.ItemArray.Count(); i++)
                {
                    dr[i] = string.Empty;
                }
                ds.Tables[0].Rows.Add(dr);
            }

Answer 5

  private static string GetNonNullXMLDataFromDataSet(DataSet dsData, string sNullValueReplacementString)
    {
        string xml = "";
        ////xml = dsData.GetXml();
        DataRow drClonned = null;
        DataTable dtCloned = null;

        //////// Make a clone and set all columns as string
        DataSet dsCloned = dsData.Clone();
        foreach (DataTable dt in dsCloned.Tables)
        {
            foreach (DataColumn dc in dt.Columns)
            {
                dc.DataType = typeof(string);
                ////dc.ColumnMapping = MappingType.Attribute;
            }
        }

        //////// Get data from orignal datatable and create new row in cloned table
        //////// replace DBNull.Value with the provided string marker
        foreach (DataTable dt in dsData.Tables)
        {
            dtCloned = dsCloned.Tables[dt.TableName];
            if (dt.Rows.Count > 0)
            {
                foreach (DataRow row in dt.Rows)
                {
                    drClonned = dtCloned.NewRow();
                    foreach (DataColumn dcc in dt.Columns)
                    {
                        if (row[dcc.ColumnName] == DBNull.Value)
                        {
                            drClonned[dcc.ColumnName] = sNullValueReplacementString;
                        }
                        else
                        {
                            drClonned[dcc.ColumnName] = row[dcc.ColumnName].ToString();
                        }
                    }
                    dtCloned.Rows.Add(drClonned);
                }
            }
            else
            {
                drClonned = dtCloned.NewRow();

                foreach (DataColumn dcc in dtCloned.Columns)
                {
                    drClonned[dcc.ColumnName] = sNullValueReplacementString;
                }
                dtCloned.Rows.Add(drClonned);
            }
        }

        xml = dsCloned.GetXml();
        ////StringReader sr = new StringReader(xml);
        ////dsCloned.ReadXml(sr);
        ////xml = dsCloned.GetXml();
        return xml;

    }