query.hpp File Reference

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Description

Basic and generic representation of an internal query.

This header provides the foundation for issuing queries instead of using hard wired logic and defaults. This is a fundamental architecture pattern within Lumiera, and serves to decouple the parts of the application and allows for a rules based configuration and orchestration of the internal workings.

A Query is a request for just someone to come up with a solution, a preconfigured setup, some existing data object or contextual information. In order to be usable, actually a QueryResolver needs to be available to compute the solution and retrieve the results. As a common denominator, queries can be generic queries given in predicate logic syntax; in this case a generic query resolver (Planned feature as of 1/2013) will be able at least to determine a suitable facility for delegating the resolution. Besides, specific subsystems are using more specific kinds of queries and provide a specialised resolution mechanism, kind of a shortcut, which in these cases can be addressed directly.

General usage pattern

Some parts of the application allow to issue queries – typically these parts do also expose a service point for clients to issue similar queries. In any case, a query remains in the ownership of the issuer, which is also responsible to keep the storage alive during results retrieval. Queries can't be copied and are passed by reference, since #Query is an interface baseclass. Each query instance bears at least a type tag to indicate the type of the returned result, plus a classification tag to indicate the kind of query. In addition, queries are usually required to provide a syntactical representation, allowing to transform each query into a generic query.

To resolve the query, a lumiera::QueryResolver instance is necessary, and this query resolver needs the ability to deal with this specific kind of query. Typically this is achieved by installing a resolution function into the resolver on application start. The QueryResolver returns a result set, actually a Query::Cursor, which can be used to enumerate multiple solutions, if any.

Queries are immutable, but it is possible to re-build and remould a query using a Query<TY>::Builder, accessible via Query::build() and Query::rebuild().

Note

as of 1/2013 this is rather a concept draft, but some parts of the code base are already actively using some more specific queries

See also

lumiera::QueryResolver

mobject::session::DefsManager

asset::StructFactory

config-resolver.hpp specialised setup for the Steam-Layer

fake-configrules.hpp currently used dummy-implementation

SessionServiceExploreScope

PlacementIndexQueryResolver

Definition in file query.hpp.

#include "lib/hash-combine.hpp"
#include "lib/typed-counter.hpp"
#include "lib/iter-adapter.hpp"
#include "lib/query-text.hpp"
#include "lib/query-util.hpp"
#include "lib/nocopy.hpp"
#include "lib/symbol.hpp"
#include "lib/util.hpp"
#include <boost/lexical_cast.hpp>
#include <boost/operators.hpp>
#include <memory>
#include <typeinfo>
#include <cctype>
#include <string>

Classes
class	Query< RES >::Builder
	Helper for establishing, reworking and remolding queries. More...
class	Query< RES >::Cursor
class	Goal
	Query ABC: unspecific goal for resolution or retrieval. More...
class	Query< RES >
	Generic interface to express a query for specifically typed result elements exposing some capabilities or fulfilling some properties. More...
struct	Goal::QueryID
class	QueryKey
	Wrapper for indexing and ordering. More...
class	Goal::Result
	Single Solution, possibly part of a result set. More...

Typedefs
typedef lib::TypedContext< Goal::Result >	ResultType
	Context used for generating type-IDs to denote the specific result types of issued queries.

Functions
template<typename RES >
IxID	getResultTypeID ()
bool	operator!= (Goal::QueryID const &id1, Goal::QueryID const &id2)
bool	operator< (Goal::QueryID const &id1, Goal::QueryID const &id2)
bool	operator== (Goal::QueryID const &id1, Goal::QueryID const &id2)
size_t	taggedHash (size_t hash, Goal::QueryID typeID)
	includes the QueryID type distinction into the given hash value

Namespaces
	lumiera
	Lumiera public interface.