Ichthyostega
aa335b5605
Added warning tags to several headers of the first config system draft from 2008 since this effort is stalled and likely to be implemented differently
130 lines
3.9 KiB
C++
130 lines
3.9 KiB
C++
/*
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QueryResolver - interface for discovering contents of a scope
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Copyright (C) Lumiera.org
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2009, Hermann Vosseler <Ichthyostega@web.de>
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of
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the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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* *****************************************************/
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/** @file query-resolver.cpp
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** implementation of a framework to query and discover elements
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** based on logical rules. This framework builds on the notion of
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** possibly having several QueryResolver facilities to handle various
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** kinds of queries in an uniform way. To reflect that design, the
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** implementation is built round a DispatcherTable to forward requests
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** to concrete entities implementing the QueryResolver interface. The
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** actual query resolution mechanism is thus not part of the framework.
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**
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*/
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#include "lib/multifact.hpp"
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#include "common/query/query-resolver.hpp"
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namespace lumiera {
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/* generate vtables here... */
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Goal::~Goal() { }
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Resolution::~Resolution() { }
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QueryResolver::~QueryResolver() { }
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typedef Goal::QueryID const& QID;
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/* == dispatch to resolve typed queries == */
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using lib::factory::BuildRefcountPtr;
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using lib::factory::MultiFact;
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/** factory used as dispatcher table
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* for resolving typed queries */
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typedef MultiFact< Resolution*(Goal const&) // raw signature of fabrication
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, Goal::QueryID // select resolution function by kind-of-Query
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, BuildRefcountPtr // wrapper: manage result set by smart-ptr
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> DispatcherTable; //
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/** PImpl of the generic QueryResolver */
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class QueryDispatcher
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: public DispatcherTable
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{
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public:
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PReso
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handle (Goal const& query)
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{
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QID qID = query.getQID();
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ENSURE (contains (qID));
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return this->invokeFactory (qID, query);
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} // qID picks the resolution function
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};
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QueryResolver::QueryResolver ()
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: dispatcher_(new QueryDispatcher)
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{ }
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/** @par implementation
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* For actually building a result set, the QueryResolver base implementation
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* uses an embedded dispatcher table. The concrete query resolving facilities,
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* when implementing the QueryResolver interface, are expected to register
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* individual resolution functions into this QueryDispatcher table.
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* Whenever issuing a Goal, a suitable resolution function is picked
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* based on the Goal::QueryID, which contains an embedded type code.
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* Thus, the individual resolution function can (re)establish a
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* typed context and downcast the Goal appropriately
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*/
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PReso
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QueryResolver::issue (Goal const& query) const
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{
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REQUIRE (!dispatcher_->empty(), "attempt to issue a query without having installed any resolver (yet)");
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if (!canHandle (query))
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throw lumiera::error::Invalid ("unable to resolve this kind of query"); //////////////////////////////////TICKET #197
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return dispatcher_->handle(query);
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}
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void
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QueryResolver::installResolutionCase (QID qID, ResolutionMechanism resolutionFun)
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{
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ENSURE (!dispatcher_->contains (qID),
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"duplicate registration of query resolution function");
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dispatcher_->defineProduction (qID, resolutionFun);
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}
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} // namespace lumiera
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