tailieunhanh - Pro BizTalk 2006 phần 3

Trong trường hợp của hệ thống ERP, nếu điều này là một ứng dụng SAP, cổng sẽ sử dụng các bộ chuyển đổi SAP. Điều này cũng sẽ đúng nếu nó là một hàng đợi MQSeries-cổng sẽ sử dụng một bộ chuyển đổi MQSeries. Đối với các giải pháp vận chuyển tùy chỉnh, | CHAPTER 3 THINKING INSIDE THE BOX 79 Performance Large message properties cannot be streamed and must be entirely loaded into memory by the runtime. This will become an issue if you write large values for message properties into the message context. Overwriting of promoted properties If you have promoted a property to the message context and you issue a context write operation the property is no longer promoted. Dealing with Nulls Null properties are not persisted to the context. If you set a property s value to Null it will no longer exist and you cannot see a context property in the HAT with a value of Null. Distinguished Fields There are two types of property promotion distinguished fields and property fields. The latter type uses property schemas. In the BizTalk schema editor you manage both of these types of property promotion by using the Promote Properties dialog box which you access by using the Promote Properties property of the Schema node. Distinguished fields are only useful when they are accessed within orchestration. Promoted properties can be accessed either in orchestrations or from custom code routing and pipelines. Distinguished fields on the other hand cannot be used for routing and are only used by the orchestration engine. When dealing with large messages this can save significant server processing as the engine would need to use XPath expressions to search through the document to find the piece of data that it needs each time the expression is evaluated. This way the data is loaded once when the document is parsed by the runtime engine. Distinguished fields are used within orchestrations to move required elements into the context and only read the context property within the orchestration without having to load the entire document into memory. Distinguished fields also offer nice IntelliSense capabilities within the orchestration expression editor and message assignment shapes. Depending on the type of access that is needed you can choose to .