[Fdo-trac] [fdo-trac] #740: Properties with NULL Values are not Included in XML Output

[FDO]

#740: Properties with NULL Values are not Included in XML Output
-----------------------------------------+-----------------------------
 Reporter:  crispinatime                 |        Owner:  brentrobinson
     Type:  defect                       |       Status:  closed
 Priority:  minor                        |    Milestone:  3.6.0
Component:  FDO API                      |      Version:  3.6.0
 Severity:  3                            |   Resolution:  fixed
 Keywords:  xmlFeatureSerialize XML GML  |  External ID:
-----------------------------------------+-----------------------------
Changes (by jng):

 * resolution:   => fixed
 * status:  new => closed

Comment:

 In [changeset:"8409" 8409]:
 {{{#!CommitTicketReference repository="" revision="8409"
 Serialize null property values as xsi:nil elements

 Fixes #740.

 #740 Properties with NULL Values are not Included in XML Output.
 FdoXmlFeatureSerializer::XmlSerialize() discarded every property whose
 value the
 feature reader reported as null, so the features written by one call had
 different shapes: a record with a null property was missing that property
 element altogether, and the gml:featureMembers of an export carried
 different
 properties from record to record.

 A property that the reader reports without a value is now written as a
 property
 element with an xsi:nil="true" attribute, which is how XML Schema and GML
 represent a null value, so every feature written by a call carries the
 same
 property elements. Nothing is written, as before, for a property the
 reader does
 not report at all - one left out of the select, or one of the GML
 name/description/id relate properties, whose names ("gml/name") are not
 element
 names - and object and association properties still go through their own
 sub-writers, which write a feature collection and write nothing when it
 has no
 members.

 The managed wrapper forwards its arguments straight to these classes, so
 no
 managed code change is needed.

 * FeatureSerializer.cpp: _writeProperty() writes a null property that the
 reader
   reports (GetPropertyIndex() finds it among the properties of the feature
 being
   read) and that has a value of its own to be missing (a data or a
 geometric
   property) as a property value with no value, which is FDO's null value
 for a
   property.
 * FeaturePropertyWriter.cpp: WriteProperty() writes an FdoPropertyValue
 that has
   no value as <prop xsi:nil="true"/>, and declares the xsi prefix on the
   property element itself when the caller has not already declared it in
 scope.
   A value-only write writes nothing, since a null property's only content
 is the
   attribute.
 * FeaturePropertyReaderImpl.cpp: an element carrying xsi:nil="true", or
 the
   other XML Schema literal "1", is a property with no value: its content
 is not
   parsed and the property is reported to the feature handler with no
 value, so
   that the feature reports it as null instead of as an empty value or an
 empty
   geometry.
 * FeatureReaderImpl.cpp: AddDataProperty() registers the name of a
 property that
   is reported with no value, so that IsNull() reports it as null while it
 stays
   part of the feature. GetPropertyIndex() and GetPropertyName() reported
 the
   property list of the reader itself, which for a reader over a feature
   collection is empty; they now report that of the feature being read, as
   IsNull() and GetString() already did.
 * FeatureSerializer.h, FeaturePropertyWriter.h: document what a null
 property
   value is written as.

 Tests: GmlWriteTest::testNullProperty serializes a reader whose int32Prop,
 stringProp and geoProp have no value, requires each of its two features to
 carry
 all three as xsi:nil elements, and then reads the document back and
 requires
 them to come back as null properties of the feature, with the properties
 that do
 have values untouched. GmlWriteTest::testWriteNullProperty drives the
 property
 writer directly, with a property value that has no value and one that has,
 and
 requires the first to be the xsi:nil element with the XMLSchema-instance
 namespace declared on it, since the caller declared none.
 GmlTest::testNullProperty
 reads a document containing xsi:nil="true", xsi:nil="1", xsi:nil="false"
 and an
 empty element, and requires the first two to be null and the last two to
 keep
 their (empty) values. All three failed before the fix: no xsi:nil element
 was
 written for a null property, the property writer dereferenced a null
 value, and
 an xsi:nil element in a document was read as an empty value rather than as
 a
 null.

 Validation: FDOCore UnitTest on ubuntu22 amd64, Debug OK (129) and Release
 OK
 (129), against OK (126) for the same tree before the change; the three new
 tests
 are the difference. The Debug run reports 0 direct and 50 indirect
 LeakSanitizer
 records, 220980 bytes in 2418 allocations, the same totals the suite
 reported
 before the change. UnitTestMySql OK (249), which includes
 MySqlFdoImportExportTest OK (4), the suite that round-trips features
 through the
 XML serializer and the XML reader, and its LeakSanitizer report is also
 unchanged (0 direct, 318 indirect, 46236 bytes in 491 allocations).

 API/ABI: the cycle is in freeze mode, and no provider-facing surface
 moves. The
 only shipped headers touched are FeatureSerializer.h and
 FeaturePropertyWriter.h, in comments; the new code is file-local. nm -D
 over
 libFDO against the fdosdk 8364 baseline reports no removed symbols, and
 the five
 symbols it reports as added are the ones the previous change added.
 }}}
-- 
Ticket URL: <https://trac.osgeo.org/fdo/ticket/740#comment:2>
FDO <http://fdo.osgeo.org/>
Feature Data Objects