ERROR: GIN indexes do not support whole-index scans

<div class="Section1"><p class="MsoNormal">Could anyone advise as to how to avoid this error? I’ll describe the table
andquery below.<p class="MsoNormal"> <p class="MsoNormal">The database contains a table ‘tinytm_segments’, which has
twotext columns, ‘source_text’ and ‘target_text’. These are used to store sentences and their translations. The
languageof the text is specified with typical two-character identifiers (‘en’, ‘fr’ etc.) stored in two further
columns,‘source_lang_code’ and ‘target_lang_code’. Translation in either direction can be stored, so for a given row,
source_textmay contain English and target_text French (with the corresponding values in source_lang_code and
target_lang_code),or the other way round.<p class="MsoNormal"> <p class="MsoNormal">The application needs to search for
(say)French sentences containing a given substring and retrieve any English translation found (or whatever other
languagecombination and direction). To perform better with large datasets, full text indices are defined, such as
these:<pclass="MsoNormal"> <p class="MsoNormal">-- Index English text<p class="MsoNormal">CREATE INDEX
tu_target_text_en_idxON tinytm_segments USING gin(to_tsvector('english', target_text)) where target_lang_code = 'en';<p
class="MsoNormal">CREATEINDEX tu_source_text_en_idx ON tinytm_segments USING gin(to_tsvector('english', source_text))
wheresource_lang_code = 'en';<p class="MsoNormal"> <p class="MsoNormal">-- Index French text<p class="MsoNormal">CREATE
INDEXtu_source_text_fr_idx ON tinytm_segments USING gin(to_tsvector('french', source_text)) where source_lang_code =
'fr';<pclass="MsoNormal">CREATE INDEX tu_target_text_fr_idx ON tinytm_segments USING gin(to_tsvector('french',
target_text))where target_lang_code = 'fr';<p class="MsoNormal"> <p class="MsoNormal">To retrieve (say) sentences that
havebeen translated from French, where the French contains a given substring, a query like this can then be issued:<p
class="MsoNormal"> <pclass="MsoNormal">SELECT * FROM  tinytm_segments WHERE<p class="MsoNormal"
style="text-indent:36.0pt">source_lang_code='fr' AND <p class="MsoNormal"
style="text-indent:36.0pt">to_tsvector('french',source_text) @@ plainto_tsquery('french', 'rien du tout') AND
lower(source_text)LIKE '%rien du tout%'<p class="MsoNormal" style="text-indent:36.0pt"> <p class="MsoNormal">However,
thatwill return sentences translated into whatever language. The error occurs when trying to retrieve only sentences
translatedfrom French into English, using a query like this:<p class="MsoNormal"> <p class="MsoNormal">SELECT * FROM 
tinytm_segmentsWHERE<p class="MsoNormal" style="text-indent:36.0pt">source_lang_code='fr'  AND <p class="MsoNormal"
style="text-indent:36.0pt">to_tsvector('french',source_text) @@ plainto_tsquery('french', 'rien du tout') AND
lower(source_text)LIKE '%rien du tout%'<p class="MsoNormal" style="text-indent:36.0pt"> AND target_lang_code='en'<p
class="MsoNormal"> <pclass="MsoNormal">Why would adding “target_lang_code=’en’” cause this error?<p
class="MsoNormal"> <pclass="MsoNormal">Environment: PostgreSQL 8.4 on Windows (installed with one-click installer),
defaulttext search config used.<p class="MsoNormal"> <p class="MsoNormal">Thanks in advance for any information.<p
class="MsoNormal"> <pclass="MsoNormal">Kevin.<p class="MsoNormal"> </div>