Suppose you cache counts of tweets for every user in a special table to avoid an expensive COUNT() query. You want to update the cache table every time a user tweets, but do so atomically: cache_row = CacheCount CacheCount.get(user=some_user) update_query = cache_row.update(tweet_count=F('tweet_count') + 1) update_query.execute() Aggregating records Suppose you have some blogs and want to get a list of them along @connect(post_save, sender=MyModel) def on_save_handler(model_class, instance, created): put_data_in_cache(instance.data) The following signals are provided: pre_save Called immediately before an object

Suppose you cache counts of tweets for every user in a special table to avoid an expensive COUNT() query. You want to update the cache table every time a user tweets, but do so atomically: cache_row = CacheCount CacheCount.get(user=some_user) update_query = cache_row.update(tweet_count=F(’tweet_count’) + 1) update_query.execute() Aggregating records Suppose you have some blogs and want to get a list of them along @connect(post_save, sender=MyModel) def on_save_handler(model_class, instance, created): put_data_in_cache(instance.data) The following signals are provided: pre_save Called immediately before an object

# SQLite database using WAL journal mode and 64MB cache. sqlite_db = SqliteDatabase('/path/to/app.db', pragmas={ 'journal_mode': 'wal', 'cache_size': -1024 * 64}) # Connect to a MySQL database SqliteExtDatabase('my_app.db', pragmas={ 'journal_mode': 'wal', # WAL-mode. 'cache_size': -64 * 1000, # 64MB cache. 'synchronous': 0}) # Let the OS manage syncing. PRAGMA statements SQLite allows pragma name and value: db = SqliteDatabase('my_app.db', pragmas={ 'journal_mode': 'wal', 'cache_size': 10000, # 10000 pages, or ~40MB 'foreign_keys': 1, # Enforce foreign-key constraints })

specific configuration options. from peewee import * # SQLite database using WAL journal mode and 64MB cache. sqlite_db = SqliteDatabase('/path/to/app.db', pragmas={ (continues on next page) 18 Chapter 1. Contents: peewee Documentation, Release 3.6.0 (continued from previous page) 'journal_mode': 'wal', 'cache_size': -1024 * 64}) # Connect to a MySQL database on network. mysql_db = MySQLDatabase('my_app', = SqliteExtDatabase('my_app.db', pragmas={ 'journal_mode': 'wal', # WAL-mode. 'cache_size': -64 * 1000, # 64MB cache. 'synchronous': 0}) # Let the OS manage syncing. PRAGMA statements SQLite allows

# SQLite database using WAL journal mode and 64MB cache. sqlite_db = SqliteDatabase('/path/to/app.db', pragmas={ 'journal_mode': 'wal', 'cache_size': -1024 * 64}) # Connect to a MySQL database SqliteExtDatabase('my_app.db', pragmas={ 'journal_mode': 'wal', # WAL-mode. 'cache_size': -64 * 1000, # 64MB cache. 'synchronous': 0}) # Let the OS manage syncing. PRAGMA statements SQLite allows pragma name and value: db = SqliteDatabase('my_app.db', pragmas={ 'journal_mode': 'wal', 'cache_size': 10000, # 10000 pages, or ~40MB 'foreign_keys': 1, # Enforce foreign-key constraints })

* # SQLite database using WAL journal mode and 64MB cache. sqlite_db = SqliteDatabase('/path/to/app.db', pragmas={ 'journal_mode': 'wal', 'cache_size': -1024 * 64}) # Connect to a MySQL database on = SqliteExtDatabase('my_app.db', pragmas={ 'journal_mode': 'wal', # WAL-mode. 'cache_size': -64 * 1000, # 64MB cache. 'synchronous': 0}) # Let the OS manage syncing. PRAGMA statements SQLite allows containing the pragma name and value: db = SqliteDatabase('my_app.db', pragmas={ 'journal_mode': 'wal', 'cache_size': 10000, # 10000 pages, or ~40MB 'foreign_keys': 1, # Enforce foreign-key constraints }) PRAGMAs

# SQLite database using WAL journal mode and 64MB cache. sqlite_db = SqliteDatabase('/path/to/app.db', pragmas=( ('journal_mode', 'wal'), ('cache_size', -1024 * 64))) # Connect to a MySQL database pragma name and value: db = SqliteDatabase('my_app.db', pragmas=( ('journal_mode', 'WAL'), ('cache_size', 10000), ('mmap_size', 1024 * 1024 * 32), )) PRAGMAs may also be configured dynamically Set cache size to 64MB for current connection. db.pragma('cache_size', -1024 * 64) # Same as above. db.cache_size = -1024 * 64 # Read the value of several pragmas: print('cache_size:', db.cache_size)

@connect(post_save, sender=MyModel) def on_save_handler(model_class, instance, created): put_data_in_cache(instance.data) The following signals are provided: pre_save Called immediately before an object from playhouse.signals import post_save from project.handlers import cache_buster post_save.connect(cache_buster, name=’project.cache_buster’) disconnect([receiver=None[, name=None]]) Disconnect the given – the callback to disconnect • name (string) – a short alias post_save.disconnect(name=’project.cache_buster’) 1.10. Playhouse, a collection of addons 59 peewee Documentation, Release 2.0.0 send(instance

# SQLite database using WAL journal mode and 64MB cache. sqlite_db = SqliteDatabase('/path/to/app.db', pragmas=( ('journal_mode', 'wal'), ('cache_size', -1024 * 64))) # Connect to a MySQL database pragma name and value: db = SqliteDatabase('my_app.db', pragmas=( ('journal_mode', 'WAL'), ('cache_size', 10000), ('mmap_size', 1024 * 1024 * 32), )) PRAGMAs may also be configured dynamically Set cache size to 64MB for current connection. db.pragma('cache_size', -1024 * 64) # Same as above. db.cache_size = -1024 * 64 # Read the value of several pragmas: print('cache_size:', db.cache_size)

# SQLite database using WAL journal mode and 64MB cache. sqlite_db = SqliteDatabase('/path/to/app.db', pragmas=( ('journal_mode', 'wal'), ('cache_size', -1024 * 64))) # Connect to a MySQL database pragma name and value: db = SqliteDatabase('my_app.db', pragmas=( ('journal_mode', 'WAL'), ('cache_size', 10000), ('mmap_size', 1024 * 1024 * 32), )) PRAGMAs may also be configured dynamically Set cache size to 64MB for current connection. db.pragma('cache_size', -1024 * 64) # Same as above. db.cache_size = -1024 * 64 # Read the value of several pragmas: print('cache_size:', db.cache_size)