How to Use Expressions to Perform Message Assignments

  • Article

You can use expressions to manipulate messages in various ways in your orchestration.

Referring to message fields

You can refer to a distinguished field in a message by appending the field name to the message name as follows:

MyMsg.Amount

In this example, MyMsg is the message, and Amount is a field that has been identified as a distinguished field for the message type that MyMsg is based on.

Assigning to messages and message parts

You can assign a message directly to another message, or a message part to a message part:

MyMsg=IncomingMsg;  
MyMsg.Invoice=IncomingMsg.Invoice;

In this example, Invoice is a message part based on a schema.

If you want to modify a property on a message that has already been constructed—such as a message that has been received—you must construct a new message by assigning the first to the second in a Construct Message shape, and modify the property on the new message within the same Construct Message shape.

Note

You cannot refer or assign to message fields, such as MyMsg.Invoice.MyField, unless they have been promoted; you can only refer or assign to entire messages, message parts, promoted message properties, or distinguished fields.

Adding message parts

You can add additional parts to an existing multipart message by using the XLANGs.BaseTypes.XLANGMessage.AddPart method. To do so, do the following:

  • Create a C# project and add a reference to Microsoft.XLANGs.BaseTypes.

  • Implement a public class similar to the following:

    public class MyAddPartHelper  
{  
     public static void AddPart(XLANGMessage msg, object part, String partName)  
     {  
          msg.AddPart(part, partName);  
     }  
}

    There are three overloaded methods for Microsoft.XLANGs.BaseTypes.AddPart:

    public void AddPart(object part, String partName);  
public void AddPart(XLANGPart part);  
public void AddPart(XLANGPart part, String partName);

  • In your BizTalk project, add a reference to the public class and call the AddPart method from the Expression shape in your orchestration as follows:

    MyAddPartHelper.AddPart(myMessage, myStringObject, “StringObject1”);

Note

You cannot add non-serializable objects or custom formatted objects as message parts. All static parts must be initialized before adding additional parts using the AddPart method. You can add arbitrary parts to a message only inside its message construct statement. Adding additional parts outside of the message construct statement is not supported.

Retrieving message parts

You can retrieve a message part from an existing multipart message by using the RetrieveAs method from Microsoft.XLANGs.BaseTypes. To do so, do the following:

  • Create a C# project and add a reference to Microsoft.XLANGs.BaseTypes.

  • Implement a public class similar to the following:

    Public class MyAddPartHelper  
{  
     public static Object GetPart(XLANGMessage msg, string sName, Type t)  
     {  
          XLANGPart p =  msg[sName];  
          return p.RetrieveAs(t);  
     }  
     public static Object GetPart(XLANGMessage msg, int partIndex, Type t)  
     {  
           XLANGPart p = msg[partIndex];  
           return p.RetrieveAs(t);  
      }  
}

    Note

    The RetrieveAs method supports retrieving message parts by name and by index.

  • In your BizTalk project, add a reference to the public class and call the GetPart method from the Expression shape in your orchestration as follows:

    sPart = (System.String) MyAddPartHelper.GetPart(msg, "StringObject1" , typeof(System.String));  
//sPart is a type of System.String  
sPart = (System.String) MyAddPartHelper.GetPart(msg, 1, typeof(System.String));  
//Retriving the message part with index = 1

Message part context property access

A message part has context separate from the message context. You can construct message part context properties through the schema editor when you set the Property Schema Base property for the associated element to PartContextPropertyBase.

The access is similar to message properties, through an expression like:

Msg.PartName(myPartContextProperty)

For example:

Str=Msg.PartName(myPartContextProperty); //assumes myPartContextProperty is of type string

XLANGMessage context property access

If you would like to access message properties from the XLANGMessage interface from your code, you can pass the message as a parameter of type Microsoft.XLANGs.BaseTypes.XLANGMessage to a method from an Expression shape, and then use the Microsoft.XLANGs.BaseTypes.XLANGMessage methods SetPropertyValue and GetPropertyValue to achieve this. To do so, do the following:

  • Create a C# project and add a reference to Microsoft.XLANGs.BaseTypes and Microsoft.BizTalk.GlobalPropertySchemas.

  • Access the context property using the code similar to the below:

    MyMsg.GetPropertyValue(typeof(BTS.MessageID));  
MyMsg.SetPropertyValue(typeof(MIME.IsMultipartRelated), true);

Note

If you would like to get or set your own custom context properties, you need to add a reference to your property schema project or add a reference to the assembly contains the property schemas in your C# project.

Assigning to message properties

You can assign a value to a message property:

MyMessage(MySchemaNamespace.MyProperty)=True;

In BizTalk Server you can refer to and assign values to the MIME properties of a multi-part message:

Message_Out.MessagePart_1(MIME.FileName)="document.doc";

Note

A BizTalk message consists of message context and message parts. You must first initialize the message parts before you can get or set any message context property; otherwise, you will receive error during the XLANG compile time.

See Also

Using Messages in Orchestrations
Constructing Messages in User Code