Biztalk : Using XPaths in Message Assignment

You can use the xpath function to assign an XPath value to a message part, or to assign a value to an XPath that refers to a message part. For more information on assigning to messages and message parts, see Constructing Messages.

Note  The use of the xpath function is not limited to message assignment. You can also use it in any expression, for example:

If ((System.Double) xpath(_RequestMessage.part, "number(//book[last()]/price)") == 75.00 && (System.Boolean) xpath(msgBoolean, "string(//boolean)") == false)...

Note  If you want to assign a value to a string, use the XPath string() function. For example:

myString = xpath(msg, "string(/*/book[1]/title)");

Note  The engine is not schema-aware, so you can only read values from or write values to a node that exists in the containing message (the complete path must exist), or the engine will raise an exception. This is true even if you supply a default value.

Assigning to an XPath in a message part

Consider the following schema:

<?xml version="1.0" encoding="utf-16"?>
<xs:schema xmlns:b="http://schemas.microsoft.com/BizTalk/2003" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="catalog">
    <xs:complexType>
      <xs:sequence>
        <xs:element minOccurs="1" maxOccurs="unbounded" name="book">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="title" type="xs:string" />
              <xs:element name="author">
                <xs:complexType>
                  <xs:sequence>
                    <xs:element name="FirstName" type="xs:string" />
                    <xs:element name="LastName" type="xs:string" />
                  </xs:sequence>
                </xs:complexType>
              </xs:element>
              <xs:element name="price" type="xs:string" />
            </xs:sequence>
            <xs:attribute name="country" type="xs:string" />
          </xs:complexType>
        </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>
You can use the XPath function as follows to set values on a document instance of that schema type:
construct _ResponseMessage
{
_ResponseMessage.part = _RequestMessage.part;
xpath(_ResponseMessage.part, "/*/book[1]/@country") = "USA";
xpath(_ResponseMessage.part, "/*/book[1]/title") = "Legends";
xpath(_ResponseMessage.part, "/*/book[1]/author/FirstName") = "A";
xpath(_ResponseMessage.part, "/*/book[1]/author/LastName") = "B";
xpath(_ResponseMessage.part, "/*/book[1]/price") = 50;
}

Assigning to a message part from an XPath

construct objMessage
{
objMessage.BooleanPart = xpath("false()");
objMessage.IntPart = xpath("100");
objMessage.StringPart = xpath("'Hello'");
objMessage.StringPart2 = xpath("'World'");
}

Using XPath to assign from nodes and node sets

You can also use XPath to assign XML nodes and node sets to an XML element, a class, or a schema-based or class-based message.
Suppose you have an XML-serializable class called Book, and consider the following examples:

[Serializable]
Class Book {...}

Example One — select the fourth book element from the catalog, and assign it to an XML element variable:

myXmlElement = xpath(myMsg, "/catalog/book[3]");

Example Two — select the fourth book element from the catalog, and convert it using XML deserialization into a Book class instance:

myBook = xpath(myMsg, "/catalog/book[3]");

Example Three — select the fourth book element from the catalog, and convert it a message of type Book:

myBookMsg = xpath(myMsg, "/catalog/book[3]");

Example Four — select all book elements in the catalog, where MyMethod takes an XmlNodeSet as a parameter:

MyMethod(xpath(myMsg, "/catalog/book"));

Example Five — add a book element to the "BookOfTheMonth" container:

xpath(MyMsg2, "/RecommendedBooks/BookOfTheMonth") = myBook;

Example Six — add all books that are priced at twenty or less to a set of recommended books:

xpath(MyMsg2, "/RecommendedBooks/BestPriceBooks") = xpath(MyMsg, "/catalog/book[@price <= 20]");

Example Seven — call user code that returns an XML element:

xpath(MyMsg2, "/RecommendedBooks/AdvertisedByPartner") = GetPartnerAdvertisedBook();

Before applying examples five and seven:

<RecommendedBooks>
       <BookOfTheMonth/>
       <BestPriceBooks/>
       <AdvertisedByPartner/>
</RecommendedBooks>

After applying examples five and seven:

<RecommendedBooks>
       <BookOfTheMonth>
              <Book country="USA">
                     <title>McSharry</title>
                     <author>
                            <FirstName>Nancy</FirstName>
                            <LastName>Jensen</LastName>
                     </author>
              </Book>
       </BookOfTheMonth>
       <BestPriceBooks/>
       <AdvertisedByPartner>
              <Book country="USA">
                     <title>The Rooster</title>
                     <author>
                            <FirstName>Mindy</FirstName>
                            <LastName>Martin</LastName>
                     </author>
              </Book>
       </AdvertisedByPartner>
</RecommendedBooks>

Source : MSDN