SQLite Data Change Notification Callbacks in Pytho

问题:

SQLite has Data Change Notification Callbacks available in the C API. Can these callbacks be used from the SQLite CLI, or from Bash or from Python?

If so, how?

回答1:

Can these callbacks be used from the SQLite CLI...

Reading through the SQLite source code, it doesn't look like that function is used anywhere in the CLI source code, so I doubt you can do it via the CLI.

...or from Bash...

Not sure what you mean by that.

...or from Python?

It's not exposed via the standard sqlite3 module, but you can use it with the ctypes module.

If so, how?

Here's a quick n' dirty example of using it via ctypes...

from ctypes import *

# Define some symbols
SQLITE_DELETE =  9
SQLITE_INSERT = 18
SQLITE_UPDATE = 23

# Define our callback function
#
# 'user_data' will be the third param passed to sqlite3_update_hook
# 'operation' will be one of: SQLITE_DELETE, SQLITE_INSERT, or SQLITE_UPDATE
# 'db name' will be the name of the affected database
# 'table_name' will be the name of the affected table
# 'row_id' will be the ID of the affected row
def callback(user_data, operation, db_name, table_name, row_id):
    if operation == SQLITE_DELETE:
        optext = 'Deleted row'
    elif operation == SQLITE_INSERT:
        optext = 'Inserted row'
    elif operation == SQLITE_UPDATE:
        optext = 'Updated row'
    else:
        optext = 'Unknown operation on row'
    s = '%s %ld of table "%s" in database "%s"' % (optext, row_id, table_name, db_name)
    print s

# Translate into a ctypes callback
c_callback = CFUNCTYPE(c_void_p, c_void_p, c_int, c_char_p, c_char_p, c_int64)(callback)

# Load sqlite3
dll = CDLL('libsqlite3.so')

# Holds a pointer to the database connection
db = c_void_p()

# Open a connection to 'test.db'
dll.sqlite3_open('test.db', byref(db))

# Register callback
dll.sqlite3_update_hook(db, c_callback, None)

# Create a variable to hold error messages
err = c_char_p()

# Now execute some SQL
dll.sqlite3_exec(db, 'create table foo (id int, name varchar(255))', None, None, byref(err))
if err:
    print err.value
dll.sqlite3_exec(db, 'insert into foo values (1, "Bob")', None, None, byref(err))
if err:
    print err.value

...which prints out...

Inserted row 1 of table "foo" in database "main"

...on the first run and...

table foo already exists
Inserted row 2 of table "foo" in database "main"

...on the second run.