fskorgen commented on issue #6972:
URL: https://github.com/apache/hop/issues/6972#issuecomment-4212769942
@hansva One more question:
When using the legacy getXml() functions, we often skip XML elements when
the value is empty or equal to the default value. This is done to reduce the
size of the generated XML.
We have some projects where we read datalake files and load data into
database tables. In these projects, we map many hundreds of tables with a large
number of fields (up to 500). Omitting empty or default values helps keep the
XML manageable, but it also means the deserialization logic must correctly
handle missing elements and apply the expected defaults.
Is there a way to define default values in the annotation and have values
equal to those defaults be skipped during serialization?
For example, for one field read from the datalake, the legacy getXml() code
looks like this:
for (CloudApiField field : argumentFields) {
xml.append(" <field>").append(Const.CR);
xml.append(" ").append(XmlHandler.addTagValue("name",
field.getName()));
xml.append(" ").append(XmlHandler.addTagValue("attribute",
field.getAttribute()));
xml.append(" ").append(XmlHandler.addTagValue("type",
field.getTypeDesc()));
if (Strings.isNotBlank(field.getFormat())) {
xml.append(" ").append(XmlHandler.addTagValue("format",
field.getFormat()));
}
xml.append(" ").append(XmlHandler.addTagValue("length",
field.getLength()));
if (field.getPrecision() != -1) {
xml.append(" ").append(XmlHandler.addTagValue("precision",
field.getPrecision()));
}
if (Strings.isNotBlank(field.getDecimalSymbol())) {
xml.append(" ").append(XmlHandler.addTagValue("decimal",
field.getDecimalSymbol()));
}
if (Strings.isNotBlank(field.getTrimTypeCode()) ||
"none".equals(field.getTrimTypeCode())) {
xml.append(" ").append(XmlHandler.addTagValue("trim_type",
field.getTrimTypeCode()));
}
if (Strings.isNotBlank(field.getComments())) {
xml.append(" ").append(XmlHandler.addTagValue("comments",
field.getComments()));
}
xml.append(" </field>").append(Const.CR);
}
With annotations, the XML becomes (e.g two fields):
<field>
<name>MBCONO</name>
<attribute>[CONO]</attribute>
<type>Integer</type>
<length>3</length>
<format>0</format>
<trim_type>none</trim_type>
<precision>-1</precision>
<decimal/>
<group/>
<comments>company (x)</comments>
</field>
<field>
<name>MBWHLO</name>
<attribute>[WHLO]</attribute>
<type>String</type>
<length>3</length>
<format/>
<trim_type>none</trim_type>
<precision>-1</precision>
<decimal/>
<group/>
<comments>warehouse (x)</comments>
</field>
With the legacy method, the XML is:
<field>
<name>MBCONO</name>
<attribute>[CONO]</attribute>
<type>Integer</type>
<format>0</format>
<length>3</length>
<comments>company (x)</comments>
</field>
<field>
<name>MBWHLO</name>
<attribute>[WHLO]</attribute>
<type>String</type>
<length>3</length>
<comments>warehouse (x)</comments>
</field>
So the annotation-based approach produces significantly more XML for large
mappings. It would be useful if annotations could support default values and
omit fields that are empty or equal to those defaults, similar to the legacy
behavior.
If you want, I can also make this more concise and more natural for a GitHub
issue comment.
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