XmlNode null reference in custom configuration file

Question

Hello everyone.
I have a Xml that I use like config file. When I try to get data from the child node of DWDD007 node, I get a NullReferenceException, and I don´t know why, but I can get the innertext from child node of DWDD004. Can you help me? Thanks, and sorry for my bad english.

Xml File:
<?xml version="1.0" encoding="utf-8"?>
<Report>
<DWDD004>
<Database>xxxxx</Database>
</DWDD004>
<DWDD007>
<Database>yyyyy</Database>

</DWDD007>

</Report>

C# Code:

public static string GetValue(string nameOfReport, string node)
{
string data = "";
if (!File.Exists(ConfigurationFile))
{
Console.WriteLine($"El archivo {ConfigurationFile} no existe.");
Environment.Exit(-1);
}
try
{
_doc = new XmlDocument();
_doc.Load(ConfigurationFile);
data = _doc.SelectSingleNode("//"+ nameOfReport +"/"+node).InnerText;
}
catch (Exception ex)
{
Console.WriteLine(ex.InnerException.ToString());
Environment.Exit(-1);
}
return data;
}

Answer 1

Hi @NICOLAS 60S ,

What you need is easy to achieve via LINQ to XML.

I saved your XML into a file on the file system: "e:\Temp\NICOLAS60S-5333.xml".

XML

<?xml version="1.0"?>  
<Report>  
	<DWDD004>  
		<Database>xxxxx</Database>  
	</DWDD004>  
	<DWDD007>  
		<Database>yyyyy</Database>  
	</DWDD007>  
</Report>  

c#

void Main()  
{  
	const string filename = @"e:\Temp\NICOLAS60S-5333.xml";  
	const string nameOfReport = "DWDD004";  
  
	XDocument xdoc = XDocument.Load(filename);  
  
	string Database = xdoc.Descendants(nameOfReport)  
		.Elements("Database")  
		.FirstOrDefault()?.Value;  
		  
	Console.WriteLine($"Database='{Database}'");  
}  

Output

Database='xxxxx'  

Answer 2

Hi.

You can use XDocument class of Xml.Linq namespace to do this.

Here is a code snippet for this:

//I cant use a file. So creating XML as string for the example
var xml = "<Report><DWDD004><Database>xxxxx</Database></DWDD004><DWDD007><Database>yyyyy</Database></DWDD007></Report>";
var xmlReader = new StringReader(xml);

//Use XDocument to load your XML file
var xmlDoc = XDocument.Load(xmlReader);
var reportName = "DWDD007";
var nodeValue = xmlDoc.Document
                              .Element("Report")
                              .Element(reportName)
                              .Element("Database")
                              .Value;

Console.WriteLine(nodeValue);

Having said that - do consider using JSON as a configuration file instead of XML. JSON is becoming the defacto for these kind of things. Even in .NET configuration files are JSON now. System.Text.Json makes it easy to deserialize your JSON to a Object.

Hope this helps.

Answer 3

Have you considered using a json file?

In the code below, if a Database is null it's set to empty which you can check on or set a default database.

Using Json.net NuGet package

public class Report
{
    public string Name { get; set; }
    public string Database { get; set; } = "empty";
}

Main class

public class Reports
{
    public List<Report> List { get; set; }
}

Mocking and reading

public class Mocked
{
    private static string _fileName = "Reports.json";
    public static void Populate()
    {
        Reports reports = new Reports
        {
            List = new List<Report>
            {
                new Report() { Name = "DWDD004", Database = "first database" },
                new Report() { Name = "DWDD007" }
            }
        };

        string output = JsonConvert.SerializeObject(reports, Formatting.Indented);
        File.WriteAllText(_fileName, output);

    }

    public static Reports Load()
    {
        var json = File.ReadAllText(_fileName);
        return JsonConvert.DeserializeObject<Reports>(json);
    }
}

Sample reading

Mocked.Populate();
Reports reports = Mocked.Load();

Console.WriteLine("DWDD004");
var firstReport = reports.List.FirstOrDefault(x => x.Name == "DWDD004");
Console.WriteLine(firstReport.Database == "empty" ? "No database name" : firstReport.Database);

Console.WriteLine();

Console.WriteLine("DWDD007");
var secondReport = reports.List.FirstOrDefault(x => x.Name == "DWDD007");
Console.WriteLine(secondReport.Database == "empty" ? "No database name" : secondReport.Database);

Json file created above

{
  "List": [
    {
      "Name": "DWDD004",
      "Database": "first database"
    },
    {
      "Name": "DWDD007",
      "Database": "empty"
    }
  ]
}