IBM Integration Bus, Version 9.0.0.8 Operating Systems: AIX, HP-Itanium, Linux, Solaris, Windows, z/OS

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Handling nulls in message maps

A message might contain fields that can carry a specific out-of-range value. This is distinct from the field being empty. Such values are termed nil or null, and the field is said to be nillable or nullable.

The logical message tree supports the concept of out-of-range values by using one of two techniques, depending on the data format:

For XML the schema model allows for elements to be defined as nillable to indicate that they support an out-of-range value. An XML element in a document is identified as being nilled by having a xsi:nil attribute with the value 'true'. The XMLNSC parser logical tree for a nilled element has an empty value and a child xsi:nil attribute with the value 'true'.
For other text and binary messages modeled with a DFDL schema or MRM message set, elements can also be defined as nillable to indicate that they support an out-of-range value. In the message bit stream, a reserved value is identified to indicate the nulled state. The DFDL and MRM parsers logical tree for a nilled element have the value set to the special value NULL.

When you map nilled values, consider the following behavior when using the Move transform, Custom Java, or Custom ESQL to set a target.

Source	Target	Comment
Logical Message Tree XML nillable element	XML nillable	Target created as nilled, has xsi:nil attribute 'true', if source has xsi:nil attribute 'true'.
Logical Message Tree XML nillable element	Non-XML nillable	Target created with NULL value, if source has xsi:nil attribute 'true'.
Logical Message Tree XML element set to NULL	XML or non-XML nillable	Target created with empty value. A Source XML having NULL value is not considered a nilled element.
Logical Message Tree non-XML	XML nillable	Target created as nilled, has xsi:nil attribute 'true', if source is NULL.
Logical Message Tree non-XML	Non-XML nillable	Target created with NULL value, if source is NULL.
Database nullable column	XML nillable	Target created as nilled, has xsi:nil attribute 'true', if source is SQL NULL.
Database nullable column	Non-XML nillable	Target created with NULL value, if source is SQL NULL.
Custom ESQL	XML nillable	Target created as nilled, has xsi:nil attribute 'true', if return is ESQL NULL
Custom ESQL	Non-XML nillable	Target created as nilled, if return is ESQL NULL
Custom Java	XML nillable	Target created as nilled, has xsi:nil attribute 'true', if return is an MbElement with type set to “TYPE_UNKNOWN” and a value of “null” and a child element xsi:nil 'true'.
Custom Java	Non-XML nillable	Target created as nilled, if return is an MbElement with type set to "TYPE_UNKNOWN" and a value of "null"

Definitions:

In the preceding table, XML means XMLNSC or XMLNS logical trees. The term non-XML means MRM or DFDL logical trees, and applies to all MRM physical formats, including MRM XML.

Use XPath functions to determine the state of a source element.

XPath function	Usage	Source element	Output
fn:empty	Tests whether a set of elements is empty	A single XML or non-XML element that is present and nilled	false
fn:empty	Tests whether a set of elements is empty	A NULL value in a logical tree	false
fn:empty	Tests whether a set of elements is empty	A missing element, not present in the logical tree	true
fn:nilled	Tests whether an element is nilled	A nillable XML element	true only if the xsi:nil attribute is present and set to 'true' in the logical tree
fn:nilled	Tests whether an element is nilled	A nillable non-XML element	true only if the value in the logical tree is NULL
fn:exists	Tests whether an element exists	A single XML or non-XML element	true if the element is present in the logical tree, regardless of the nillable and nilled state
fn:exists	Tests whether an element exists	A NULL value in a logical tree	true
fn:exists	Tests whether an element exists	A missing element, not present in the logical tree	false

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Last updated Friday, 21 July 2017