Sushil's WebLog : SQL Server's Xml DataType w/ADO.Net 2.0

Typed XML in ADO.Net v2.0

sushilc — Wed, 04 Aug 2004 20:38:00 GMT

In the earlier sections, we have been looking at Untyped XML which are different from Typed XML. Typed XML data type is an XML defined with an associated xml schema in Sql Server 2005. You may ask if there is anything different on how Typed XML are exposed via ADO.Net 2.0. The answer is a heart-warming NO!. Typed XML are exposed the same way that any untyped XML does through SqlDataReader and SqlParameter. Please note that the check to see if the given XML adheres to the give schema is not done on the client side. This check is done when the statement is executed on the server side.

There are new set of columns added to the DataTable returned from SqlDataReader.GetSchemaTable() method that give extra information pertaining to the associated XML Schema. The three columns that are added are:

XmlSchemaCollectionDatabase:Provides the database in which the schema for this XML type exists.
XmlSchemaCollectionOwningSchema:Provides the owning relational schema where the schema for this XML instance is located
XmlSchemaCollectionName: Provides the name of the schema for this XML type.

Consider the typed XML is defined with the following TSQL:
-- Change to Library database
USE Library
-- OrderSchema is defined using the CREATE XML SCHEMA COLLECTION statement
CREATE XML SCHEMA COLLECTION OrderSchema AS
N'XSD_DEFINITION_HERE'--Consider the Schema/namespace
-- Customer table is created with a Typed XML column name OrderXml
CREATE TABLE Customer (CustomerId int, CustomerName varchar(40), OrderXml xml(OrderSchema))

The three-part name of the embedded XML schema can be got as follows:
sqlcommand1.CommandText = "SELECT OrderXml from Customer";
SqlDataReader sqldatareader1 = sqlcommand1.ExecuteReader();
DataTable datatable1 = sqldatareader1.GetSchemaTable(); // SchemaTable
Console.WriteLine(datatable1.Rows[0]["XmlSchemaCollectionDatabase"]); //returns Library
Console.WriteLine(datatable1.Rows[0]["XmlSchemaCollectionOwningSchema"]); //returns dbo
Console.WriteLine(datatable1.Rows[0]["XmlSchemaCollectionName"]); //retuns OrderSchema

Disclaimer: This posting is provided "AS IS" with no warranties, and confers no rights

XML Data type in ADO.Net v2.0 - Part II

sushilc — Tue, 03 Aug 2004 16:39:00 GMT

In this section we will look at ways ADO.Net v2.0 (Code named 'Whidbey') allows us to insert/delete/update Xml data values in a table containing Xml column in SQL Server 2005 (Code named 'Yukon'). With earlier versions of the .Net Framework (1.0 and 1.1) the System.Data.SqlClient namespace will consume and emit XML as String values.Because of this, it should not be a surprise that they would behave the same way with Whidbey. This was made so as to not break customers using this new datatype of the Server with older versions of the framework. Note: The examples below use the Customer table defined in the Part I of the blog.

Xml Values from DataReader: XML values in SqlDataReader are surfaced like any other type. The GetValue() method will get the Xml Value as String where as the GetSqlValue() method will get the value as an instance of SqlString. The following examples show both of the retrieval methods.

Get Value as XmlReader
    using (SqlCommand Cmd = Conn.CreateCommand())
    {
         Cmd.CommandText= "SELECT OrderXml FROM Customer WHERE CustomerId = 2";
         SqlDataReader Reader = Cmd.ExecuteReader();
         if (Reader.Read())
         {
                string XmlValue = (string) Reader.GetValue(0); //Gets the XML value as string
         }
    }

Get Value as SqlXml: With ADO.Net 2.0, we have introduced a new class SqlXml. This new class adds SQL-specific feature like null semantics to the XML type. This is consistent with other SqlTypes (like SqlString for VARCHAR, SqlInt16 for Integer). This class allows the user to create an XmlReader (not to be confused with DataReader) on the SqlXml value using the SqlXml.CreateReader method. An example is shown below:
    using (SqlCommand Cmd = Conn.CreateCommand())
    {
         Cmd.CommandText= "SELECT OrderXml FROM Customer WHERE CustomerId = 2";
        SqlDataReader Reader = Cmd.ExecuteReader();
        if (Reader.Read())
        {
            SqlXml SqlXmlValue = Reader.GetSqlXml(0);
              PrintXmlReader(SqlXmlValue.CreateReader()); //Gets the XmlReader from SqlXml object and prints it using a Helper function
        }
    }
Note:
1. In the above examples, SqlClient Managed Provider internally converts the Binary formatted XML that it receives from the server into string representation.
2. To get the XmlReader object for the XML data type, use the SqlXml.CreateReader method.

