Wt

* \sa ptr::id(), loadLazy()

/*! \brief Lazy loads a persisted object.

*

* This method returns a database object with the given object id

* without directly accessing the database.

*

* If the object data is already available in the session, then it will

* be available upon return. Otherwise, the object data will be retrieved

* from the database on first access. Note: This will result in an

* ObjectNotFoundException if the object id is not valid.

*

* lazyLoad can be used to obtain a ptr<C> from a known id when a ptr<C>

* is required, but access to the C object is not anticipated. For

* instance, a ptr<C> may be required to add an object of class X that

* is in a belongsTo relationship with C.

*

* \sa ptr::id(), load()

*/

template <class C> ptr<C> loadLazy(const typename dbo_traits<C>::IdType& id);

/*

* Add posts with identical content to all user blogs, using various methods.

*/

BOOST_AUTO_TEST_CASE( dbo2_test2 )

{

Dbo2Fixture f;

dbo::Session& session = *f.session_;

typedef dbo::collection< dbo::ptr<User> > Users;

Post commonPost;

commonPost.contents = "Groupthink";

const size_t USER_COUNT = 2;

{

dbo::Transaction transaction(session);

for (int i = 0; i < USER_COUNT; i++) {

User *user = new User();

std::ostringstream os;

os << "User" << i;

user->name = os.str();

user->password = "Secret";

user->role = User::Visitor;

user->karma = i;

session.add(user);

}

}

{

dbo::Transaction transaction(session);

commonPost.title = "Post 1";

std::cerr << "\nAdding '" << commonPost.title << "' to " << USER_COUNT

<< " user blogs iterating over user objects" << std::endl;

/*

* Complete user objects are retrieved from DB, although only the id is

* needed. This could be costly with a more complex User record.

*/

Users allUsers = session.find<User > ();

for (Users::const_iterator i = allUsers.begin();

i != allUsers.end(); ++i) {

dbo::ptr<User> user = *i;

commonPost.user = user;

dbo::ptr<Post> post = session.add(new Post(commonPost));

}

}

{

dbo::Transaction transaction(session);

commonPost.title = "Post 2";

std::cerr << "\nAdding '" << commonPost.title << "' to " << USER_COUNT

<< " user blogs using dbo::ptr link from existing posts" << std::endl;

/*

* If there is an existing dbo::ptr to a user, we can add new Posts

* without retrieving the associated user by copying the dbo::ptr.

* NOTE: This works because we have a single post, "Post 1", for each user.

*/

Posts existingPosts = session.find<Post > ();

for (Posts::const_iterator i = existingPosts.begin();

i != existingPosts.end(); ++i) {

commonPost.user = (*i)->user;

dbo::ptr<Post> post = session.add(new Post(commonPost));

}

}

{

dbo::Transaction transaction(session);

commonPost.title = "Post 3";

std::cerr << "\nAdding '" << commonPost.title << "' to " << USER_COUNT

<< " user blogs using insert through user objects" << std::endl;

/*

* With insert(), the full User object is retrieved for each post,

* even though only the id is required. The User object is also

* updated (incremented version number).

*/

Users allUsers = session.find<User > ();

for (Users::const_iterator i = allUsers.begin();

i != allUsers.end(); ++i) {

i->modify()->posts.insert(new Post(commonPost));

}

}

{

dbo::Transaction transaction(session);

commonPost.title = "Post 4";

std::cerr << "\nAdding '" << commonPost.title << "' to " << USER_COUNT

<< " user blogs using load to retrieve user objects" << std::endl;

typedef dbo::dbo_traits<User>::IdType UserId;

typedef dbo::collection< UserId > UserIds;

/*

* With load(), the full User object is retrieved for each post,

* even though only the id is required.

*/

UserIds allUserIds = session.query<UserId > ("select u.\"id\" from \"user\" u");

for (UserIds::const_iterator i = allUserIds.begin();

i != allUserIds.end(); ++i) {

commonPost.user = session.load<User>(*i);

dbo::ptr<Post> post = session.add(new Post(commonPost));

}

}

{

dbo::Transaction transaction(session);

commonPost.title = "Post 5";

std::cerr << "\nAdding '" << commonPost.title << "' to " << USER_COUNT

<< " user blogs using loadLazy to retrieve user objects" << std::endl;

typedef dbo::dbo_traits<User>::IdType UserId;

typedef dbo::collection< UserId > UserIds;

/*

* With loadLazy(), there is no need to retrieve the full User object

* in order to obtain a dbo::ptr to the User for adding posts.

*/

UserIds allUserIds = session.query<UserId > ("select u.\"id\" from \"user\" u");

for (UserIds::const_iterator i = allUserIds.begin();

i != allUserIds.end(); ++i) {

commonPost.user = session.loadLazy<User>(*i);

dbo::ptr<Post> post = session.add(new Post(commonPost));

}

}

{

dbo::Transaction transaction(session);

std::cerr << std::endl;

/*

* Each user should now have 5 posts

*/

Users allUsers = session.find<User > ();

for (Users::const_iterator i = allUsers.begin();

i != allUsers.end(); ++i) {

dbo::ptr<User> user = *i;

BOOST_REQUIRE(user->posts.size() == 5);

}

}

}