An elementary query or statement is a (single select) statement whose parts are
not covered by the various set and get methods of the composer. That is, if the
elementary statement contains a filter clause, a call to
XSingleSelectQueryAnalyzer::getFilter will not return you this
filter. Instead, only filters which have been set using for instance setFilter
are covered by the get methods.
The only methods which take all parts of the elementary statement into account are
XSingleSelectQueryAnalyzer::getQuery and
XSingleSelectQueryAnalyzer::getQueryWithSubstitution, which always returns
the complete composed query.
As a result, you can use the composer to build culmulative filter expressions. That
is, you can set ElementaryQuery to a statement already containing
filters, and then use setFilter to append additional filters.
The very same holds for sort orders, HAVING and GROUP BY
clauses.
There are various use cases for this. For instance, you might want to use the
statement represented by a QueryDefinition, and extend it with additional
filters or sort orders, while not touching the respective parts already present
in QueryDefinition::Command. This can be achieved by setting the
QueryDefinition::Command as ElementaryQuery of a
SingleSelectQueryComposer.
If, in such a scenario, you would be interested in the filter part of the
QueryDefinition::Command, you would set it via
XSingleSelectQueryAnalyzer::setQuery, and retrieve the filter
part via XSingleSelectQueryAnalyzer::getFilter.
If you'd be interested in the composed filter, you would set the
QueryDefinition::Command as ElementaryQuery, add your
filter, and propagate the resulting query (XSingleSelectQueryAnalyzer::getQuery)
to an SingleSelectQueryAnalyzer instance via
XSingleSelectQueryAnalyzer::setQuery.
