WSO2 BPS - Extensions - Flexible Assigns

Flexible Assigns


Auto Complete Copy Destination (L-Value)

A lot of times, users expect the <copy> operation in a WS-BPEL assign activity to behave such that the path specified by the destination ("to-spec") is automatically created, if it doesn't already exist. By default, if the to-spec used within a <copy> operation does not select exactly one XML information item during execution, then the standard fault bpel:selectionFailure is thrown (as mandated by the spec).

To override this default behavior, we introduce a insertMissingToData attribute in the <copy> operation, which if it is set to "yes", will instruct the runtime to complete the (XPath) L-value specified by the to-spec, if no items were selected. For the sake of simplicity, we will complete the to-spec if and only if:

  1. It's a path expression whose steps are separated by "/", and
  2. Its steps have an axis, which is either "child" or "attribute", and
  3. Its steps have no following predicates, and
  4. Its steps test the name of a node, without the use of wild cards.

Formally, the grammar of the to-spec, for which auto-complete is enabled, may be defined in terms of these productions:

            PathExpr ::= ("/" RelativePathExpr?) | RelativePathExpr
            RelativePathExpr ::= ForwardStep (("/" ) ForwardStep)*
            ForwardStep ::= (ForwardAxis QName) | AbbrevForwardStep
            AbbrevForwardStep ::= "@"? QName
            ForwardAxis ::= ("child" "::") | ("attribute" "::")
        

The example below illustrates the use of the insertMissingToData attribute. Let's say that the variable "response" is uninitialized. In that case, the first <copy> operation will fail, whereas the second one will succeed.


Add support for the ignoreMissingFromData attribute in <copy>

The attached patch adds support for the following attributes in the BPEL assign activity's copy operation:

  1. The optional @ignoreMissingFromData attribute, which if it has the value of "yes", and the from-spec returns zero XML information items, then no bpel:selectionFailure is thrown, and the to-spec is not evaluated.
  2. An extension @ignoreUninitializedFromVariable attribute, which if it has the value of "yes", and the from-spec contains an uninitialized variable, then no bpel:uninitializedVariable is thrown, and the to-spec is not evaluated.

The informal syntax of the above attributes is shown below:

            <copy ignoreMissingFromData="yes|no"? ignoreUninitializedFromVariable="yes|no"?>
                  from-spec to-spec
            </copy>