使用SQLite作为键:值存储
使用SQLite作为键:值存储
提问于 2017-11-11 20:20:17
正如Key: value store in Python for possibly 100 GB of data, without client/server的评论和其他问题所建议的那样，SQLite完全可以用作持久化的键:值存储。
如何定义一个类(或者仅仅是包装器函数)，以便在SQLite中使用key:value存储就像下面这样简单：
kv = Keyvaluestore('/test.db')
kv['hello'] = 'hi' # set
print(kv['hello']) # get
print('blah' in kv) # answer: False because there's no key 'blah' in the store
kv.close()回答 3
Stack Overflow用户
回答已采纳
发布于 2017-11-12 01:37:55
即使存在这样做的模块(参见其他答案)，我也试图编写一个简单的、自包含的版本。下面是一个类KeyValueStore (键和值都是字符串)，它的工作方式如下：
演示
from sqlitekeyvaluestore import KeyValueStore
kv = KeyValueStore('test.db') # uses SQLite
print(len(kv)) # 0 item
kv['hello1'] = 'you1'
kv['hello2'] = 'you2'
kv['hello3'] = 'you3'
print(kv['hello1']) # you1
print(len(kv)) # 3 items
del kv['hello1']
print(len(kv)) # 2 items remaining
print('hello1' in kv) # False, it has just been deleted!
print('hello3' in kv) # True
kv['hello3'] = 'newvalue' # redefine an already present key/value
print(kv['hello3']) # newvalue
print(kv.keys()) # ['hello2', 'hello3']
print(kv.values()) # ['you2', 'newvalue']
print(kv.items()) # [('hello2', 'you2'), ('hello3', 'newvalue')]
for k in kv:
print(k, kv[k])
kv.close() # important to commit代码: sqlitekeyvaluestore.py
import sqlite3
class KeyValueStore(dict):
def __init__(self, filename=None):
self.conn = sqlite3.connect(filename)
self.conn.execute("CREATE TABLE IF NOT EXISTS kv (key text unique, value text)")
def close(self):
self.conn.commit()
self.conn.close()
def __len__(self):
rows = self.conn.execute('SELECT COUNT(*) FROM kv').fetchone()[0]
return rows if rows is not None else 0
def iterkeys(self):
c = self.conn.cursor()
for row in self.conn.execute('SELECT key FROM kv'):
yield row[0]
def itervalues(self):
c = self.conn.cursor()
for row in c.execute('SELECT value FROM kv'):
yield row[0]
def iteritems(self):
c = self.conn.cursor()
for row in c.execute('SELECT key, value FROM kv'):
yield row[0], row[1]
def keys(self):
return list(self.iterkeys())
def values(self):
return list(self.itervalues())
def items(self):
return list(self.iteritems())
def __contains__(self, key):
return self.conn.execute('SELECT 1 FROM kv WHERE key = ?', (key,)).fetchone() is not None
def __getitem__(self, key):
item = self.conn.execute('SELECT value FROM kv WHERE key = ?', (key,)).fetchone()
if item is None:
raise KeyError(key)
return item[0]
def __setitem__(self, key, value):
self.conn.execute('REPLACE INTO kv (key, value) VALUES (?,?)', (key, value))
def __delitem__(self, key):
if key not in self:
raise KeyError(key)
self.conn.execute('DELETE FROM kv WHERE key = ?', (key,))
def __iter__(self):
return self.iterkeys()Stack Overflow用户
发布于 2017-11-11 20:42:06
已经有了sqlitedict，它似乎可以满足您的所有需求。
从文档中：
from sqlitedict import SqliteDict
mydict = SqliteDict('./my_db.sqlite', autocommit=True)
mydict['some_key'] = any_picklable_object
print(mydict['some_key']) # prints the new value
for key, value in mydict.iteritems():
print(key, value)
print(len(mydict)) # etc... all dict functions work
mydict.close()Stack Overflow用户
发布于 2021-03-01 16:05:33
我喜欢Basj的回答，但我还想在KeyValueStore类中添加以下函数，以便在使用DB时，我们可以在不关闭数据库的情况下提交数据。
class KeyValueStore(dict):
"""Other functions"""
def commit(self):
self.conn.commit()页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/47237807
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