[PonyORM-list] Pony ORM Release 0.5-beta

[Alexey Malashkevich]

Pony ORM 0.5-beta is released!

New transaction model
---------------------

Before this release Pony supported two separate transaction
modes: standard and optimistic. In this release we've combines
both of them into one. Now user can choose which locking
mechanism should be use for any specific object. By default
Pony uses the optimistic locking. This means, that the database
doesn't lock any objects in the database. In order to be sure
that those objects weren't updated by a concurrent transaction,
Pony checks the corresponding database rows during update.

Sometimes a user might want to go with the pessimistic locking.
With this approach the database locks the corresponding rows
for the exclusive access in order to prevent concurrent modification.
It can be done with the help of "for update" methods. In this
case there is no need for Pony to do the optimistic check.
You can use any of the following methods:

    prod_list = select(p for p
                         in Product if p.price > 100).for_update()
    prod_list = Product.select(lambda p: p.price > 100).for_update()
    p = Product.get_for_update(id=123)

Pony ORM transaction processing is described in more detail in
the newly created documentation chapter Transactions.


Documentation
-------------

In this release we have added the ability to add comments to our
online documentation, please leave your feedback, questions, comments.
We need you in order to make Pony ORM documentation better.


Filtering the query results
---------------------------

With this release we introduce a new method of the "Query" object:
"filter()". It can be convenient for applying conditions for an
existing query. You can find more information in the documentation


Database late binding
---------------------

Pony ORM users were asking us to provide a way to bind the database
at a later stage. This is convenient for testing. The goal of
Pony ORM team is to provide a convenient tool for working with
databases and in this release we've added such a possibility.

Before this release the process of mapping entities to the database
was as following:

    db = Database('sqlite', 'database.sqlite')

    class Entity1(db.Entity):
        ...

    # other entities declaration

    db.generate_mapping(create_tables=True)

Now besides the approach described above, you can use the following way:

    db = Database()

    class Entity1(db.Entity):
        ...

    # other entities declaration

    db.bind('sqlite', 'database.sqlite')
    db.generate_mapping(create_tables=True)


Other features and bugfixes
---------------------------

- Added method Query.page() for pagination
- Added count() method for collections. E.g. Customer[123].orders.count()
- Added ORDER BY RANDOM(): MyEntity.select_random(N),
  MyEntity.select(...).random(N), select(...).random(N) - where N is the number
  of elements to be selected
- Bugfix in exists() subquery
- Bugfix when the same item was added and removed within the same
transaction
- Aggregations bugfix
- The support of PyGreSQL is discontinued. Using psycopg2 instead
- Added pony.__version__ attribute
- Stability and performance improvements

Regards,
Alexey Malashkevich
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