Declare an updating function.

Related Syntax Constructs

The following construct(s) refer to this construct:

• Prolog

---

Syntax

Description

An UpdatingFunctionDecl declares an updating function. The declaration differs from the declaration of a non-updating function by the additional "updating" keyword, the absence of a result type specification, and an UpdateSequence instead of a result expression.

The UpdatingFunctionDecl occurs in the prolog of an update statement or a library module declaration. Although it is also syntactically valid in the prolog of a query, it is useless in queries because it can only be invoked from updating expressions.

Example

• This function inserts an attribute with the specified name into an element if it does not exist, or modifies the attribute value if it does exist.

  declare updating function local:upsert($e as element(), 
                                                               $an as xs:QName, 
                                                               $av as xs:string) 
  { 
  	let $ea := $e/attribute()[node-name(.) = $an] 
  	do if ($ea) then 
  		replace $ea with attribute {$an} {$av}
  	     else 
  		insert attribute {$an} {$av} into $e 
  }