Can not read XML data from the file written with 'dataTable.WriteXml()' method

Question

I have a data table with the following columns.

    dataTable.Columns.Add("ID", typeof(string));
    dataTable.Columns.Add("File Name", typeof(string));
    dataTable.Columns.Add("Date Taken", typeof(string));
    dataTable.Columns.Add("Size", typeof(string));
    dataTable.Columns.Add("Unique", typeof(bool));

A data table is written to XML file as follows

if (dgView.DataSource is DataTable dataTable) // Ensure DataSource is a DataTable
{
    if (string.IsNullOrWhiteSpace(dataTable.TableName))
    {
        dataTable.TableName = "MyDataTable"; // Assign a name to avoid serialization error
    }

    string dataTime = DateTime.Now.ToString("yyyy-MM-dd_HH-mm-ss"); // Dynamic timestamp
    string defaultFolder = txtSort.Text.Trim(); // Default folder from txtSort
    string defaultFileName = $"{dataTime}.xml";

    using (SaveFileDialog saveFileDialog = new SaveFileDialog())
    {
        saveFileDialog.InitialDirectory = Directory.Exists(defaultFolder) ? defaultFolder : Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
        saveFileDialog.FileName = defaultFileName;
        saveFileDialog.Filter = "XML Files (*.xml)|*.xml|All Files (*.*)|*.*";
        saveFileDialog.Title = "Save DataTable as XML";

        if (saveFileDialog.ShowDialog() == DialogResult.OK)
        {
            try
            {
                dataTable.WriteXml(saveFileDialog.FileName);
                MessageBox.Show($"Data saved to {saveFileDialog.FileName}", "Data Saved", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
            catch (Exception ex)
            {
                MessageBox.Show($"Error saving data: {ex.Message}", "Save Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
    }
}
else
{
    MessageBox.Show("No valid data table found in DataGridView.", "No Data", MessageBoxButtons.OK, MessageBoxIcon.Warning);
}

The file is created as follows:

<?xml version="1.0" standalone="yes"?>
<DocumentElement>
  <MyDataTable>
    <ID>1</ID>
    <File_x0020_Name>H:\Image backup\TEST_SOURCE\01\IMG_7718(8).jpg</File_x0020_Name>
    <Date_x0020_Taken>Jan/17/2016 14:46:06</Date_x0020_Taken>
    <Size>0.673 MB</Size>
    <Unique>true</Unique>
  </MyDataTable>
  <MyDataTable>
    <ID>2</ID>
    <File_x0020_Name>H:\Image backup\TEST_SOURCE\01\IMG_7718(2).jpg</File_x0020_Name>
    <Date_x0020_Taken>Jan/17/2016 14:46:06</Date_x0020_Taken>
    <Size>0.673 MB</Size>
    <Unique>true</Unique>
  </MyDataTable>
  <MyDataTable>
    <ID>3</ID>
    <File_x0020_Name>H:\Image backup\TEST_SOURCE\01\IMG_7719(3).jpg</File_x0020_Name>
    <Date_x0020_Taken>Jan/17/2016 14:46:07</Date_x0020_Taken>
    <Size>1.045 MB</Size>
    <Unique>true</Unique>
  </MyDataTable>
  <MyDataTable>
    <ID>7</ID>
    <File_x0020_Name>H:\Image backup\TEST_SOURCE\01\IMG_7719(2).jpg</File_x0020_Name>
    <Date_x0020_Taken>Jan/17/2016 14:46:07</Date_x0020_Taken>
    <Size>1.045 MB</Size>
    <Unique>true</Unique>
  </MyDataTable>
</DocumentElement>

When I read the file as follows, no data is read. (NUmber of rows is 0.)

private void btnRetrieve_Click(object sender, EventArgs e)
{
    OpenFileDialog OpenFileDialog = new OpenFileDialog();
    if (OpenFileDialog.ShowDialog() == DialogResult.OK)
    {
        string fileName = OpenFileDialog.FileName;
        Task.Run(() =>
        {
            // Load the data from XML into the DataTable
            DataTable dataTable = new DataTable();
            dataTable.Columns.Add("ID", typeof(string));
            dataTable.Columns.Add("File_x0020_Name", typeof(string)); // Handle space as _x0020_
            dataTable.Columns.Add("Date_x0020_Taken", typeof(string)); // Handle space as _x0020_
            dataTable.Columns.Add("Size", typeof(string));
            dataTable.Columns.Add("Unique", typeof(bool));

