Peewee

I'm excited about this release, as in addition to a number of new features and bugfixes, it also is a step towards cleaner code. I refactored the tests into a number of modules, using a standard set of base test-cases and helpers. I also introduced the `mock` library into the test suite and plan to use it for cleaner tests going forward. There's a lot of work to do to continue cleaning up the tests, but I'm feeling good about the changes. Curiously, the test suite runs faster now.

Bugs fixed

* 471, 482 and 484, all of which had to do with how joins were handled by the `aggregate_rows()` query result wrapper.
* 472 removed some needless special-casing in `Model.save()`.
* 466 fixed case-sensitive issues with the SQLite migrator.
* 474 fixed a handful of bugs that cropped up migrating foreign keys with SQLite.
* 475 fixed the behavior of the SQLite migrator regarding auto-generated indexes.
* 479 fixed a bug in the code that stripped extra parentheses in the SQL generator.
* Fixed a handful of bugs in the APSW extension.

New features

* Added connection abstraction called `ExecutionContext` ([see docs](http://docs.peewee-orm.com/en/latest/peewee/database.html#advanced-connection-management)).
* Made all context managers work as decorators (`atomic`, `transaction`, `savepoint`, `execution_context`).
* Added explicit methods for `IS NULL` and `IS NOT NULL` queries. The latter was actually necessary since the behavior is different from `NOT IS NULL (...)`.
* Allow disabling backref validation (465)
* Made quite a few improvements to the documentation, particularly sections on transactions.
* Added caching to the [DataSet](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#dataset) extension, which should improve performance.
* Made the SQLite migrator smarter with regards to preserving indexes when a table copy is necessary.

[View commits](https://github.com/coleifer/peewee/compare/2.4.4...2.4.5)

Biggest news: peewee has a new logo!


* Small documentation updates here and there.

Backwards-incompatible changes

* The argument signature for the `SqliteExtDatabase.aggregate()` decorator changed so that the aggregate name is the first parameter, and the number of parameters is the second parameter. If no values are specified, peewee will choose the name of the class and an un-specified number of arguments (`-1`).
* The logic for saving a model with a composite key changed slightly. Previously, if a model had a composite primary key and you called `save()`, only the dirty fields would be saved.

Bugs fixed

* 462
* 465, add hook for disabling backref validation.
* 466, fix case-sensitive table names with migration module.
* 469, save only dirty fields.

New features

* Lots of enhancements and cleanup to the `playhouse.apsw_ext` module.
* The `playhouse.reflection` module now supports introspecting indexes.
* Added a model option for disabling backref validation.
* Added support for the SQLite [closure table extension](http://charlesleifer.com/blog/querying-tree-structures-in-sqlite-using-python-and-the-transitive-closure-extension/).
* Added support for *virtual fields*, which act on dynamically-created virtual table fields.
* Added a new example: a virtual table implementation that exposes Redis as a relational database table.
* Added a module `playhouse.sqlite_aggregates` that contains a handful of aggregates you may find useful when developing with SQLite.


[View commits](https://github.com/coleifer/peewee/compare/2.4.3...2.4.4)

This release contains numerous improvements, particularly around the built-in database introspection utilities. Peewee should now also be compatible with PyPy.

Bugs fixed

* 466, table names are case sensitive in the SQLite migrations module.
* 465, added option to disable backref validation.
* 462, use the schema name consistently with postgres reflection.

New features

* New model *Meta* option to disable backref validation. [See validate_backrefs](http://docs.peewee-orm.com/en/latest/peewee/models.html#model-options-and-table-metadata).
* Added documentation on ordering by calculated values.
* Added basic PyPy compatibility.
* Added logic to close cursors after they have been exhausted.
* Structured and consolidated database metadata introspection, including improvements for introspecting indexes.
* Added support to [prefetch](http://docs.peewee-orm.com/en/latest/peewee/api.html?highlight=prefetch#prefetch) for traversing *up* the query tree.
* Added introspection option to skip invalid models while introspecting.
* Added option to limit the tables introspected.
* Added closed connection detection to the MySQL connection pool.
* Enhancements to passing options to creating virtual tables with SQLite.
* Added factory method for generating Closure tables for use with the `transitive_closure` SQLite extension.
* Added support for loading SQLite extensions.
* Numerous test-suite enhancements and new test-cases.

[View commits](https://github.com/coleifer/peewee/compare/2.4.2...2.4.3)

This release contains a number of improvements to the `reflection` and `migrate` extension modules. I also added an encrypted *diary* app to the [examples](https://github.com/coleifer/peewee/tree/master/examples) directory.

Bugs fixed

* 449, typo in the db_url extension, thanks to malea for the fix.
* 457 and 458, fixed documentation deficiences.

New features

* Added support for [importing data](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#importing-data) when using the [DataSet extension](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#dataset).
* Added an encrypted diary app to the examples.
* Better index reconstruction when altering columns on SQLite databases with the [migrate](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#migrate) module.
* Support for multi-column primary keys in the [reflection](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#reflection) module.
* Close cursors more aggressively when executing SELECT queries.

[View commits](https://github.com/coleifer/peewee/compare/2.4.1...2.4.2)

This release contains a few small bugfixes.

Bugs fixed

* 448, add hook to the connection pool for detecting closed connections.
* 229, fix join attribute detection.
* 447, fixed documentation typo.

[View commits](https://github.com/coleifer/peewee/compare/2.4.0...2.4.1)

This release contains a number of enhancements to the `playhouse` collection of extensions.

Backwards-incompatible changes

As of 2.4.0, most of the introspection logic was moved out of the ``pwiz`` module and into ``playhouse.reflection``.

New features

* Created a new [reflection](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#reflection) extension for introspecting databases. The *reflection* module additionally can generate actual peewee Model classes dynamically.
* Created a [dataset](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#dataset) library (based on the [SQLAlchemy project](https://dataset.readthedocs.io/) of the same name). For more info check out the blog post [announcing playhouse.dataset](http://charlesleifer.com/blog/saturday-morning-hacks-dataset-for-peewee/).
* Added a [db_url](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#database-url) module which creates `Database` objects from a connection string.
* Added [csv dump](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#dumping-csv) functionality to the [CSV utils](http://docs.peewee-orm.com/en/latest/peewee/playhouse.html#csv-utils) extension.
* Added an [atomic](http://docs.peewee-orm.com/en/latest/peewee/transactions.html#nesting-transactions) context manager to support nested transactions.
* Added support for HStore, JSON and TSVector to the `reflection` module.
* More documentation updates.

Bugs fixed

* Fixed 440, which fixes a bug where `Model.dirty_fields` did not return an empty set for some subclasses of `QueryResultWrapper`.

[View commits](https://github.com/coleifer/peewee/compare/2.3.3...2.4.0)