[odb-users] ODB 1.6.0.a2 available
boris at codesynthesis.com
Thu Sep 22 08:02:35 EDT 2011
The second alpha version for the upcoming ODB 1.6.0 is now available.
The major new feature in this release compared to the earlier 1.6.0.a1
is support for views.
View is a light-weight, read-only projection of one or more persistent
objects, ad-hoc database tables, or some combination of the two. For
#pragma db view object(employee) object(employer)
#pragma db column(employer::name)
typedef odb::query<employee_info> query;
typedef odb::result<employee_info> result;
result r = db.query<employee_info> (
query::employee::last_name == "Doe" &&
query::employer::name == "Simple Tech, Inc");
We are still working on the documentation and examples for this feature,
but seeing that a lot of people asked for it, we have decided to make a
pre-release as soon as possible. In the meantime the test.hxx file in
the common/view test in the odb-tests package gives a good overview of
Other NEWS file entries so far are:
* New function, database::erase_query(), allows the deletion of the
database state of multiple objects matching certain criteria. It uses
the same query expression as the database::query() function. For more
information, refer to Section 3.10, "Deleting Persistent Objects" in
the ODB manual.
* Support for value wrappers. An ODB value wrapper is a class template
that wraps a value type or a container. Common examples of wrappers
are smart pointers, holders, and "optional value" containers such as
boost::optional. A wrapper can be transparent or it can handle the
NULL semantics. To allow the easy conversion of value types that do
not support the NULL semantics into the ones that do, the odb::nullable
class template has been added. ODB also now includes built-in support for
std::auto_ptr and std::tr1::shared_ptr smart pointers as value wrappers
as well as for boost::shared_ptr and QSharedPointer via the Boost and Qt
profiles. Currently, the NULL semantics is only supported for simple
values but smart pointers can still be used with composite values and
containers. For more information, refer to Section 7.3, "NULL Value
Semantics" in the ODB manual.
* Support for the boost::optional container in the Boost profile. A data
member of the boost::optional type is mapped to a column that can have
a NULL value. For more information, refer to Section 15.3 "Optional
Library" in the ODB manual.
* Support for mapping std::vector<char> to the BLOB (or equivalent) types.
For more information, refer to chapters 11 (for MySQL), 12 (for SQLite)
and 13 (for PostgreSQL) in the ODB manual.
* New option, --table-prefix, allows the specification of a prefix that
is added to table and index names. For more information, refer to the
ODB compiler command line interface documentation (man pages).
* New ODB runtime interface, odb::connection, represents a connection
to the database. The primary use case for a connection is to execute
native statements outside of a transaction. For more information, refer
to Section 3.5, "Connections" in the ODB manual.
* Support for multiplexing several transaction on the same thread. For
more information, refer to Section 3.4, "Transactions" in the ODB
* All the concrete connection classes now have a second constructor which
allows the creation of a connection instance from an already established
underlying connection handle. The connection_pool_factory and, in case of
SQLite, single_connection_factory now have a virtual create() function
that can be overridden to implement custom connection establishment and
* The query expression syntax for object pointers and composite values has
changed. Now, instead of using the scope resolution operator ('::') the
member access via pointer operator (->) is used for object pointers and
the member access operator (.) is used for composite values. Examples of
old and new syntax for pointers, old: query<employee>::employer::name
and new: query<employee>::employer->name. For composites values, old:
query<employee>::name::first and new: query<employee>::name.first.
* SQLite ODB runtime now enables foreign key constraints checking by
default. While this should not affect correct applications, due to
bugs in SQLite DDL foreign keys support, you may need to temporarily
disable foreign key constraints checking when re-creating the database
schema (the sign that you may need to do so is the "foreign key
constraint failed" exception thrown by the commit() function after the
call to schema_catalog::create_schema()). For more information, refer
to Section 12.5.3, "Foreign Key Constraints" in the ODB manual.
* Support for specifying the client character set for the MySQL database.
For more information, refer to Section 11.2, "MySQL Database Class" in
the ODB manual.
* Object cache maintained by a session nor longer distinguishes between
const and non-const objects. Instead, const objects are treated as
non-const by casting away constness. For more information on this new
behavior, refer to Section 9.1, "Object Cache" in the ODB manual.
This pre-release (as well as all the future pre-releases) is available
The ODB compiler binaries are only available for Windows and GNU/Linux
(x86 and x86_64).
Testing and feedback are appreciated.
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