Accessing attributes in a message in the MRM domain

When an MRM message is parsed into a logical tree, attributes and the data that they contain are created as name-value pairs in the same way that MRM elements are. The ESQL that you code to interrogate and update the data held in attributes refers to the attributes in a similar manner.

Consider the sample MRM message. The attribute LastName is defined as a child of the Name element in the Customer message. 

Here is an example input XML message:

 

<Customer xmlns:addr="http://www.ibm.com/AddressDetails" 

xmlns:brw="http://www.ibm.com/BorrowedDetails">
   <Name LastName="Bloggs">
      <Title>Mr</Title>
      <FirstName>Fred</FirstName>
   </Name>
   <addr:Address>
      <HouseNo>13</HouseNo>
      <Street>Oak Street</Street>
      <Town>Southampton</Town>
   </addr:Address>
             <ID>P</ID>
   <PassportNo>J123456TT</PassportNo>
   <brw:Borrowed>
      <VideoTitle>Fast Cars</VideoTitle>
      <DueDate>2003-05-23T01:00:00</DueDate>
      <Cost>3.50</Cost>
   </brw:Borrowed>
   <brw:Borrowed>
      <VideoTitle>Cut To The Chase</VideoTitle>
      <DueDate>2003-05-23T01:00:00</DueDate>
      <Cost>3.00</Cost>
   </brw:Borrowed>
   <Magazine>0</Magazine>
</Customer>

When the input message is parsed, values are stored in the logical tree as shown in the following section of user trace:

(0x0100001B):MRM = (
  (0x01000013):Name = (
    (0x0300000B):LastName = 'Bloggs'
    (0x0300000B):Title = 'Mr'
    (0x0300000B):FirstName = 'Fred'
  )
  (0x01000013)http://www.ibm.com/AddressDetails:Address = (
    (0x0300000B):HouseNo = 13
    (0x0300000B):Street = 'Oak Street'
    (0x0300000B):Town = 'Southampton'
  )
  (0x0300000B):ID = 'P'
  (0x0300000B):PassportNo = 'J123456TT'
  (0x01000013)http://www.ibm.com/BorrowedDetails:Borrowed = (
    (0x0300000B):VideoTitle = 'Fast Cars'
    (0x0300000B):DueDate = TIMESTAMP '2003-05-23 00:00:00'
    (0x0300000B):Cost = 3.50
  )
  (0x01000013)http://www.ibm.com/BorrowedDetails:Borrowed = (
    (0x0300000B):VideoTitle = 'Cut To The Chase '
    (0x0300000B):DueDate = TIMESTAMP '2003-05-23 00:00:00'
    (0x0300000B):Cost = 3.00
  )
  (0x0300000B):Magazine = FALSE

The following ESQL changes the value of the LastName attribute in the output message:

SET OutputRoot.MRM.Name.LastName = 'Smith';

Be aware of the ordering of attributes when you code ESQL. When attributes are parsed, the logical tree inserts the corresponding name-value before the MRM element's child elements. In the previous example, the child elements Title and FirstName appear in the logical message tree after the attribute LastName. In the Broker Application Development perspective, the Outline view displays attributes after the elements. When you code ESQL to construct output messages, you must define name-value pairs for attributes before any child elements.