NewRow fails when using XML document as Dataset

[Piyush Gupta]

Hi All,

I am using following code snippet to add another user in Users.xml:
-------------------------------------------------------------------
DataSet dstUsers = new DataSet();
dstUsers.ReadXml("Users.xml");
DataTable dtbUsers = dstUsers.Tables["User"];
DataRow drwUser = dtbUsers.NewRow();
drwUser["UserName"] = "Test User 2";
dtbUsers.Rows.Add(drwUser);
dstUsers.WriteXml("Users.xml");
-------------------------------------------------------------------
Users.xml looks like
-------------------------------------------------------------------
<?xml version="1.0" standalone="yes"?>
<Configuration>
<Users>
<User>
<UserName>Test User</UserName>
</User>
</Users>
<Roles>
<Role>
<RoleName>Test Role</RoleName>
</Role>
</Roles>
</Configuration>
-------------------------------------------------------------------

After execution of code, <User> tag is inserted at wrong position and
Users.xml looks like:
-------------------------------------------------------------------
<?xml version="1.0" standalone="yes"?>
<Configuration>
<Users>
<User>
<UserName>Test User</UserName>
</User>
</Users>
<User>
<UserName>Test User 2</UserName>
</User>
<Roles>
<Role>
<RoleName>Test Role</RoleName>
</Role>
</Roles>
</Configuration>
-------------------------------------------------------------------

But if I modify Users.xml as below, <User> tag is inserted at proper
position.
-------------------------------------------------------------------
<?xml version="1.0" standalone="yes"?>
<Users>
<User>
<UserName>Test User</UserName>
</User>
</Users>
-------------------------------------------------------------------

Can anyone give any idea that how can I insert <User> tag inside
<Users> tag without modifying XML format like above???

[Derek Harmon]

"Piyush Gupta" <pi*******@gmail.com> wrote in message news:f6**************************@posting.google.c om...

Can anyone give any idea that how can I insert <User> tag inside
<Users> tag without modifying XML format like above???
What you probably think you're seeing when you look at
the XML fragment,

: : <Users>
<User>
<UserName>Test User</UserName>
</User>
</Users>
is one DataTable named "User," based on the simple
statements you've used to add a row to this table,

: : DataTable dtbUsers = dstUsers.Tables["User"];
DataRow drwUser = dtbUsers.NewRow();
drwUser["UserName"] = "Test User 2";
dtbUsers.Rows.Add(drwUser);
but this appearance can, perhaps, be misleading.

Actually, there are 2 DataTables in the above XML
fragment, and no less than 3 DataColumns (not one).
If you read the DataRow in dstUsers.Tables["User"]
to begin with, you'll see two of these DataColumns,
the "UserName" column and the "Users_Id" 'foreign
key' column that relates the "User" child DataTable
to it's "Users" parent DataTable.

: : <Users>
<User>
<UserName>Test User</UserName>
</User>
</Users>
<User>
<UserName>Test User 2</UserName>
</User>

The <User> record here appears outside of a <Users>
container because when adding a new DataRow you've
specified no value for the Users_Id column that
tells the DataSet which <Users> container element
that <User> record belongs to. Since it's value
for Users_Id is 'null', it appears outside of any
containing <Users> element.

The corrected code would look like this,

DataTable dtbUsers = dstUsers.Tables[ "User"];
DataRow drwUser = dtbUsers.NewRow( );
drwUser[ "UserName"] = "Test User 2";
drwUser[ "Users_Id"] = 0; // Put under first <Users> element.
dtbUsers.Rows.Add( drwUser);

If the XML document you're working with isn't truly a
relational data set, then using DataSet to manipulate
that document should be discouraged. You'll have a
much easier time working directly with an XmlDocument,
instead:

// Create and load XmlDocument
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load( "Users.xml");

// Position yourself where you want to insert new elements.
XmlNode eUsers = xmlDoc.DocumentElement.FirstChild;

// Create <User>/<UserName>/#text.
XmlElement eUserNew = xmlDoc.CreateElement( "User");
XmlElement eUserNameNew = xmlDoc.CreateElement( "UserName");
XmlText txUserNameNew = xmlDoc.CreateTextNode( "Test User 2");

// Connect the XmlNodes you've just created.
eUserNameNew.AppendChild( txUserNameNew);
eUserNew.AppendChild( eUserNameNew);
eUsers.AppendChild( eUserNew);

The XmlDocument will hold an open file handle when you call
Load() with the filename string, so it's usually best to
cons'up an XmlTextReader to load the file (then close the
XmlTextReader after the load operation has completed) and
use an XmlTextWriter to save the file.

However, you never have to guess what your data model is,
as when trying to shove these manipulations through the
DataSet API (which is really intended for other purposes.)
Derek Harmon