How to feed data table from xml file received from Web API? - ado.net

Question

My Web API returns a string looking like XML file below. I put all rows ending with \r\n to new line for readability.
{"DataTable.RemotingVersion":{"major":2,"minor":0,"build":-1,"revision":-1,"majorRevision":-1,"minorRevision":-1},"XmlSchema":" <?xml version=\"1.0\" encoding=\"utf-16\"?>\r\n
<xs:schema xmlns=\"\" xmlns:xs=\"http://www.w3.org/2001/XMLSchema\" xmlns:msdata=\"urn:schemas-microsoft-com:xml-msdata\">\r\n
<xs:element name=\"Test\">\r\n
<xs:complexType>\r\n
<xs:sequence>\r\n
<xs:element name=\"Col1\" type=\"xs:string\" msdata:targetNamespace=\"\" minOccurs=\"0\" />\r\n
<xs:element name=\"Col2\" type=\"xs:string\" msdata:targetNamespace=\"\" minOccurs=\"0\" />\r\n
</xs:sequence>\r\n
</xs:complexType>\r\n
</xs:element>\r\n
<xs:element name=\"tmpDataSet\" msdata:IsDataSet=\"true\" msdata:MainDataTable=\"Test\" msdata:UseCurrentLocale=\"true\">\r\n
<xs:complexType>\r\n
<xs:choice minOccurs=\"0\" maxOccurs=\"unbounded\" />\r\n
</xs:complexType>\r\n
</xs:element>\r\n
</xs:schema>","XmlDiffGram":"<diffgr:diffgram xmlns:msdata=\"urn:schemas-microsoft-com:xml-msdata\" xmlns:diffgr=\"urn:schemas-microsoft-com:xml-diffgram-v1\">\r\n
<tmpDataSet>\r\n
<Test diffgr:id=\"Test1\" msdata:rowOrder=\"0\">\r\n
<Col1>Column 1 value</Col1>\r\n
<Col2>Column 2 value</Col2>\r\n
</Test>\r\n
</tmpDataSet>\r\n
</diffgr:diffgram>"}
I wonder how I can feed this string to a datatable? I tried to feed the table like this
System.Data.DataTable dt = new System.Data.DataTable();
byte[] byteArray =Encoding.ASCII.GetBytes(<above string returned by Web API>);
MemoryStream stream = new MemoryStream( byteArray );
dt.ReadXml(stream);
However, the code failed with exception
System.Xml.XmlException: 'Data at the root level is invalid, position 1

Answer 1

Actually, your WebAPI didn't respond with a valid XML payload but return a JSON instead :
{
"DataTable.RemotingVersion": {...},
"XmlSchema":"... xml schema string ...",
"XmlDiffGram": " ... xml data string ..."
}
So you can't read the whole string by dt.ReadXml(stream);
Also note that the xml string begins with an empty string. It's better to invoke .Trim() before reading the XML string.
A working demo:
Let's create two helper methods that read the schema & data parts into DataTable:
// read the schema into DataTable
public static void ReadSchema(DataTable dt,string schema)
{
var stream = new MemoryStream();
ReadXMLToMemoryStream(schema, stream);
dt.ReadXmlSchema(stream);
}
// read the data into DataTable
public static void ReadData(DataTable dt,string xml)
{
var stream = new MemoryStream();
ReadXMLToMemoryStream(xml,stream);
dt.ReadXml(stream);
}
// read xml string into MemoryStream
private static void ReadXMLToMemoryStream(string xml, MemoryStream stream)
{
var doc = new XmlDocument();
doc.LoadXml(xml.Trim());
doc.Save(stream);
stream.Position = 0;
}
To fix the issue, we need parse the related json properties (I'm using Newtonsoft.Json) :
byte[] bytes = Encoding.ASCII.GetBytes(strReturnedFromWebApi);
MemoryStream ms = new MemoryStream(bytes);
using(var reader = new JsonTextReader(new StreamReader(ms))){
var json = JToken.Load(reader);
var version= json.SelectToken("$.['DataTable.RemotingVersion']");
var schema = (string)json.SelectToken("$.XmlSchema"); // the schema part
var data = (string)json.SelectToken("$.XmlDiffGram"); // the data part
System.Data.DataTable dt = new System.Data.DataTable();
ReadSchema(dt,schema); // read schema
ReadData(dt,data); // read data
}