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:
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.
The attached patch adds support for the following attributes in the BPEL assign activity's copy operation:
The informal syntax of the above attributes is shown below:
<copy ignoreMissingFromData="yes|no"? ignoreUninitializedFromVariable="yes|no"?> from-spec to-spec </copy>