Unidev Tech Blog

Posts Tagged ‘XML’

by Allan Sieker

When it comes time to write an interesting article about a technical topic my mind goes into a deadlock in trying to find the balance between space/time constraints and keeping the content interesting.  Too short of an article and it seems trivial because the technical stuff doesn’t get covered enough.  Too technical, and the article becomes long and boring.  All the while, wanting to keep things original, informative, and light.  So did I end up with?  How about a series of related articles that covers something that is near and dear to all of us?   

 I bought my first computer in 1978 (yes, I still have it) and as my home network expanded to what it is now – several servers, workstations, and laptops, the need for keeping a file inventory goes with the territory.  Sure, over the years I created my own file databases written in several languages (BASIC, Pascal, dBASE, Clipper, VB, C#) and they all served their purpose, but technology keeps improving and I always want more.   

 What if data warehousing concepts were applied to capture the “slowly changing dimension” of file updates?  What if file collections were recognized and managed as applications and other entities?  What if all of the computer file inventories were gathered locally then stored centrally for searches via a web interface?   What if backup history were also available?

 This article series will cover a broad range of technical topics with the end goal being a respectable system for home or business usage.  Concepts will be discussed and code will be available for download.  References to other articles and postings will also be made.

 Here is a brief list of planned topics: 

• Using recursive methods to collect file information from all of the folders on a drive.
• Creating console and Windows “file agent” applications to collect file data and write to an XML file.
• Creating a SQL Server file inventory database.
• Balancing cost and architecture to avoid over-costing and over-engineering.
• Importing “file agent” XML into the database.
• Creating an ASP.NET web application for searching and retrieving application & file information.
• Making “file agent” applications downloadable from the web site using ClickOnce.
• Using the Visual Studio Report Designer and the ReportViewer control to create web reports.
• Creating a “wrapper” application for Microsoft’s Backup to manage and track backups.
• Detecting media and image file duplicates based on file content instead of file name.

 Feedback is always welcome.

By George Zheng

XML has been used in a lot of places for transferring data because of its platform independence and its simple, text-based, self-describing format. It is a common requirement for preparing and consuming XML data. Microsoft provides several convenience tools to help developers deal with XML under .NET platform.

1. System.Xml.XmlTextReader/System.Xml.XmlTextWriter
2. System.Xml.Serialization.XMLSerializer
3. System.Xml.Linq

XmlTextReader/XmlTextWriter
XmlDocument objects are easy to use for navigating the DOM copying, modifying, or inserting nodes. However, they can also use a large amount of memory to store the entire DOM of a large XML string in memory. Because of this, the XmlTextReader and XmlTextWriter classes can be used for stream based manipulation of an XML string.
Let’s say you have an XML as:
<?xml version=“1.0“ encoding=“utf-8“ ?>
<user id=“1“>
<firstname>George</firstname>
<lastname>Zheng</lastname>
</user>

Following code will read it into a user object.

User user = new User();
XmlTextReader reader = new XmlTextReader(“user.xml”);

while (reader.Read())
{
if (reader.NodeType == XmlNodeType.Element)
{
if (reader.Name == “user”)
{
user.Id = Convert.ToInt32(reader.GetAttribute(“id”));
}
if (reader.Name == “firstname”)
{
user.Firstname = reader.ReadElementContentAsString();
}
if (reader.Name == “lastname”)
{
user.Lastname = reader.ReadElementContentAsString();
}
}
}
With XmlTextWriter, following code will generate XML string:

StringBuilder sb = new StringBuilder();
StringWriter sw = new StringWriter(sb);
XmlTextWriter writer = new XmlTextWriter(sw);

writer.WriteStartElement(“user”);
writer.WriteAttributeString(“id”, user.Id.ToString());
writer.WriteElementString(“firstname”, user.Firstname);
writer.WriteElementString(“lastname”, user.Lastname);
writer.WriteEndElement();

return sb.ToString();

XMLSerializer

If you don’t want to deal with the XML element by element, .NET provides an alternative approach to convert object instance to XML and read the data back – XML Serialization. This is more convenience for a complex object.