            // Read the XML into the DataTable
            if (File.Exists(fileName))
            {
                try
                {
                    dataTable.ReadXml(fileName);

                    // Check if data has been loaded
                    if (dataTable.Rows.Count == 0)
                    {
                        this.Invoke(new Action(() =>
                        {
                            MessageBox.Show("The XML file was loaded, but no data was found.", "Data Load Error", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                        }));
                    }
                    else
                    {
                        // Populate the dictionary with data from the DataTable
                        ConcurrentDictionary<string, List<mediaFile>> g_allFiles = new ConcurrentDictionary<string, List<mediaFile>>();

                        foreach (DataRow row in dataTable.Rows)
                        {
                            mediaFile media = new mediaFile
                            {
                                id = row["ID"].ToString(),
                                fileName = row["File_x0020_Name"].ToString(),
                                exif_date = row["Date_x0020_Taken"].ToString(),
                                fileSize = row["Size"].ToString(),
                                unique = Convert.ToBoolean(row["Unique"])
                            };

                            // Extract the file extension (3 letters)
                            string fileExtension = Path.GetExtension(media.fileName)?.Substring(1, 3).ToLower();

                            if (!string.IsNullOrEmpty(fileExtension))
                            {
                                if (!g_allFiles.ContainsKey(fileExtension))
                                {
                                    g_allFiles[fileExtension] = new List<mediaFile>();
                                }

                                g_allFiles[fileExtension].Add(media);
                            }
                        }

                        dataTable.Columns["File_x0020_Name"].ColumnName = "File Name";
                        dataTable.Columns["Date_x0020_Taken"].ColumnName = "Date Taken";

                        // Update DataGridView with loaded data
                        this.Invoke(new Action(() =>
                        {
                            dgView.DataSource = dataTable;
                        }));
                    }
                }
                catch (Exception ex)
                {
                    // Handle errors in reading the XML
                    this.Invoke(new Action(() =>
                    {
                        MessageBox.Show($"Error reading the XML file: {ex.Message}", "File Read Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    }));
                }
            }
            else
            {
                // If file not found, show a message on the UI thread
                this.Invoke(new Action(() =>
                {
                    MessageBox.Show("The specified file path does not exist.", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }));
            }
        });
    }
    var k = g_allFiles;
}

What am I doing wrong here?

Answer 1

A direct load into the DataTable is not working for your XML file sample. It is erroring out with the following error:

DataTable does not support schema inference from Xml

Please try the following solution that is using DataSet datatype as an intermediate object.

As @jdweng pointed out:

There is no reason to add column manually before reading the xml.

I tested your exact XML file, and it is working.

c#

void Main()
{
    const string xmlFilePath = @"e:\Temp\dataTable.xml";

    DataSet dataSet = new DataSet();

    dataSet.ReadXml(xmlFilePath);
    DataTable dataTable = dataSet.Tables[0];

    // Display the data
    foreach (DataRow row in dataTable.Rows)
    {
        foreach (DataColumn column in dataTable.Columns)
        {
            Console.Write($"{row[column]} ");
        }
        Console.WriteLine();
    }
}

Output

ID	File Name	Date Taken	Size	Unique
1	H:\Image backup\TEST_SOURCE\01\IMG_7718(8).jpg	Jan/17/2016 14:46:06	0.673 MB	true
2	H:\Image backup\TEST_SOURCE\01\IMG_7718(2).jpg	Jan/17/2016 14:46:06	0.673 MB	true
3	H:\Image backup\TEST_SOURCE\01\IMG_7719(3).jpg	Jan/17/2016 14:46:07	1.045 MB	true
7	H:\Image backup\TEST_SOURCE\01\IMG_7719(2).jpg	Jan/17/2016 14:46:07	1.045 MB	true