Parameterized Xml Values
XML values can also be used in parameters. The value itself can be expressed as a string, an XmlReader-derived type instance or a SqlXml object. Examples below show how to set the parameters for each of these values.

Xml Value as String In this example, the string is directly used to set the Parameter's Value
using (SqlConnection Conn = new SqlConnection (ConnectionString))
{
      Conn.Open();
      using (SqlCommand Cmd = Conn.CreateCommand())
      {
            //INSERT VALUES using PARAMS
            XmlReader XmlValue = new XmlTextReader("Sample.Xml");
            Cmd.CommandText = "INSERT INTO Customer VALUES (4,'Chris Andrews',@XmlFile)";
            Cmd.Parameters.AddWithValue("@XmlFile", "<order><item><id>20</id><name>Widgets</name><units>3</units></item></order>");
            Cmd.ExecuteNonQuery();
      }
}
Xml Value as SqlXml
Just like other types, SQL-specific type for XML can be used to set the Parameter's value for XML. SqlXml ctor() takes XmlReader or a Stream. The following example creates an instance of XmlTextReader and then sets the value of the parameter. An instance of XmlTextReader is created by opening a file with name:"Sample.Xml".
      using (SqlConnection Conn = new SqlConnection (ConnectionString))
      {
            Conn.Open();
            using (SqlCommand Cmd = Conn.CreateCommand())
            {
                //INSERT VALUES using PARAMS
                Cmd.CommandText = "INSERT INTO Customer VALUES (4,'Chris Andrews',@XmlFile)";
                SqlXml SqlXmlValue = new SqlXml( new XmlTextReader ("SampleInfo.Xml")); // This passes the file SampleInfo.Xml as the parameter's value
                Cmd.Parameters.AddWithValue("@XmlFile", SqlXmlValue);
                Cmd.ExecuteNonQuery();
          }
     }
Note: You have to make sure that the XmlReader that is passed as an argument is on the top most node, else partial results will be inserted in the table, depending on the current position of the XmlReader.

Disclaimer: This posting is provided "AS IS" with no warranties, and confers no rights

XML Data type in ADO.Net v2.0 - Part I

sushilc — Thu, 29 Jul 2004 20:24:00 GMT

After a long hiatus, let me start with how the new XML data type in SQL Server 2005 is exposed via ADO.Net 2.0. I will discuss this new data type in following parts:

XML data type in SQL Server 2005 – A brief Introduction : You can consider this as a crash course on XML data type in SQL Server 2005.
ADO.Net 2.0 and XML DataType
1. Getting XML values from SqlDataReader.
2. Passing XML values as Parameters

The following is section 1 of the 2 part series:

XML data type in SQL Server 2005 – A brief Introduction

A new scalar data type is introduced in SQL Server 2005 for storage and retrieval of XML data. XML value that is stored in the column is basically an XML fragment like single root, multiple roots, text nodes, empty string, text nodes at the top. Consider you want to create a Customer table with the following Columns:

CustomerId                   int,
CustomerName              varchar(40),
OrderXml                      xml

Here is an example showing how to create such a table and insert some values as literals using TSQL

Untyped XML
CREATE TABLE Customer (CustomerId int, CustomerName varchar(40), OrderXml xml)
go

INSERT INTO Customer VALUES (1,'Allison Gray',
     '<order>
        <item>
           <id>20</id>
           <name>Widgets</name>
           <units>3</units>
        </item>
     </order>')
go

Fact: If the string character is Unicode then the XML values is always parsed in as UTF-16.

Typed XML
The above XML data type is untyped meaning it is not associated with any schema. If we know that OrderXML adheres to one specific XML Schema, we can associate it to a previously loaded XML schema with the following syntax:
-- Consider the Schema/namespace - OrderSchema is defined using the CREATE XML SCHEMA COLLECTION statement
CREATE TABLE Customer (CustomerId int, CustomerName varchar(40), OrderXml xml(OrderSchema))
go

XML Methods
In addition to the above, XML data type has some methods. Some of them are:

Query method: Given a XQUERY as an argument, this method performs that query on the XML data type.

Value method: Given a XQUERY as an argument, this method runs the query and returns a scalar value.

Exist method: Given an XQUERY as an argument, this method returns 1 if the XQuery expression returns a non-empty result from the XML column else it returns 1.

Modify method: Used to modify XML data. Basically this performs XML data manipulation as specified in the arguments.

Since our goal is to see the interaction of XML data type with ADO.Net, the above introduction would suffice. There are other awesome features on XML data type on the server and are not discussed here due to the scope of the article.

Disclaimer: This posting is provided "AS IS" with no warranties, and confers no rights