TextReader tr = new StringReader(xml);
XmlSerializer s = new XmlSerializer(typeof(User));
User user = (User)s.Deserialize(tr);

Following code can be used to serialize the object:

XmlSerializer s = new XmlSerializer(typeof(User));
TextWriter writer = new StringWriter();
s.Serialize(writer, user);
writer.Flush();
string xml = writer.ToString();
writer.Close();

The object can be a complex object like:

public class User
{
[XmlAttribute("id")]
public int Id { get; set; }

[XmlElement("firstname")]
public string Firstname { get; set; }
[XmlElement("lastname")]
public string Lastname { get; set; }

[XmlArray("projects")]
[XmlArrayItem("project", typeof(Project))]
public List<Project> Projects { get; set; }
}

public class Project
{
[XmlAttribute("id")]
public int Id { get; set; }
[XmlElement("name")]
public string Name { get; set; }
}

As you can see, serializer attributes can be used to specify how the object’s properties map to XML entities. I’m not going to discuss these attributes here. Details can be found from Useful Links below.

LINQ

In some case, convert the whole XML may not be a good idea. Linq provides a convenience approach to query a complex XML.

Here is the example account feed response from Google Analytics API

<?xml version=‘1.0‘ encoding=‘UTF-8‘?>
<feed xmlns=‘http://www.w3.org/2005/Atom‘ xmlns:openSearch=‘http://a9.com/-/spec/opensearchrss/1.0/‘ xmlns:dxp=‘http://schemas.google.com/analytics/2009‘>
<id>http://www.google.com/analytics/feeds/accounts/abc@test.com</id>
<updated>2009-06-25T03:55:22.000-07:00</updated>
<title type=‘text‘>Profile list for abc@test.com</title>
<link rel=‘self‘ type=‘application/atom+xml‘ href=‘http://www.google.com/analytics/feeds/accounts/default‘/>
<author>
<name>Google Analytics</name>
</author>
<generator version=‘1.0‘>Google Analytics</generator>
<openSearch:totalResults>12</openSearch:totalResults>
<openSearch:startIndex>1</openSearch:startIndex>
<openSearch:itemsPerPage>12</openSearch:itemsPerPage>
<entry>
<id>http://www.google.com/analytics/feeds/accounts/ga:1174</id>
<updated>2009-06-25T03:55:22.000-07:00</updated>
<title type=‘text‘>www.googlestore.com</title>
<link rel=‘alternate‘ type=‘text/html‘ href=‘http://www.google.com/analytics‘/>
<dxp:tableId>ga:1174</dxp:tableId>
<dxp:property name=‘ga:accountId‘ value=‘30481‘/>
<dxp:property name=‘ga:accountName‘ value=‘Google Store‘/>
<dxp:property name=‘ga:profileId‘ value=‘1174‘/>
<dxp:property name=‘ga:webPropertyId‘ value=‘UA-30481-1‘/>
<dxp:property name=‘ga:currency‘ value=‘USD‘/>
<dxp:property name=‘ga:timezone‘ value=‘America/Los_Angeles‘/>
</entry>
<entry>
<id>http://www.google.com/analytics/feeds/accounts/ga:6284812</id>
<updated>2009-01-06T17:39:33.000-08:00</updated>
<title type=‘text‘>www.googlestore.com (Test Team)</title>
<link rel=‘alternate‘ type=‘text/html‘ href=‘http://www.google.com/analytics‘/>
<dxp:tableId>ga:6284812</dxp:tableId>
<dxp:property name=‘ga:accountId‘ value=‘30481‘/>
<dxp:property name=‘ga:accountName‘ value=‘Google Store‘/>
<dxp:property name=‘ga:profileId‘ value=‘6284812‘/>
<dxp:property name=‘ga:webPropertyId‘ value=‘UA-30481-1‘/>
<dxp:property name=‘ga:currency‘ value=‘USD‘/>
<dxp:property name=‘ga:timezone‘ value=‘America/Los_Angeles‘/>
</entry>
</feed>

With following code, you will get ID, Title and AccountName for each entry.

XDocument doc = XDocument.Parse(xml);
XNamespace dxpSpace = doc.Root.GetNamespaceOfPrefix(“dxp”);
XNamespace defaultSpace = doc.Root.GetDefaultNamespace();

IEnumerable<Account> entries =
from en in doc.Root.Descendants(defaultSpace + “entry”)
select new Account
{
ID = en.Element(defaultSpace + “id”).Value,
Title = en.Element(defaultSpace + “title”).Value,
AccountName =
en.Elements(dxpSpace + “property”).Where(
xe => xe.Attribute(“name”).Value == “ga:accountName”).First().
Attribute(“value”).Value
};

Useful Links

Insert XML Nodes Using XmlTextReader and XmlTextWriter
Using the XmlSerializer Attributes
Added Google Analytics Reader for .NET


Download source code