Where it was required only to pass down to the CT_TIMESPEC specialization
of template<GncSqlObjectType Type>GncSqlColumnTableEntryImpl::add_to_query().
Since these are now parent-class member functions they can be called
directly from dbi_be without any casting gymnastics.
Also: Move the GncSqlObjectBackend registry to its own class, a private
member of GncSqlBackend. This eliminates a static variable in gnc-backend-sql.cpp
and allows the GncSqlBackend::ObjectRegistry constructor to insert all of
the backends into the list, eliminating gnc_sql_init() and all of the
gnc_sql_init_foo_handler() functions. The cost of this is that the objects
are now created on the free store instead of the text segment.
Because the object backends are created at GncSqlBackend construction
there is now a GncSqlBookBackend in the registry and the second error
message in test_gnc_sql_commit_edit is no longer emitted; instead, the
object is properly committed.
Unfortunately a rather massive change. Gets rid of GncSqlColumnTypeHandler
and its hideous run-time registry by making the handler functions members
of GncSqlColumnTableEntry. GncSqlColumnTableEntry becomes an abstract super-
class with a templatized subclass GncSqlColumnTableEntryImpl whose template
parameter is the GncSqlObjectType that's also the GncSqlColumnTableEntryImpl's
m_col_type member. That member is a candidate for future removal as it's not
necessary. An explicit specialization is provided for each GncSqlObjectType and
that's a candidate for future code-shrinkage as there's still a fair amount
of duplication in spite of adding several helper template functions to absorb
most of the meat. The abstract GncSqlColumnTableEntry class is motivated by
the need to have an iterable container which in turn requires runtime
polymorphism. This can probably be replaced with a variadic-template
pseudo-container.
The two major benefits of this change are that it gets rid of one more set
of macro functions and provides vtable dispatch that has only one level
of indirection instead of the cumbersome string-hash-table-lookup to
find the handler followed by invoking the handler's function.
The two header files are removed because they exposed only the initialization
function which in turn only registered the respective GncSqlColumnTypeHandler.
The two lists were always used together so replace them with a single
vector of std::pair<std::string, std::string>; this also gets rid of the
intermediate GValue which was used to convert the returned value to a string.
operator<<() can do that for us more transparently.
Also template most of the add_value_to_vec functions.
